A factor more influential toward successful high-performance engine building than any other is the cylinder heads. Without adequate airflow, the engine will never make power. The areas one inch before to about a half inch after the intake valve, and similarly for the exhaust, are the most difficult flow restrictions to minimize in the entire engine. In addition to flow, aspects such as swirl, port velocity, and combustion characteristics also play major parts. This means that the cylinder heads you elect to use and what you subsequently do to them is the prime factor dictating the power achieved.
Since the introduction of the small-block Chevy in 1955 up to the late 1990s, a small budget meant a limited choice of heads for performance. Until the turn of the millennia a restricted budget meant buying cylinder heads from a wrecking yard, a private third party source, a swap meet, or a reputable discount performance auto supplier. If a little luck swung our way we just might pick some functional aftermarket aluminum heads at a rock-bottom price on eBay. But luck is an element that can’t be counted on.
This Tech Tip is From the Full Book “HOW TO BUILD MAX-PERFORMANCE CHEVY SMALL BLOCK ENGINES“. For a comprehensive guide on this entire subject you can visit this link:
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Fortunately, from about 2000 on, the amount we had to rely on luck started to decline considerably as far as heads were concerned. About that time, the aftermarket demand for low-cost performance orientated heads had grown to such an extent that affordable options expanded beyond almost everybody’s expectations. When I wrote the first edition of this book, the budget meant we were almost certainly locked into using production heads. That is no longer the case. We have moved on, and I will deal only minimally with factory-produced heads. While on the subject, I will tell you what to avoid and what to use if your build involved factory heads. As far as aftermarket heads are concerned, there are several brands of iron heads that work well out of the box and port up very easily to deliver very professional results even when done by a novice. Also, volume production has meant that not only are aluminum heads a financial practicality, even when a relatively restricted budget is involved, but also at least, one brand of CNC head falls into an affordable budget for most engine builders. Sure it’s at the top end of the sort of budgets we are dealing with here, but nonetheless it is a good indicator of the expansion of the market that has taken place.
Let’s deal with the options for those on the very smallest of budgets. Other than buying a set of used aftermarket heads that, of course, will us to factory heads.
Factory Heads For Performance
Although I have not tested every single small-block Chevy casting, I have pretty much tested every sub group. If your budget constrains you to use a factory casting, then be aware you can make or break your engine’s final output right here. Here what is needed in the way of heads for the best return on investment:
- Good combustion characteristics.
- Good flow potential.
- A small enough chamber volume to get a working compression ratio without an excessively high, plug-masking, piston crown.
When making a choice of production heads, always consider these three points. If you lose sight of them, your project will suffer. For the really-low-budget build, let’s consider early iron heads—those cast before about 1980. Aside from cracking problems there are, for power production, two distinct groups of production heads. There are those that should be avoided like the plague because they don’t make torque or horsepower, and there are those that do. Fortunately, it’s easy to determine which group an unlisted cylinder head you may be looking at falls into. The combustion chamber style is usually the giveaway. Take a look at the combustion chamber photo on this page. This is the closed-style chamber as opposed to the “open” or smog-style chamber. The open chamber, used predominantly for low-compression car, truck, and smog applications fromthe mid-60s into the late 70s must be avoided. Using these open-chamber heads can cost up to 30 ft-lbs and a like amount of HP on a relatively mild street build. Avoid such castings even if they have the bigger 2.02/1.6 valves in them.
If the budget means early-style heads (as opposed to the later Vortec heads) then closed chamber heads are definitely the ones to look for. The only drawback to these heads is that they suffer from a little more valve shrouding (see Fig 6-1) than is necessary, and sometimes chamber cracking (details on cracking later in his chapter).
Once these heads have been overhauled porting is relatively straightforward in the initial stages and produces good results. However, getting ultimate results requires practice and a flow bench. Even in simple pocket-ported form and used in conjunction with other appropriate parts, they can produce excellent results. The way to do both pocket and the more advanced porting is detailed later.
In addition to early heads, the 1986 and later Tuned Port Injected (TPI) 350 H.O. motors, such as the Pontiac Trans Am and Chevy Camaro, are worth having. These heads have chambers that look like they’ve inherited some smog-head characteristics, but they’re sufficiently removed to fall well short of that category. They have relatively small combustion chambers, and the basic engine sports compression ratios of 9:1 or more. These heads will port out well, but be aware that 305 heads have smaller valves, so only look for 350 heads unless you’re specifically working on a 305. This will save you the expense of extra machining to put in larger valves.
Also, if the porting technician is too exuberant, there’s the possibility of porting these into the water jacket. The last two head styles on the list may be a little expensive, but they’re increasingly becoming available on the used market. The first of these is the aluminum L98 Corvette head casting, produced between about 1986 and 1993. In stock form these heads are nothing special—just light.
Although they won’t accept valves larger than 2.00 on the intake side and 1.55 on the exhaust without fitting larger inserts, they nonetheless can, in ported form as detailed later, produce some truly impressive results for a high-output street motor. On a 383 motor equipped with a single four-barrel carb, not only can the aluminum Corvette heads be made to produce in excess of 450 hp, but also deliver excellent low-end output for true street drivability.
The L31 heads from the late-model 350 Vortec engine, introduced early in 1995, is the other type of cylinder head you need to look for on the used market. This is probably the best cylinder head casting that Chevrolet has ever produced for a production small block Chevy. The casting quality is as good as the best aftermarket iron heads, and its flow capability on a valve-size-for-size basis more than matches the Phase 6 aluminum Bowtie heads.
With the installation of larger valves, it will not only generate sufficient flow for good top-end horsepower, but the Vortec’s high swirl and port velocity also means exceptionally good low-end output. With just bigger valves and a simple pocket porting job, those with relatively little porting experience achieved favorable results (shown later). Therefore, you should put late-model Vortec heads high on your used, factory- head priority list.
Production Head Overhaul
Other than Vortec heads, most of the “desirable” castings you will locate could be as much as 30 years old, or older, and will need a rebuild. As stated earlier, you should have bought them with some kind of assurance that if they’re cracked you can get your money back.
You will need to check the following and figure whatever it costs to do could have been money spent toward new aftermarket heads.
- Crack test
- Oven bake/ball peen clean
- Check guide wear; new guides/guide job are almost a certainty here
- Machine for screw-in studs if springs heavier than stock are to be used
- Machine stud bosses for pushrod guide plates
- Valve seat machining
- Spring pocket machining for larger diameter springs
- Mill head face
Now your heads may not need all these ops done (although they most likely will), but even so, you are going to come out of this with a sizable machine shop bill. This means you should factor this in the cash equation. It may well be worth the effort to round up that extra money for a set of new aftermarket heads with all the features we are trying to achieve here, ready to go.
