Now we get into the heart of small block power. You can have a killer camshaft, valvetrain, intake manifold, carb, and headers, but if you bolt ‘em to a weak set of heads, you won’t make power. It’s that simple. Conversely, spend your bucks on the best heads you can afford and your engine is destined to make excellent power. But this doesn’t mean buying the most expensive, widest advertised, or even the biggest ports on the market. Always remember the engine is a system of interrelated components, and the one who makes the best power is the guy who figures out how to make all those parts sing in harmony. So let’s dive intowhatmakes cylinder heads so special.
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IRON VS. ALUMINUM
This has almost become a moot point when it comes to making power. In the beginning, iron was all there was for the performance enthusiast. Today, there are more aluminum small-block performance heads on the market than anytime in the history of man. But recently there has been an explosion in iron performance heads that offer a budget alternative to the more expensive aluminum castings.
Strictly from an efficiency standpoint, iron heads should enjoy a slight performance advantage in that aluminum conducts heat much quicker than iron. This means that a certain amount of heat is lost through conduction, which also means a certain loss of cylinder pressure. While this appears to be reinforced by the fact that most aluminum- headed street engines can accommodate a little more static compression compared to otherwise similar iron-headed engines. However, when it comes to ultimate power, there appears to be no clear advantage to iron over aluminum.
While iron heads are usually less expensive than their aluminum-alloy cousins, there are also disadvantages to the cast iron route.Weight is the obvious penalty. You can expect a pair of aftermarket iron heads to weigh an additional 45 to 50 pounds over the front axle. In addition, cast iron is notoriously brittle , and cracks can occur that are difficult and costly to repair. Aluminum tends to crack less often and when it does it is much easier to repair. But don’t let this dissuade you from defecting from the iron cause. If you get a great deal on a set of killer iron heads, go for it.
ANGLE OF ATTACK
All production small-block heads are based on a 23-degree valve angle that was established by Chevy engineers way back in the dark ages of the early 1950s. To maintain production engine interchangeability, that valve angle has only started to change in the last 10 years or so. Cylinder head porters will tell you that the more vertical (closer to zero) the valve angle, the better the airflow potential. This is due to several factors that include creating more uniform flow around the entire 360 degrees of valve circumference. Of course, this also demands that the port be made taller to take advantage of this taller valve angle.
Today, several companies offer taller valve angle heads, the most notably the 18-degree, 15-degree, and SB2.2 heads from GM Performance Parts, as well as the 14-degree iron heads from Pro TopLine. But while alternate valve angle heads offer outstanding airflow, they come at a cost. Budget is not a word commonly used with these heads. The hidden costs are involved with pistons to accommodate the different valve angles along with specific valvetrain parts like rocker shafts that are necessary to make everything work. We only mention all this to get past all the hoopla and the interest in the major airflow these heads generate. It is also worth mentioning that Trick Flow Specialties (TFS) offers an 18-degree head that is more affordable than other heads, while still delivering excellent flow numbers for a small-block head. But we’re still talking about a set of heads that will set you back all of $2000 and require a specialty intake manifold and custom headers.
Assuming that most street engine builders will opt for a set of 23-degree heads, there are dozens of heads to choose from. And within each of those heads are a myriad of options and ideas that are important to the overall engine combination.
The areas of most attention for any cylinder head are the intake and exhaust ports. Virtually the entire cylinder head world revolves around port volume numbers as an easy point of differentiation. Stock small-block heads vary in shape and size but hover generally at around a 170cc intake port volume. Before we get much further, however, we should quantify exactly what we’re really discussing when we talk about port volume. The way port volume is determined is by simply stuffing a valve in the head, turning the head intake port face up, and measuring the volume with a calibrated burette. The problem with this measurement is that if we were to extend the length of the port, the volume will increase, but that would have negligible effect on power. In other words, the port would appear bigger when in fact it was really only longer.
The critical measurement that we should examine is the port’s cross-sectional area. This is best described as the port’s choke point where the flow area is the smallest. Imagine that our intake port is a simple tube. Increasing the length of the tube does nothing to improve flow. However, if we increase the diameter of the tube, flow will increase. Now, if we take that larger tube and constrict it slightly back to the original tube diameter, the flow will probably drop back to something close to the original tube’s flow potential. Now if both tubes are the same length, measuring the volume might lead us to estimate that the larger volume tube would flow more because of its greater volume — mainly because it fits the simplistic “bigger is better” theory that permeates the performance world. As we’ve seen, the flow may not deliver on the bigger is better concept. This leads us back to the concept of port cross-sectional area.
A little experimentation with stock small-block heads reveals that stock heads measure in the neighborhood of 0.9-inch wide x 1.85-inches tall at the narrowest point of the port, which is where the pushrod wall intrudes into the port. This comes out to a relatively small area of 1.66 square inches. We’ll use this as our baseline for comparison with other performance heads to see how they compare both with the port volumes of stock heads and other performance heads. As a point of reference, the original Brodix Track 1 intake port measured a much larger 2.3 square inches of cross sectional area at the same point in the port. Port volumes tend to support the fact that the Brodix head is larger than the stock head, and this is why port volumes don’t exactly lie to use in terms of small, medium, and large port heads. The cross-sectional areas of the smallest point in each of these ports tend to follow the volume numbers.
So why is port cross-sectional area so important? The answer goes back to our pipe analogy, but the reasons go much deeper. When the piston accelerates down the bore with the intake valve open, the pressure differential creates air movement in the port, which generates a velocity in the port as the air and fuel travel from the intake manifold into the cylinder. The smallest cross-sectional area in the head limits the volume of air that can travel past this point. This minimal area also establishes the speed of the incoming air column.
Given this, a small port tends to create a given inlet air velocity sooner in the RPM curve, which can be equated to the peak efficiency point for the port. This also turns out to be the peak-torque RPM point. At engine speeds below this point, the air has not achieved sufficient speed to fill the cylinder entirely. At engine speeds above this max velocity point, the small cross-sectional area physically cannot supply the volume required by the cylinder to make more power. The engine still makes decent power, but once the peak torque point is established, most engines achieve peak horsepower within another 1,100 to 1,500 rpm.
We’ve just wrapped a bunch of variables that affect peak torque and horsepower (like cam timing, intake and header runner length, and a bunch of other stuff) all up in this intake port cross-section concept. The point is that intake port cross-sectional area is amajor player in the torque and horsepower game. For example, a great example for this would be to test a series of intake ports (from 180cc to 230cc ports, for example) across the same engine, while all the other components remained the same. Plotting the torque curves on the same graph would reveal a distinctively progressive series of curves where peak torque increases in RPM. This is an excellent way to visualize the effect of bolting a larger intake port on an engine.
The higher-RPM peak torque figures also point to a better peak horsepower potential. But that does not mean that a larger intake port is always a good idea. Remember, the larger cross-sectional area of the port would require a higher RPM in order to achieve that peak inlet air velocity. Below that point, the slower inlet air velocity would not be insufficient to fill the cylinder. Therefore, torque would suffer. And that’s exactly what happens with a street motor with the combination of a long duration cam and large port heads.
Another way to look at this is that with a given port cross-section, as displacement increases, the peak velocity point occurs at a lower RPM point. Taking this idea a step forward, a cylinder head with a larger cross-sectional area will make decent power without sacrificing a significant amount of torque. Since the non-ported volume of most 23-degree small-block intake ports is less than 230ccs, this occurs rather naturally. Early testing with a 454ci small block by World Products has already generated 610 hp with a set of 220cc intake port Motown heads with an excellent torque curve that made 584 ftlb at 4500 rpm and 559 ft-lb at 4000 rpm. Certainly this engine could make 475 to 500 ft-lb. even down at 2500 rpm.
The net effect of this is that the larger the engine’s displacement, the smaller it makes the cylinder head look. Even though we are talking about displacements equaling a 454 rat motor, the largest small-block head is still tiny in comparison to a rectangle-port, big block head. We measured the cross-sectional area of an intake port in an Edelbrock rectangle port Victor head and came up with 3.75-square inches. This is monstrously larger than any small-block head we’ve measured. This gives a larger cubic inch small-block a decided advantage in terms of torque, and based on the power created by World’s 454ci small block, 600 hp is better than most rectangle port, big-block street engines equipped with a similar-sized cam. It’s possible that there is something to this idea of improving inlet air speed with smaller ports that flow big numbers. A classic rule that has stood the test of time is the best port combines the highest flow with the smallest cross-sectional area.