Let’s talk a little more about guides before moving on. Ideally, the valve-stem-to-guide clearances need to be about 0.0015 inch on the intake and 0.002 inch for the exhaust clearance. With older used heads, this is unlikely to be the case, so let’s look at the maximum limits. Anything more than 0.004 inch on the exhaust and 0.0035 inch on the intake will start to reduce power because the valves will not seat properly. Also, loose guides will cause whatever valve job may be done on the heads to wear faster because the valve lands on the seat in a different position each time.
Worn guided can be fixed with oversize stem valves or the installation of new press-in guides.
Valve Sizes and Seat Recession
Decisions on valve sizes need to be made at this point. Anything less than 1.94/1.5 intake/exhaust combination in a bore of 4 inches or more isn’t going to produce the most desirable results. The most common highperformance valve size combination is 2.02 inch for the intake and 1.6 for the exhaust.
If your existing valves have good stems, the use of 1.94 intakes doesn’t give away significantly to 2.02s. If wear dictates going to the 2.02s, then have the seats and chamber cut accordingly. The installation of the bigger valves can cost as much as $50 over that of a regular valve job. However, be aware that if you decide to stick to the 1.94/1.5 valve combination, you still can get decent results at a lower cost.
As far as a valve seat job is concerned the usual situation is that the valves, especially the exhaust, have become recessed into the head. Although machine shops offer a shallow- angle valve seat top-cut service that removes the effect of small or moderate amounts of recession, it still can leave the valve too low in the head. If the cylinder head looks as if it needs work to cure recession, consider having larger valves installed because that has the potential for more flow as well as fixing the recession problem.
Another factor to consider is that earlier production heads don’t have armored seats for use with unleaded fuel. Don’t worry about this, unless your intent is to build a high-mileage street driver. If you must have armored seats, you should consider using an aftermarket head because these heads have them out of the box.
Most beginners wrongly presume that port shape and roughness are the flow-limiting factors. All too often it’s assumed that the valve seats play only a minor role as far as flow is concerned. It’s certainly appreciated that the seat plays its part at low lift, but the significance doesn’t stop at low lift, as we shall see later. Take a look at Fig 6-3 and Fig 6-4 for some working dimensions.
Correcting Excessive Guide Clearance
If seats need reconditioning, consider the method of acquiring the desired valve-stem-to-guide clearance. It is most cost effective to use valves that have oversized stems. PEP and Engine Tech (and others) supply such valves with oversized stems (available at many engine re-con shops). Engine Tech also supplies valves that not only have oversized stems, but also heads typically 0.025- to 0.030-inch oversized. This is an ideal, low-cost way to fix recession in heads that already have the 2.02/1.6 combination, as do some production line, high-performance vehicles.
Cast-iron guides, though functional in terms of wear, aren’t necessarily the best. I recommend two options: the thin-wall bronze guides, such as those produced by K-Line or PEP, or the thick-wall bronze guides commonly available from most engine re-con shops. All are effective in terms of low wear rates.
If you’re putting together a costconscious head package and you want the best bang for the buck, be aware you are going to need to do some checking around. Many machine shops are not eager to take on performance-orientated work. Now that may sound like bad news but on the flip side of the coin,the high-performance market is expanding while the plain engine reconditioning business is shrinking. The shops that are surviving this contraction are those willing to do work at a reasonable cost for folks like us who want to go as fast as our slim budgets will allow. To get the most from a basic 3-angle valve job, the best plan is to photocopy our seat drawings and ask what it will cost to get your seats done like that. It will vary from head to head as the amount of metal to come out will be different depending on what size of valves where there to start with.
Along with a valve seat job, some basic valve reshaping will be required to make it all work well together. Almost all the valves available offthe- shelf need some work done to improve airflow.
The simplest and most effective mod is to “back cut” both the intake and exhaust valves as per Fig 6-5. The final valve seat width needs to be just a little more than that used in the head. On the exhaust valve, it’s important that the front face-tomargin has a generous radius. This radius considerably enhances low-lift flow and cuts the temperature of the exhaust valve.
Accommodating High-Performance Springs
The next few moves with production- line heads depend on cam choice (see Chapter 7) and the springs it requires. If the valve spring loads are not going to exceed 220 pounds at full lift, you can, for the most part, get away with the stock press-in studs. If the intended spring, cam, and spring combination to be used have sufficient lift to warrant a spring of significantly more than 220 pounds over the nose, then screw-in studs are needed. If these are a requirement, you will almost certainly need to convert to guide plates for the pushrod instead of the plain slot in the casting. This I easily done at the time of stud installation.
The more aggressive cams will require the spring pocket machined to accept a larger-diameter spring. This operation costs money even if you buy the special tool from the cam company and, with an electric drill, do it yourself. So when you’re selecting a camshaft, you need to consider what spring it should be used with and whether this spring requires the heads to be machined and whether or not the head can be machined sufficiently for the spring intended.
Basic Small-Block Chevy Head Porting
The following information on porting deals with 23-degree Chevy heads pretty much across the board. Applying what is detailed in the next dozen pages on heads will allow you to generate more airflow and, consequently, more power.
But just a moment, you’re a beginner and you don’t have a flow bench. If you fall into that category, listen carefully. The most important part of your cylinder head is, as per Fig 6-3 and Fig 6-4, the area 1 inch before the valve seat to 1/2 inch after it on the intake and vice versa on the exhaust. Be aware that what you think is needed may not be what is wanted. There are a lot of little wrinkles and nuances in porting that only experience and frequent use of a flow bench can teach. If you are using factory production-line heads and you do not, or cannot, spend a lot of time porting them, the good news is that there is an option.
Pocket porting and attention to the short-side turn will, while sensible street cams are employed, net about 80 to 85 percent of the potential power increase possible. Only when the valvetrain lifts the valve significantly above the 0.500-inch mark will a full porting job show big (as opposed to small or moderate) increases over a pocket porting job.
As the flow curves on these these pages show, the effect of extensive porting only pays off significantly at lifts above 0.450 to 0.500 inch. Prior to that, the seats and the valve pockets/ short-side turn have the greatest influence.
It’s tempting to carve out the space between the pushrod holes as soon as you get hold of the grinder. However, you should consider that this section of the port is already a straight shot into the cylinder head. It’s close to 100 percent efficient, and until the valve’s flow is substantially improved, the pushrod pinch point is not a flow impediment. Sure, at full valve lift it may cause a little flow loss, but remember the valve is only at full lift once in a cycle. It’s at half lift twice, so what happens at half lift usually is more important.
In addition to flow efficiency, swirl is also important, especially for a good all-around street performer. Swirl can be generated or lost depending on how the port is shaped. The first point to be aware of is that virtually all production small block Chevy ports have “port bias” in the throat or bowl area. Fig 6-2 shows the bias angle of a typical small-block Chevy intake port. Don’t attempt to straighten this out. Instead, grind the port to emphasize this bias.