Before we get into looking at individual heads, it’s important to know what to look for. The bigger is better approach demands going to the bottom of the flow bench chart picking the head with the biggest flow numbers. But all engines push the intake and exhaust valves run through a curve, which means the flow at 0.300 and 0.400-inch lift is also important. Let’s say your camshaft can create a maximum of 0.600-inch lift. Let’s assume the valve actually achieves that lift number (deflection aside). Even if it does, the valve will only do so once in the entire lift curve. The mid-lift numbers (0.200 through 0.500-inch) will be achieved both on the valve’s way up to max lift and also on the way down. If you’re smart, you’ll begin by looking at a cylinder head’s mid-lift flow numbers instead of the peak flow numbers, since these mid-lift numbers will probably contribute more to overall flow (and power) than the peak flow number.
This means you will need to have access to an entire flow chart in order to evaluate the performance of all these different heads. We have supplied a chart that offers flow numbers for a few of the more popular heads from several different manufacturers. The flow numbers were generated at Westech Performance, in Mira Loma, California, on a computerized Super Flow 600 flow bench. All the flow numbers were achieved on the same flow bench run by the same operator using the same correction factors. All these flow numbers were tested at a test depression of 28-inches of water and corrected to standard temperature and pressure.
One thing that you might notice is that some heads appear to sacrifice mid-lift flow in order to achieve those greater high-lift flow numbers. This is the result of a complex combination of factors including port cross-sectional area, valve seat entry angles, valve seat angles, and dozens of other variables that make up the alchemy of cylinder head port flow. We don’t want to minimize high-lift flow numbers, but it’s important to note that the mid lift numbers may contribute as much to overall cylinder filling as the high-lift numbers. It’s important not to ignore the concept that the opening side of the cam lobe occurs at roughly the same time that the piston achieves maximum acceleration, which offers the maximum pressure differential between the cylinder and the intake plenum.
So far, we’ve focused on the intake side of the head, which is really only half the story. The exhaust ports are just as important, since no engine can make decent power if a sizeable percentage of the exhaust component remains in the cylinder. There are plenty of theories that surround the performance of exhaust port flow, especially in relationship to the intake side. The current accepted theory supports the idea that the exhaust port should flow at around 70 to 80 percent of the intake port flow at the same valve lift figure. As an example, if the intake port flows 220cfmat 0.400-inch valve lift, then the exhaust port should flow 176cfm if the exhaust flows 80 percent of the intake at 0.400-inch lift. Regardless of which percentage to which you decide to subscribe, it’s important to remember that the key is to evacuate as much exhaust gas from the cylinder as possible.
Finally, it’s important to give more than passing credit to combustion chamber shape and the effect of the chamber on the combustion process. If you look at the gradual progression of smallblock chambers from the 1960s to today, you can see that the early chambers were bathtub-shaped with deep walls that tended to shroud airflow both from the intake as well as out the exhaust. Today, current chamber shapes favor a more shallow kidney shape intended to improve airflow while also encouraging improved mixture motion. This is difficult to quantify, but the idea is to encourage the mixture to move toward the exhaust side of the chamber so that once combustion is complete, piston movement encourages the residual gas to move in that direction.
It’s also worthy of mention that many of the heads mentioned in this book employ a tight, 64cc chamber. Since large cylinder bores are part of the big-inch equation, you might want to consider opening up the chamber slightly to unshroud the intake and exhaust valves up to the bore diameter to maximize port flow. Cylinder head companies have not started building heads and chambers to specific bore size, so most must assume the smallest, 4.030-inch bore size for chamber wall position. But plug in a 4.155 or 4.200-inch bore and there are measurable flow increases available to the enterprising hot rodder who is willing to take advantage of a bigger bore, beyond just displacement.