Another factor to consider is that the guide and valve stem take up room in the port and effectively cut the flow area. To offset this, the port needs to be widened around the base of the guide boss at the bottom of the port (Fig. 6-6). Applying the techniques described here to a full-race port spec typically takes about 100 hours. For a set of heads like this, when used on a 350 with an 11:1 CR, the best I have seen on the dyno is 518 hp and 462 ft-lbs. The cam used here was a short race Comp Cams single-pattern 285-2 solid roller with the lobes on a 108-lobe centerline. Given a 310 seat duration cam about 0.650 lift and a 14.5:1 compression, a set of heads like this should allow a ported Victor Jr–equipped 355 to make about 560 hp.
But as good as all the foregoing may be, let us not forget the amount of work involved. A hundred hours can only be justified if there are no other castings available. But there are. Remember that Vortec heads have been around since late 1995. These will port up in a third of the time and show better results to boot. Then, there are the aftermarket heads that we will deal with later. The ones I have chosen to show this time around will port up in less than 15 hours and, with experience, some in less than 8, while producing not just good, but truly outstanding results.
Port Re-Shaping Techniques
At this point, we can start to look at the actual techniques necessary to rework ports and chambers. First, in almost all circumstances except the combustion chamber, the surface finish should not have a high polish. For the most part, you need only use one or another of the carbide cutters shown in the “Porting Supplies” sidebar on page 70. Any of these plus a steady hand can be used to do 90 percent of the work on the heads. Why? The form accounts for 98 percent of the success of a port’s capability. What you may find, though, is that controlling a carbide to get the final form is a little beyond the capability of a novice. This is where the cartridge rolls come in. A coarse-grit roll, say 80, or even 60 grit, can be used more effectively to achieve the final forms being sought.
However, for novices, a point of concern is blending the ports and chambers into the valve seat areas. On the chamber side, the way to tackle this is to use an old valve and cut it down. Working on the port below the valve seat presents a similar, if less difficult, problem. Painting the seat and the area on down into the port a little way with engineer’s layout blue helps. When grinding in the throat avoid getting any closer to the lower edge of the seat than 1/16 inch.
Once all the cutting and grinding is done, the finishing touches can be applied using an emery roll. These can be had, at a very competitive cost, from Dr. Air, as discussed in the sidebar “Porting Supplies” on page 70. Normally, you will use three or maybe four 80-grit emery rolls per cylinder. To economize on rolls, do essential work first, and if they are not worn out use the rolls to do the finer finishing work. This usually means doing the seat area first and then working down into the port or up into the chamber. Polishing the chamber to a relatively fine finish is a good idea. Having a fine finish here cuts heat conductivity and reduces detonation-inducing hot spots.
Understanding that the seats in the head are important is only half the battle. The shape of the valves is equally important. With stock valves, there is not a lot we can do except basic preparation. This involves blending the back face of the valve into the seat on both the intake and exhaust. On the exhaust valve, blend the top face into the margin using a generous radius. Fig 6-5 shows what is needed. Don’t skip this operation!
Inspection of the exhaust ports reveals one port in each head (except aluminum Corvette heads) has a heat riser cross-over passage that communicates exhaust to the heat passage in the intake manifold. This, in terms of flow, looks pretty ugly but, in reality, has little affect on flow. The exhaust valve seat, for these early cast-iron factory heads, should be cut according to Fig 6-7. This is a simple form that works well and can be done by most machine shops with even the most basic seat-cutting equipment. If we are porting Vortec or aluminum Corvette heads, an exhaust seat with a generous radius under it to blend into the rest of the port is the way to go. Exhaust seats/ports like this are used on most high performance aftermarket heads. This offers a distinct advantage if the rest of the port, especially in the guide boss area, is shaped to work in conjunction with a radius design.
Three factors are important on the exhaust port, especially when only pocket porting is being done: the short-side turn, the port bias (as this strongly influences the high lift flow), and the area at the base of the guide boss.
The exit at the manifold face is not a critical area until a refined state of port development is reached. Just as with the intake, the actual body of the exhaust port can come off the short-side-turn seat area more abruptly than it does on the long side on the long-side turn. If the short-side area of the seat flows too much, it causes a highspeed- flow interference issue on the long side. By deliberately reducing the flow efficiency at the seat on the short side, the amount of exhaust exiting here at the mid- and high-lift is reduced so the long side is allowed to work much better. However, once immediately past, the seat area shaping of the short-side port floor significantly influences bulk flow of the exhaust port. If you stick to the form shown in Fig 6-7 things will work just fine.
Compression: The Budget Racer’s Big-Power Ticket
Pay attention here, or it will be the downfall of your quest for best torque and HP from your engine. Once the minor to all-out porting work is done, it will be time to consider what combustion chamber volume will be required to achieve the desire compression ratio. Before arbitrarily deciding on the compression ratio your engine might need check the cam chapter (Chapter 7). From what is discussed there a more informed decision on the cam and compression ratio can be made.
Here, an explanation on achieving cam event and compression compatibility is warranted. Taking into account the fuel octane to be used there is a certain minimum compression ratio (CR) for any given cam duration if the best torque and HP per cube is to be achieved. If the CR drops below this minimum, it becomes better to choose a slightly shorter cam as the combination of a shorter cam with a slightly-lowerthan- optimal CR being used will produce a better power curve than a longer cam with the same CR.
This is not so noticeable with moderate CRs and cams in the 250- to 275-degree (off the seat duration) range, but as the cams start to fall into the racier category, it becomes very important. This factor is one of those parts compatibility things so often alluded to but rarely defined.
Once a cam decision has been made, you will need to establish just what it will take to get that ratio. Here I should point out that, assuming the fuel octane is there, having a CR higher than the cam spec calls for is good, but having it lower is not. In other words, assuming detonation is not a factor, there is hardly a situation where too much CR is a problem.
After consulting Chapter 7 to establish what CR is needed, it’s time to establish what it will take to get it. The first move is to establish the existing CR. To do this, you need to measure the combustion chamber (in cubic centimeters). You also need to make a provisional choice of piston in terms of crown configuration. Remember, a flat-top piston has many advantages in terms of results, weight, and cost. If the CR you are shooting for needs to have a raised crown piston, go for the minimum possible. The best combination is almost always achieved with the smallest chamber in the heads and the least amount of piston crown rise. Using too much of a raised crown on the piston together with many early-style heads with the low plug placement can mask the plugs. This can really inhibit the combustion process and the result is a poor output.
Since getting an adequate CR is sometimes a problem, adding cubes is a great help toward making more compression with a flat-top piston. It costs money to mill heads to get compression, and money spent here would go about 50 percent of the way toward the cost of a longer stroke crank that, often, will ultimately do the same thing for the CR.
All the foregoing leaves us having to machine our factory production cylinder heads as much as possible to minimize chamber volume.
Unfortunately, there is a milling limit imposed by the proximity of the intake valve seat and the cylinder- head face being milled. As the head is milled for compression the face gets closer to the intake seat until the face and seat actually meet. At this point, further milling also cuts into the valve seat. Take a look at your heads, and you will see that it won’t take much in the way of machining for the head face to cut into the valve seat on the shallow side of the chamber. Depending on the position of the seats, the coming together of the head face and seat usually occurs, on stock heads, when 0.030 to 0.050 inch is milled from the head face.
With closed-chamber heads, every 0.010 inch machined off drops the chamber volume by 1.3 to 1.4 cc. Flat milling (as conventional head milling is called) of heads then leaves us with chambers at best 4.5 to 7 cc smaller. What this means is that flat milling usually only gets the heads to the 60-cc chamber volume point. Some heads get machined as low as 58 cc, but don’t count on it. Volumes around the 60-cc mark are fine for a sane low-buck street 350 with flattop pistons in flush to the top of the block. This, with a 0.038 Fel-Pro gasket and typical 4.8-cc valve cutouts in the pistons, will net between 10.4 and 10.6:1 CR.
If more compression, say 12.5:1, is needed for use with a race cam, then the total chamber volume (including head gasket volume etc.) needs to be reduced by a further 12 cc. Let me tell you now that won’t happen, but we can, by angle milling the heads, get more than halfway there.
Angle milling is our alternative to conventional flat milling. By angling the heads at about 1 to 1.5 degrees, virtually zero metal is taken off the intake port side of the head and a maximum on the exhaust port side. By angle milling, the chamber can be reduced in volume to a far greater extent. Ultimately, the limit to angle milling the heads is set by two factors: the thickness of the outside edge of the casting (1/8-inch minimum) and the head face meeting the spark plug holes.
I have cut 186-style casting and achieved 53-cc chambers for an 11.7:1 CR with flat-top pistons, but be aware that heads machined this much are prone to cracking.
Angle milling raises the question as to whether we can do this operation without re-drilling or re-spot facing the bolt holes to bring them back true to the head face. For the amount we’re going to angle-cut the heads, the answer is that it’s best to do so but not 100 percent necessary.
Another potential hang-up with angle milling is that the longer bolts on the inside of the heads can hang up on the side of the bolt holes toward the top of the casting. This interference must be remedied or correct torqueing of the head bolts will not be achieved.
The first step toward fixing the bolt problem is to use some Moroso offset head-to-block dowel pins. These push the heads farther up the block face and give better manifold alignment later during assembly. They will also reduce or possibly eliminate the need to remove material from the long bolt holes. These offsets are available in 0.030- or 0.060-inch offsets. I have found that for the most part a 0.030 offset gets the job done.
To determine approximately what may need to come off the head faces, your first job will be to “check lap” the valves to see that they will, in fact, seal up. If the valves don’t lap in virtually right away, your valve job has not been done properly, so take it back to the shop that did it and have it rectified.
With the seats OK for use grease up the stems and seats on the valve head and install the valves. Next set the heads level on the bench using a spirit level. From a graduated container, you can now pour windshield washer fluid into the chamber. Doing all this to establish what CR can be achieved and how much needs to be machined off may be something you can side step. An increasing number of machine shops are becoming performance orientated and this could make life simpler. All you need to do if you are dealing with such a shop is to take your heads in and tell them what you think is needed in the way of chamber volume and they will a) advise you if this can be done and b) check the volume at interim points during the machining to establish when the required cc has been achieved.
CR Increase Versus Cost
At this point it’s time to tally potential costs of doing our CR business. Angle milling costs a lot more than flat milling. Not only is the setup time about 50-percent longer than for flat milling but we also must include setting up the head to machine the intake manifold face back to the correct angle with the head face. All this means the cost of angle milling can exceed the price of a 3.75 stroker crank which, with flattop pistons and a 60-cc chamber will net about 11.5:1 or 12.5:1 with about 1/8-inch raised piston crown. What we are discussing here is relevant to any pair of heads that you may have stripped and modified, be they factory or aftermarket. After all the porting and machining has been done the heads can be readied for assembly.
At this point I need to introduce you to a CR solution using aftermarket heads. There is good news is this area–namely that they are available with chamber volumes as low as 49 cc. With a flat top in a 350 this would give about 12.3:1 compression.
Buying pro-style head cc’ing equipment can be a little expensive, and as just stated, may not be necessary unless you are contemplating doing the job repeatedly. With the ratios we’ll be dealing with, most commonly 10 to 13:1, a graduated burette is nice but not totally necessary. Power House tools has an economy cc kit (part # 4975). This comprises a head plate and a tall graduated beaker. If you want to upgrade to a pro-style setup (part # 4974), you get a nice 100-cc burette, a stand to hold it, and the head plate.
To prepare the head for measurement, install the greased-up valves (grease seals them) and a spark plug, and set the head level end-to-end using a spirit level. Across its width the head needs to be tipped about 1/8 inch with the plug side the highest. Now grease the plexi-glass head plate and place it over the chamber with the fill hole at the highest position so as to best allow air to escape while filling. Whatever the burette reads when the chamber is full is what you have. Add this to the cc contained in the block, piston cut-outs, and the head gasket and you are ready to calculate the CR.
To find out approximately what needs to come off, set the head level for flat milling or at about 1 degree (high on the plug side) if angle milling. Now fill the chamber with the amount of fluid to represent the volume needed for the CR required. At this point, you will need to measure how much the fluid is down from the head face. This will be a little problematic because when the end of the dial caliper approaches the fill fluid it will jump up to meet the end of the dial caliper. This means a little judgment must be exercised when making this measurement.
Cylinder Head Detailing and Assembly
What we are discussing here is relevant to any pair of heads that you may have stripped and modified, be they factory or aftermarket. After all the porting and machining has been done, the heads can be readied for assembly. Your first job, using a fine round or half-round needle file, is to remove all the sharp edges from around the combustion chambers. At the time the valves were check lapped they should have been numbered and placed in a 2 x 4-inch wood block suitably drilled and numbered to accept the valves.
At this point, the heads and everything going into them should be thoroughly cleaned. Spray everything down with Gunk and go through the guides with a rifle-barrel brush. Next, brush everything else with stiff bristle brushes until all signs of dirt and debris are gone and then hose everything off.
Next, blow off the water with an air line. If you intend to paint the heads, now is the time to do it. Here I recommend using brake caliper paint as it stands up to the heat around the exhaust port better. Be sure you degrease the heads with lacquer thinner or the like before painting. Also mask the areas that need to stay as bare metal. After spray painting the heads place them in a warm environment (hot sun, warm oven, etc) until the paint is good and hard then (and only then) WD-40 the machined surfaces to prevent rusting.
Using a high-pressure lubricant, such as moly grease, smear the valve stems and the guide bores. Don’t let there be any real excess on the intake valve as this grease will wash off and get on the spark plug. A little will burn off right away but a lot won’t.