We’ll start our look at performance heads oddly with a stock casting that deserves attention. The production iron GM head for the early Vortec engines is an outstanding example of a 170cc intake port that offers excellent low and mid-lift flow that is perfect for a mild 383 or torquey 406ci small block. With the right small cam, a 406 could easily make well over 520 ft-lb of torque with a set of these heads while still being capable of 465 hp. This head is a derivative of the iron LT1 cylinder head used in the Impala SS, and it was also found on ‘96 Chevy pickups. Perhaps this head’s best feature is the price. Since it is still built on a GM assembly line, you can purchase a complete pair of these heads from a GM Performance Parts dealer for well under $500.
The head does have limitations. The valve springs won’t accept more than 0.470-inch lift and the guide boss is very large, which limits some springs. Comp now makes a beehive spring that will work, but you should machine the guide boss down for more retainer-to-seal clearance. Or, you can purchase a modified set of these heads from Scoggin- Dickey or one of several other GM Performance Parts dealers that offer modified heads. The Vortec has a 64cc chamber and requires the use of a center bolt valve cover as well. Perhaps its biggest drawback is its unique 8-bolt intake manifold bolt pattern that requires Vortec-specific manifolds. In comparison with other GM iron small block heads, the Vortec is superior to them all, including the cast iron Bow Tie head, which means there’s no reason to run the Bow Tie unless the rules dictate its use.
World Products’ Sportsman II head still enjoys some popularity, which is the result of its position as one of the earliest aftermarket performance iron heads. Unfortunately, it’s past its prime and not really up to today’s cotemporary flow standards, despite its 200cc intake port volume. Ironically, a properly set up Vortec head would probably out-power the Sportsman II and do it for less money. World Products also offers a relatively new 220cc Motown iron head that appears to be a decent flowing head with good power potential. This head is offered only with a 64cc chamber, 2.055/1.60-inch valves, and either angle plug or straight plug configurations. As with most cylinder head companies, you can purchase these heads either bare and equip them with your own valves and springs, or purchase them complete. There are also two spring options, either 1.437-inch or 1.550-inch duals, with the larger spring offering more spring pressure.
The newest cylinder head company is a New Zealand operation called Pro Top Line. Pro Top Line offers a staggering array of different small-block cylinder heads, including some wild 14-degree valve angle castings intended for circle track racing classes that dictate the use of an iron cylinder head. Among the more streetable iron stuff is a line of heads called the Pro Lightning heads featuring 180, 200, 220, 228, 235, and even some large by huge 243cc intake port volume designs. Most the heads come with either 64 or 72cc chambers. The 180 to 220cc heads are relatively affordable priced between $900 and $1000 per set with good springs and stainless valves. These are virtual clones of Top Line’s aluminum Pro Lightning heads that we’ll get into in more detail in the aluminum head section.
Dart also offers an excellent lineup of Iron Eagle castings ranging from 165, 180, 200, 215, and even 230cc intake port volumes. Like the Top Line heads, Darts’ iron heads are very close cousins to the Pro 1 series of aluminum heads, but with a wider selection of port volumes. The Dart iron heads that look the most appealing are the 200 and 220cc intake port versions that offer the best potential for a big-inch street engine based on their flow potential. The largest 235cc head could also be good for larger engines displacing more than 420ci. These heads are less expensive than Dart’s aluminum versions, but have the potential to flow just as much air.
The downside to any iron head is of course the weight penalty. In addition, iron is more time-consuming to modify and is much more difficult to repair should one crack or be damaged. This also means iron heads will cost more to repair compared to aluminum. Generally speaking, assembled Dart iron heads save around $200 per pair, depending upon which head you choose. With an overall cost of roughly $1,100 for a pair of assembled aluminum heads, it appears the aluminum castings would be the smarter buy, if only for the weight savings.
This leads us directly to the filletmignon of this chapter, which is the aluminum castings. Since there are so many heads on the market, we’ll focus on only the most popular and best flowing heads for the street. We’ll remain with 23- degree heads since they offer the best performance for their cost.
Air Flow Research
Both alphabetically and from a pure performance standpoint, Air Flow Research (AFR) heads are among the best performing street heads on the market today. Among the street heads that would fill the bill for a big small block include the 180, 190, 195, 200, 210, 220, and 227cc heads in the standard 23- degree valve angle, standard-port configuration. There’s also a 215cc Raised Runner head that retains the 23-degree valve angle but raises the entry point of the intake port to straighten the runner for superior port flow.