At this point, you can check the installed spring height that your combination of parts will give. Don’t forget that the valve seats may be lower in the heads than stock, so the installed height of the spring will be greater. It is very important that the spring force produced when the valve is on the seat is as per the cam manufacturer’s specifications. Fail here and the valvetrain can experience premature valve bounce. The stock spring height is typically 1.7 inches, but your choice of cam and the springs required to run it, may call for 1.750 or even 1.800 inches. In some cases where a bigger cam is used, the spring bases may need to be machined deeper (one more money absorbing op).
Measuring the installed spring height is best done with a spring height micrometer, but a passably accurate job can be done with a dial caliper. Each spring station will require shimming to give the correct installed height. Generally, almost all heads will need something in the order of a 0.030-inch shim under the valve spring.
If the cam you are using calls for a dual spring installation, a spring locator or spring cup will be required to stabilize the base of the spring, so it does not walk around when in use. Spring locators/cups generally have a base thickness of 0.060 inch. If more shimming is needed to get the correct spring preload, install the shims under the spring locators/cups. For most of the applications, we are dealing with here getting the seat preload absolutely dead on is overkill. If the spring height is within minus 0.020 and plus 0.010 things will work out just fine.
However, the seemingly wide height tolerance just quoted does not mean we can skip the height check or ignore setting it right. Incidentally, if you are going to do the job like a pro, each spring needs to be checked and possibly detailed. Just how much will be needed will depend on the type and quality of the spring, so be sure to read how to prep your spring package in Chapter 7. The last point of possible problems is interference. Check that the bottom of the retainer does not run into the guide seal and also that at full valve lift the springs do not coil bind.
Once the heads have been assembled, bag them in a plastic bag and set them aside ready for installing on the rest of the engine.
Porting 186/041-Style Head Castings
The porting on these heads is straightforward enough given the guidelines set out elsewhere in this chapter. The longest job is carving out the excess material that resides in the bowls and around the base of the intake valve guide bosses. Be prepared for a lengthy haul even with a carbide.
Let’s cover some of the pertinent points at the manifold face. Don’t be tempted to match the port at the manifold face with a large port gasket. It serves no useful purpose and can, as often as not, cut performance. I recommend using a Fel-Pro intake gasket part # 1204 as a template. As for the rest of the port, cut it using the guide lines given throughout this chapter. My experience is that, armed with the information given, most novice porters will cut a respectably good intake port of about 225 cfm.
As for valve sizes you can, if the cash is really short, stick to the 1.94 and 1.5 combination, but that is only practical if all the guides and the valve stems are good. If valves and a guide job are called for, then it’s a 2.02/1.6 combo you should work toward.
Going the big valve route though is not without its problems as doing so increases the valve shrouding. So why don’t we simply grind a chamber shape to minimize shrouding? Simple: the heads are more likely to crack!
Modifying the combustion chambers of the heads in question is one of the more critical areas if any kind of street reliability is to be had. These heads have a propensity for cracking between the intake seats and the water jacket in the area shown in Fig 6-9 especially if high compression ratios are to be used. Do not grind away too much metal in this area. Not only does it increase the possibility of cracking, it also has little positive effect on the airflow achieved. However, grinding 1/2 to 3/4 inch nearer the spark plug does increase flow, and that area is solid cast iron so you may as well go for it.
To keep the cracking situation to a minimum I recommend that the tool used to sweep out the chamber has at least a 1/8 corner radius.
Now is time to deal with the exhaust ports. To modify these use Fig 6-7 as a guide toward producing an effective exhaust port. Doing so should net about 170 cfm at 0.500 valve lift. Given a flow bench to reference the work and adding a high dose of experience can net a port that delivers as much as 195 cfm at 0.500 valve lift and as much as 210 at 0.700 lift. See Fig 6-10 for the results.
Porting L98 Corvette Heads
The L98 factory aluminum heads are, at 22 pounds, light and thin (iron heads are typically 47 pounds). Because of the effort to save weight, these heads are not as tough as their Bowtie brethren or any of the aftermarket heads. Also note that aluminum corrodes with age especially if the anti-freeze mix was not maintained properly. They can be very effective for specific uses if you can find a good set. However be aware they won’t last any length of time over about 11:1 CR.
The flow of these heads in stock form is really no better than a typical early factory performance iron head. As a straight bolt-on (and with the appropriate self-aligning rocker), these heads have little if anything to offer. However, if you are looking for a cheap set of light heads for relatively easy porting, you might have something worthwhile. If the intent is to produce a true street combo where output from a little over idle is the goal and peak RPM is not much more than say 6,000 for a 350 (and correspondingly higher or lower for other displacements) then these heads, when ported, may be a budget answer for your needs.
Because they are aluminum, these heads can be cut at about three times the rate to cast iron, so porting is much faster. Second, the reason they make good street heads but not good race heads is that the ports cannot be made too much larger without finding water. If you are looking for heads with a smaller chamber volume, these heads are typically around 58 cc (64, 68, and 76 are common chamber volumes) but milling is limited to a flat mill of about 0.020 because the deck face is relatively thin.
With the limitations just mentioned in mind, let’s start with the combustion chambers. The first step here is to remove the casting gauging points between the spark plug and the head face. This together with a chamber sweep around the valves (best done by your machinist) increases the chamber volume to about 60 cc. This volume together with a decked block 350 build using flat-top pistons will give a 10.8:1 CR. If you are building a 383 then for a 10.5:1 CR, a dished piston having about a 13-cc volume will be needed.
These heads normally have castiron guides and these guides more than likely need to be re-sized or replaced. This means you may as well go whole hog and install larger valves. The seats limit the maximum valve sizes to 2.00 for the intake and 1.55 for the exhaust. I have, in the past, cut down 2.02/1.6 valves for this, but some valve companies may well have off-the-shelf valves these sizes. I have flow tested with stock valves but never used any stock valve Corvette heads on an engine. With suitable valves on hand all the time, it never made sense not to go the 2.00/1.55 route, and that is what I would recommend here.
The L98 ’Vette head’s greatestasset is its high swirl and intake port velocity. To get optimal results, you should not detract from those assets. Though small, the stock port shape is not that bad for that era of production heads. Its principle shortcomings are casting flaws and small cross-sectional areas. The outside walls (see Fig 6-6) are the busiest areas, and consequently,are the place to work on. Using Fig 6-6 as a guide, work on wall “A” and its approach into bowl area “B” because this is the highest flow region and the most crowed as far as the air is concerned. Keeping the strongest flow on this side of the guide boss maintains this head’s strong swirl characteristics. Next blend area “D” and just clean up the wall leading to area “C.” Work area “C,” so that it blends into the underseat part of the port in a smooth fashion. At this point, rework the short-side turn into a radius as large as can be accommodated by the material present. These moves, with the bigger intake valve, should net the results shown in Fig 6-11.
The exhaust ports on these heads are relatively easy to do and deliver good results in the process. The point that must be kept in mind is that at mid- and high-lift the flow exiting the cylinder is from the center on out. This, in turn, means the port bias is important if good flow is to be realized at these higher lift values. Once this has been incorporated into your thinking, the rest gets easier. Just pay attention to the short-side turn and cut the rest of the port as per Fig 6-7 and all should work as intended.
Porting L31 Vortec Heads
In the absence of a flow bench, Vortec heads are about the most goof-proof castings to rework and get good results. Fig 6-12, the stock L31 head is considerably better than the “Fuelie”- style heads we find ourselves working with if factory heads are the order-of the- day. Because of the exceptional casting quality coupled with a highly effective design in terms of flow, porting these heads is about as simple as it can get. That’s the positive side of things. The negative is the factory did such a terrific job in the first place, so there are only minimal gains to be had from pocket porting the intake.
The exhaust is a different matter. Because the intake flows well, the smaller deficiencies we see in the exhaust flow of the Vortec heads have a bigger negative impact on power output. For a production casting, the exhaust ports are pretty good, but they can be improved quite a bit.
It’s all work for sure, but the good news is an exhaust port rework on a 375-hp motor can show an increase of up to 20 hp, and that’s not too shabby considering you could get all the exhaust ports done in about 4 hours.
Because it is so easy to achieve professional-looking results, you may want to re-work all the ports. To do this, just take some 80-grit emery rolls and go over the entire port surfaces for a pro look. While doing so, pay attention to the pushrod pinch point as this can usefully be widened to bring the minimum port area up a little. This cleanup operation will start to pay off above about 0.400 valve lift. At about 0.600 lift, it can be as much as 5 to 7 cfm more.
The only way to see a significant increase from the intake in the 0- to 0.400-lift range is to replace the stock intake with a 2.02- or better yet a 2.05-intake valve.
The stock seat geometry is, like the rest of this heads design, very effective. Unless the seats for the bigger valve are done in an equally effective manner a lot of the extra potential of the bigger valves will be lost. Entrust your Vortec head seat work only to someone capable of producing an accurate and flow effective seat.
Just installing the bigger intake valves does little to increase overall flow. The bottom line here is that if you are going to make the most of bigger valves the port needs to be reworked also. Again, if you re-work the intake port as per the guidelines of Fig 6-6, good results can be had. As for the exhaust target use the form shown in Fig 6-7, but leave the under-seat radius as stock. As for overall results, you can expect to achieve flow figures as per Fig 6-12.
Because the combustion chambers have a lot less shrouding than most production head castings, the Vortec heads have better flow potential in the low- to mid-lift range, both on the intake and exhaust, but is partially penalized at lift values above about 0.500. This, and a relatively small intake port volume of about 176 to 178 cc, ported (170 cc stock) means good flow and port velocity. This, in turn, offers the potential to build a really wide ranging torque curve that produces strong HP everywhere, but it assumes the rest of the engine spec is compatible. A 10.5:1 350 peak torque number in the 445 to 460 range is possible along with power numbers in the 465- to 475-hp range.
A few words more on the subject of Vortec heads before we go on to aftermarket offerings. Please remember that the Vortec heads had a different intake manifold bolt pattern and require, in most instances, a Vortec-specific manifold. Also selfaligning rockers are used rather than guide plates, so be prepared to purchase another set of rockers if you don’t have the appropriate ones.
When I wrote the first edition of this book, World Products made the only low-cost aftermarket heads, and these were cast iron. During the late 1990s, a shakeup among some of the leading lights in the cylinder head business started the snow ball rolling. Starting with Dart’s Iron Eagles, we find that by about 2005 there were more aftermarket heads than you could shake a stick at. Some are very good, most are good and some are, well, let’s say you won’t see me using them any time soon.
Let’s start with the World Products heads. At one time, I used a lot of these heads for my small-block Chevy builds for two reasons. First, they were the only game in town and second, this meant I got a lot of practice porting them to fine tune what worked and what did not. By 2000 I could build a relatively cheap, simple, no-drama 600-hp road-race engine using these heads.
Basically World’s heads fall into two categories: Stock Replacement (SR series) and the Sportsman series intended for high performance. The SR heads were originally intended to satisfy a market for heads to replace the later lightweight and thin highly crack-prone castings GM was producing from the mid to late 1980s on. The universal fit called for meant the original SR heads had small valves, but these heads were so well received that they felt justified in producing the SR Torquer, which was available in 1.94/1.5 or 2.20/1.6 valve-size form.
In unmodified form, they are okay but not intended for high performance, so one should not expect too much of them. That said, they port up surprisingly well, and if you come across a used set in good condition at a give-away price, they might be a real budget HP deal. I have ported a couple of sets of the biggervalve SR Torquers, and the final dyno numbers actually looked pretty good. Both sets were used on relatively low compression (9:1) truck motors with short cams (around 260 degrees advertised), and both sets made better than 430 ft-lbs on a 350.
I also built a Street Stock dirt-car motor that, in the cylinder head department, called for either stock factory iron heads up through to about 1985 or 1.94/1.5 SR Torquers. I opted for the Torquers here. The head chosen was the pivotal point of the build. With the highly constrictive rules, the front-running competitors were, according to the chief Tech man, finding about 335 hp max. After a very labor-intensive build, I produced a class-legal 368 hp. Now that may not sound like a lot of power, but the limitations imposed by the rules were hardly conducive to output. Things like a 0.45-valve-lift max. Absolutely no porting on the intake runners of the stock iron Q-Jet manifold. A stock Holley 650 or a stock Q-Jet carb,and the list goes on. Given enough time, I am sure I could have bumped that 363 hp number to 385 or maybe a tad more. Not that it would have made any difference as, with the hard spec tire called for, it would not, at any point around our local track, hook up anyway.
As far as World Products heads are concerned, my main push is with the Sportsman II heads. In as-cast form, they used to be the hot ticket for an easy bolt-together build that produced good results, but many later designs have overtaken them. If you find a set of used ones in good condition (they are almost indestructible), buy them. They are typically worth 40 hp over almost any stock casting other than the Vortecs. As for porting, they can deliver good results but because the casting is, what might these days be called “old school,” the work is time-consuming due to the amount of metal that needs to be removed. Figure that pocket porting and slimming the guide bosses, which produces good results, will take 4 to 6 hours. If you follow the porting rules given in this chapter, you can expect results as per Fig 6-13.
Aftermarket Performance Cast-Iron Heads
Since the first edition of this book I have concentrated on three brands of heads because the excellent results I am getting warrant doing so. With that said let’s look at the options open to you among the heads that I have racked up flow bench and dyno time.
By employing what are essentially better and probably more expensive casting techniques Dart, Engine Quest (EQ), and RHS have produced heads that have sufficient casting-form and surface-finish accuracy to set new bench marks for heads with as-cast ports and chambers. Not only are the forms used far superior to those available in the 1990s, but the surface finish is also far better. As a result, these heads have made life for the home porter so much easier that porting, between the old and new, is as different as night and day.