The newest of the AFR head family is the 180cc head which has excellent flow for its rather small port size and is rumored to actually out-flow its older but well-established 190/195cc cousins. This head would be perfect for a big torque application on a 383 or 406ci small block aimed at a truck or towing application. The larger 190/195cc heads are grouped together here since they are identical except for the port entry size. The smaller 190 is designed to be used with smaller intake manifold applications like an Edelbrock Performer while the 195cc head employs a larger port entry that is intended for use with larger, single-plane intakes like the Victor Jr. or Super Victor style manifolds.
The 210 and 220cc port heads would be best used with a larger displacement small-block such as a 420, 427, 434, or 454ci small block, since the larger intake port would be able to feed these larger displacements. Flow numbers on the 220cc AFR head are on the order of over 280 cfm at 0.600-inch lift while maintaining excellent flow numbers even at the mid-lift positions. Of course, the exhaust side is also important, and all the AFR heads match an excellent exhaust port with the intakes, which create a great opportunity to make power.
The only reason you wouldn’t seriously consider the AFR heads would be because of budget constraints. The AFR heads consistently deliver outstanding performance and torque for excellent street power. As an example, we have tested a 383ci small-block with 9.5:1 compression using a set of 190cc AFR heads, a set of 1 3/4-inch headers, a dualplane intake, and a Comp Cams hydraulic roller camshaft (236/242 degrees of duration @ 0.050-ich tappet lift with 0.520/0.540-inch valve lift). This particular 383 made 517 ft-lb of torque and 503 hp at 6000 rpm. This engine also made well over 450 ft-lb of torque at 2500 rpm.
This Mena, Arkansas, facility created by J.V. Brotherton started out building exotic aluminum heads for circle track racing. Over time, Brodix has created what might just be the widest selection of small-block Chevy aluminum castings of any manufacturer. Brodix has recently fired up its small-block cylinder head machine with a series of new heads. The newest is the Fast Burn 1000 series of 23-degree heads that features a 196cc intake port with 2.02, 2.05, and 2.08- inch intake valve options, each with a 1.60-inch exhaust. The heads offer a dual intake bolt pattern to handle either the standard or Vortec intake manifolds. They also use the standard exhaust port configuration. This casting will also accommodate either the perimeter style or center bolt valve cover arrangements. With such a new head, there is no “book” on this head as yet, but it looks promising with flow numbers in the 240cfm range at 0.500-inch lift.
Brodix has also redesigned the original Track 1 head using a 221cc intake port volume with 2.08/1.60-inch stainless steel valves and a 67cc combustion chamber. As with all the Brodix heads, there are CNC options available, as well as selections for valve springs, and other optional valvetrain equipment. Brodix claims the new Track 1 will flow over 260cfm at 0.500-inch intake valve lift. Also, the Track 1 utilizes an exhaust port that can create around 70 percent exhaust to intake flow ratio at 0.500-inch valve lift. In addition, Brodix also has built a series of 23-degree small-block heads that include the -8 Pro (185cc), -8 STD (194cc), -10 STD (210cc), and -11 STD (221cc) plus a -11X that pushes port volume to 225cc. These heads all come fully assembled with straight or angled plug options and excellent flow potential.
One of Brodix’s strengths is that virtually any head is available in very specific configurations. It’s possible to obtain a head prepared anywhere from a pure, as-cast, ready to assemble state, all the way up to fully CNC-machined with prepped chambers, hand-blended valve bowls, or in any combination you wish. All you have to do is tell them what you want and they’ll build it for you.
This is Pro Stock master Richard Maskin’s Detroit-based company that has slowly created a solid reputation in the industry for high-quality products that perform as advertised. Dart’s Pro 1 series of aluminum heads are the streetoriented castings that combine excellent intake and exhaust port designs to create some of the best small-block heads in the business. The lineup includes 200, 215, and 230cc intake port heads in the standard 23-degree valve angle. In addition to the as-cast heads, Dart also offers a fully CNC-ported version of the 215cc head the ends up with a 227cc intake port and an 85cc exhaust port. This head promises serious flow of over 300 cfm and would be an outstanding head on a large cubic inch small block like a 434 or 454ci mouse motor. This particular head sells for over $2,300 per pair complete. But considering that it offers such incredible airflow for a 23-degree head, while accepting all standard 23-degree valvetrain components, it is hard to ignore. All these Dart heads are available with either 64 or 72cc chambers and also offer the options of 1.437- or 1.550-inch diameter valvesprings to be compatible with hydraulic or mechanical roller camshafts. Dart also offers a line of both single-plane and dual-plane intakes to go along with this selection of heads.