Out-of-the-box flow figures are as good as pro-ported heads from just a few years back. Because the design of the port and chamber form is so good these heads are far more sensitive to minor casting surface flaws. To better understand how this works, consider knocking a couple of dings into the intake port of an early-production casting. Because, it was already bad an extra unwanted imperfection made little difference to overall flow. Now imagine doing the same to the intake port of a $10,000 Cup Car head. What do you think that would do to the flow? If you suspected it could cost 20 cfm you’d be right. This also applies to our new-generation precision-cast heads. Because the ports are good in the first place, a lot more air goes through them and a seemingly minor flaw, when removed, can bring about a greater increase in flow than you can expect from a lesser casting.
For those who want to try their hand at porting heads, this is really a giant step toward the easy acquisition of pro-porting results. Just so you understand this point, let me be sure I have made myself totally clear: to achieve really effective results, you don’t need a lot of fancy porting equipment, a flow bench, or a lot of experience. Instead, you need just average dexterity, a cheap die grinder, and some porting supplies.
Port and Chamber Volume Selection
Before you can start on any cylinder head project, you will need to make some decisions as to what port and chamber volumes are likely to be best suited to your application. First, all of the iron heads we are looking at here will run a 10:1 CR on premium fuel without fear of detonation unless the engine is running too hot or the timing/mixture is off the mark. So, unless there is a good reason to use less compression, select a piston crown and a chamber volume combination that will give the required CR. As for the intake ports, please understand that bigger is not always better. We talk about port volumes here, but it’s actually the port cross-sectional area that is the influential factor. The problem is that a small-block Chevy’s intake port area varies quite a lot down its length from the intake manifold face to the valve. Since all 23-degree ports are fundamentally similar in length, this makes it easier to consider port size in terms of volume rather than cross-sectional area. To make a choice here use Fig 6-14.
Basic Porting Results
Here, I will describe the results seen by doing a basic porting job on EQ heads. However, the results seen with the Dart and RHS heads are, for all practical purposes, about the same. What this means is that the price is the deciding factor when choosing between these brands. You can be sure that some big parts house will have one or another of these heads on sale during any 12-month period. To reference all your choices in this area, check out the specs of the heads in the sidebar “Early Production Iron Performance Heads” on pages 63-64.
Having made your choice of castings, take them into your workspace and closely inspect them. It won’t take long for you to appreciate the fact that in terms of shape 98 percent of the work is already done for you. In terms of finish quality, these heads are probably about halfway there before you ever start. To get results, the rules are simple. Just apply what was discussed earlier in this chapter. Since most of the work will be done before you start, you will find it is more like detailing rather than outright porting that you will be doing. Typical results can be seen in Fig 6-15.
As for output, a set of heads like this can deliver the airflow required for 540 hp for a flat-tappet 12:1 engine and as much as 585 hp for a roller-cam-equipped engine.
Iron Heads Compared
Here is my current experience with the three main players in the high-performance iron head business. First, the RHS Pro Action heads. At the time of this writing, I am still building experience with these RHS heads and so far the results look really good. Out of the box, the midrange flow on these heads is a little weaker than either of the other two we are considering here, but the topend flow is a little stronger. Although this may be a minor factor in nature, it is something to take into account if the build is to have no more than, say, 0.500 valve lift. So far, all my experience with these heads has been with valve lift figures in the 0.600 to 0.625 range. Like the other two sets of heads under consideration here these heads, with basic procedures, port up very well.
DV Proven Power Heads
Cost-conscious circle-track race classes are the driving force behind the production of performance castiron heads. Both production numbers involved and the intensity of the competition has resulted in the development of genuine, low-cost, as-cast high-performance heads. To put their performance capability into perspective these heads, with little or no further porting, would have produced comparable results to those on a $40,000 1980 Cup Car engine.
Canfield, Edelbrock, and Dart have all, during my dyno testing, proven to be very strong performers when used with an appropriate combination of compression, cam, valve train, and induction.
Dart’s Platinum Iron Eagle is next. These heads benefited greatly from the use of an intense “wet-flow” development program. My dyno tests have shown this wet flow technology to be worth over 20 hp on a nominally 480 hp test engine. These heads, either as-cast or with basic porting, have shown some fine results. Like the other two head designs featured here, these heads port up very easy. Just before going to press with this manuscript, I ported a set of 230 cc runner versions of these heads (2.08 valve). The finished result was 315 cfm for the intake and 223 cfm for the exhaust at 0.700 (seven hundred thousandths) lift. To put those figures into prospective given a mild race cam, 12.5:1 compression and good race single plane induction system that’s more than enough air flow to top the 600 hp mark from a 383.
Of the group here the heads I have the most experience with are the Engine Quest EQ 23 heads. For around $500, bare per pair, these heads are a great deal. The casting finish is definitely modern era but just shy of being as good as the either Dart or RHS offerings. But finish is far less important than form. From my dyno testing experience with these heads in both the 180- and 200-cc versions, I have concluded they have what it takes in terms of swirl, combustion efficiency, and wet-flow characteristics. As an interesting aside, there have been several highly regarded professional engine builders who have lost bets by underestimating the power production capability of these heads.
As well as being good out of the box, these heads port up easy (with 2.08/1.6 valves 301 cfm on the intake and 207 on the exhaust at just 0.600 lift) and can be done by a rank beginner over a weekend. Since their introduction in 2006, these heads have been showing championship winning form on many circle tracks.
I suspect that many of the iron heads discussed here will get a basic porting job done on them, bringing up the question as to which ones port up the best. Having gone down that road, I can tell you that after porting the results are so close that it’s a virtual three-way tie in that department. If you are looking to port one or another of these head sets, then price at the time you intend to purchase should be the deciding factor.
Without a doubt, there are some really good heads that have become available since 2000. I have run quite a few pairs of Canfield heads, a couple of pairs of Edelbrock heads, and a ton of Dart heads in as-cast and subsequently ported form. In addition to this, I have run CNC-ported Dart and AFR heads with really good results. However, only one model of CNCported head falls into the price range set for this book: AFR’s 195 Eliminator street head.
All of the heads I have used over the past ten years have been the result of recommendations by reputable engine builders who have had successes with the heads concerned and have recommended I try them. This makes life easier for me as magazines are never in a rush to run a story on a product that does not work. What they really want is something that produces results good enough to get excited about. Well the advice I got from my pro engine builder friends saved me for the most part, testing performance equipment that might have otherwise been indifferent. Let’s start with the Canfield heads.
For a 350 or a 383, I have favored the 195-cc version of the two port volumes offered for Canfield heads. They have produced good results in out-of-the-box form and responded well to basic porting. With a singlepattern flat-tappet Comp Cams cam (276-3 profile on a 108-lobe centerline angle) 430 hp and 440 ft-lbs is on from a street-driving 10.5:1 350. With a hydraulic roller cammed 383, this goes up to 470 ft-lbs and 470 hp. From engines of a simple bolt-it-together spec, these are good numbers. But these heads can be basic ported over a weekend and, in round numbers, that’s typically good for 25 to 30 hp. When ported, these heads will top the 515-hp mark along with about 485 to 490 ftlbs of torque without a huge expenditure of cash. A Comp Xtreme 224/230 at 0.050 on a 106-lobe centerline angle and 1.6/1.5 rockers does the job in the valvetrain department for this kind of output. Couple that to a Super Victor intake and a good 800-cfm carb, and you are in business. Also noteworthy is that I have seen very good results on a 350 equipped with an Edelbrock Air Gap Performer intake.