Edelbrock offers a relatively wide range of heads that spans the entire range of applications from conservative small-block Performer and Performer RPM heads to fully ported High-Port CNC Chapman heads that deliver seriousflow for a more competition-oriented small block. The Performer RPM head makes for great, torque-enhancing cylinder head for 383ci street engines with its 170cc intake port. Next up the ladder is the Edelbrock Victor Jr. 23 degree head that increases the intake port volume to 215cc with CNC-ported entries and 0.400-inch raised exhaust ports. The heads come with 2.08/1.60- inch valves and a 70cc chamber. Edelbrock offers this head with several different valvespring applications, or you can purchase the head bare. There’s even an as-cast head ready for professional porting. This head still works with 23-degree valvetrain pieces and intake manifolds.
Another excellent head that Edelbrock offers is the new E-Tec 200cc head. The larger intake port generates an excellent intake port flow that peaks around 280 cfm and can still generate excellent flow numbers at 0.300 and 0.400-inch valve lift on the intake side. The exhaust port is no slouch either. This head certainly has 500 hp-plus capability and would be an excellent choice on a mid-sized small block around the 383 or 406ci.
The largest Edelbrock head series includes the Edelbrock/Chapman Victor 23 degree High-Port CNC heads. These heads come in port volumes of 238cc, 243cc, and up to a monstrous 247cc volume. These heads require custom offset rocker arms because of the 0.350-inch intake offset and zero offset on the exhaust side. This high-port design also necessitates 0.200 or 0.300- inch longer 2.100/1.625-inch valves to accommodate the ports. The smaller 238and 243cc heads could be used on a large displacement engine of 420ci or larger. These tend to be on the exotic side of the street cylinder head market, but could be considered if for no other reason than the fact that large displacement small blocks were also considered exotic no more than a few years ago.
Trick Flow Specialties (TFS) is a Summit Racing-owned company that began by specializing in small-block Ford heads. They have also branched out with several excellent small-block Chevy castings that produce great results for the money. The basic 23- degree TFS head is actually a superb medium-port, 195cc small-block head employing standard 23-degree valvetrain pieces and 2.02/1.60-inch valves. The exhaust port generates a good 70 to 80 percent exhaust-to-intake relationship with a standard 64cc chamber size. TFS does offer a CNC-machined 72cc chamber, but that comes at an additional cost. Flow numbers on this head are excellent, which makes it easy to create 415 hp from a basic 350, offering the advantages of excellent torque from a 383 or even a 406ci small-block. This should be enough to support a solid 450 to 475 hp with around 520 ft-lb of torque with excellent power just off idle.
If this is a little too small for your liking, TFS also offers an outstanding 215cc intake port 23-degree head that offers an aggressive intake port that is worth some serious power, especially with a larger inch engine like a 420-434ci mouse. The heads run a 67cc chamber fitted with 2.08/1.60-inch stainless steel valves. You also have the option of heads with either 1.520 or 1.550-inch diameter valvesprings, depending upon the cam you intend to run. The valve seats are ductile iron with bronze guides and beefy ten-degree retainers and locks.
The Motown 220 Lite is World’s entry into the larger port small-block head market. This head features 2.055/1.600-inch stainless steel valves enclosed in a 64cc chamber. The head will accept all the normal 23-degree small block valvetrain pieces. The Motown 220 Lite assembled head uses Manley Race Master stainless steel valves, PC seals, and Manley 10-degree retainers and keepers encompassing either 1.440 or 1.550-inch springs. Airflow numbers for these heads are not quite up to the point of other heads of the same port volume, but they are affordable both in bare or complete form. The combustion chambers are completely CNC machined, which is the major difference between the iron and aluminum versions of this head.
Written by Graham Hansen and Posted with Permission of CarTechBooks