Canfield also makes a 220-cc version of their small-block Chevy head. These are good as-cast for racier 383s and bigger engines. Ported they can really deliver results. At 12.5:1, a solid roller 383 can be coaxed over the 600-hp mark without too much drama. Although a little outside the scope of this book, I did do a set of these to an all-out spec that went on a not-so-budget 13/1 440 inch small-block that went well past the 700-hp mark.
Edelbrock offer a wide range of options on their street heads, and I figured it would be a full-time job for quite a while testing them all. It might be nice to do just that, but the time and budget just aren’t there. My main test objectives with the Edelbrock Chevy heads I have used are for street performance where true low-speed street output is called for. Both the emission-legal Performer and the Performer RPM heads have produced power curves on either a 350 or a 383, which did just that. As they come out of the box their 170- cc intake runners produce strong dyno numbers in the 1,500- to 3,500-rpm range but tend to fall off much above that. Spend a weekend porting them, and you will like the results. Doing so makes the ports only about 3 to 4 cc more, and you will like what it does to the top-end output. Essentially, a 383 will pump out about 30 hp more with no measurable loss at the low end.
If you are building a 350, it’s worth noting that these heads don’t come in the smaller chamber sizes. You will be looking at 70-cc chambers for the Performer and 72 cc for the RPM version of such. This means achieving a 10:1 CR is more of a problem unless the build involves more than 350 inches.
I have lost count of the number of Dart aluminum Pro 1 small-block Chevy heads I have used on various mule/project engines. With an appropriate parts combo, they worked well as-cast and especially well after I ported them. Since I am in no rush to fix something that works, I have used ported Dart heads on a lot of my engines because I had done enough of these heads to know where to easily increase flow and, consequently, HP.
In 2006 Dart came out with their wet-flow-developed version of the Pro 1–the Platinum Pro 1. With these later heads, Dart was talking an extra 15 to 25 hp depending on the combination it’s run on. Sounds good, but I needed my own numbers just to establish the value of whatever wetflow development they had done.
The interesting aspect of this test is that the flow of the 200-cc Pro 1, and the later Platinum versions were virtually identical. In this instance, any differences in output would be due solely to the hopefully better wet flow characteristics of the Platinum heads over the originals.
In this instance, the test engine was a 383 with a hydraulic roller valve train. Fig 6-16 shows the results. You can see that some applied wet flow technology worked very much in our favor.
Although I have used all the port runner sizes of Pro 1 heads that Dart offers, my main experience is with the 200 and 215 heads. But before I discuss that let’s talk about their 180- cc heads first. If you are building a street 350 or a 383 that has to have low-speed grunt, these heads work fine right out of the box. They have 500-hp capability but work out best if cammed to give about 480 hp. With a cleanup 500 hp is almost a breeze and can be achieved without compromising low-speed output especially if the build is a 383.
While the 180-cc Darts work very well out of the box or in basic ported form I do have a move that makes for a wider power band and a little more upstairs without a low-speed sacrifice while still delivering a good top end. This works well if you are building a 350 or a 383 that really must be a nice street driver.
Basically, I replace the 2.02 intake valve with a 2.08 valve, cut a high-flow seat and then apply a basic porting job. Using this head, I then spread the cam’s lobe centerline angle by 1 degree from what would have otherwise been optimal then pick profiles for the intake and exhaust about 4 degrees shorter. All this results in the same top end as the smaller valve and longer cam, but with a smoother idle, more torque in the low speed range—and better mileage!
If you are building an engine where you are targeting about 440 to 450 hp, these heads need to be a serious consideration. With basic porting, they are good to 500 very streetable hp on a 383. The top chart on page 84 shows the flow numbers you can expect.
As for large runner heads, I have ported some 230-cc Darts for some serious HP on big-inch small-blocks. Even with streetable cam specs and 10.5:1 CR, these engines top 600 hp with ease and deliver torque numbers of 575 ft-lbs from 440 inches. The bottom chart on page 84 shows the flow specs for a 230-cc head, stock and ported. From these figures, you can see that either out of the box or in ported form the Dart Platinum 230 acquits itself well.
The most likely size of engine that a reader of this book will build is a 383, and that is very much the same for me. That is why I have had so much more experience using heads of 200- to 215-cc intake runner volume. Again, assuming street usage I tend to favor a 200-cc port if I am going to port the heads. If I am not going to port the heads, I tend to favor the 215s. So that you can see how, in as cast form, each size of port volume Dart head responds on a typical budget street driver check out the results in the sidebar “Port Sizes” on page 86.
OK. Let’s take a look at the flow figures for the Platinum versions of these heads. The 200-cc head responded to our flow bench as shown below left.
Using a two-plane intake manifold and a relatively budget valvetrain, such as a flat-tappet hydraulic cam of, say, 270 degrees seat-to-seat duration, you can expect a 10.5:1 383 to deliver 485 ft-lbs and about 435 to 440 hp using these heads as-cast. Port them and 495 ft-lbs and about 475 to 485 hp are yours to be had.
Stepping up to the as-cast 215s for a 383 and using a hydraulic roller of about 240 degrees at 0.050, a thoughtfully built 383 can return some 500 ft-lbs and power in the region of 520 to 530 hp. My best effort to date was a 244 at 0.050 Comp single-pattern hydraulic cam 383 with as-cast 215 heads that made 495 ft-lbs and 528 hp. Ported they will go about 25 more horses than this. The flow for both as-cast and basic ported Dart 215 Platinums is at bottom left on page 85.
AFR 195 Eliminator
The Eliminator from Air Flow Research is our entry-level CNC ported cylinder head. At the time of this writing, I have had experience using this head on 355- to 408-ci engines, and it has produced very satisfying results each time. Introduced in its current form about 2005, this head design has established itself as one of the most successful on the market. In addition to this, it is also one of the, if not the most, cost effective of CNC heads available. In fact, at the time of this writing, it is the only one that comes in at a price that allows it to be used within our budget constraints.
I have used these heads on a 383 build and closely approached the 600-hp mark, yet still had change left out of a $5,500 bank roll. These heads come with 8-mm-stem lightweight valves, smaller-diameter valve springs of much higher quality than you would expect of heads in this price range, plus lightweight retainers. All these valvetrain factors make these heads very hydraulic roller friendly, and in simple terms, that means more RPM on less spring.
For more information on all the heads covered in this chapter go to MotorTecmagazine.net.
Written by David Vizard and Posted with Permission of CarTechBooks