Choosing a cylinder head for your small-block can be a challenging task because of the shear number of heads available. Since the mid- 1980s and the introduction of factory designed Bow Tie heads, Pontiacdesigned small-block heads, and numerous performance aftermarket heads, picking the right head has become more or less a matter of choosing the best casting for your specific application. While earlier editions of this book defined and illustrated the original Chevy performance head castings, they are becoming difficult to locate. Engine builders are now turning to currently available factory heads or aftermarket replacement heads that incorporate the improvements Chevrolet and engine builders have discovered over the years. If you don’t already have a good set of original castings and you don’t absolutely need them for restoration purposes, aftermarket or Bow Tie factory heads are a much better choice. We’ll begin by examining currently available factory cylinder heads and then describe many of the aftermarket heads in detail.
This Tech Tip is From the Full Book “SMALL-BLOCK CHEVY PERFORMANCE: 1955-1996“. For a comprehensive guide on this entire subject you can visit this link:
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HO Aluminum Head
The current factory HO aluminum head PN 12556463 is very affordable and it comes completely assembled and ready to run. It includes valves, springs, retainers, 3⁄8- inch screw-in rocker studs, and guideplates. This cylinder head is used on high-performance HO engine assemblies, and it is based on the Corvette light alloy castings PN 10088113. It comes with heavy-duty valvesprings, PN 12551483. It also incorporates advanced design features such as Dshaped exhaust ports, high-velocity intake runners, and centrally located spark plugs for improved combustion efficiency. The combustion chambers measure 58 cc and valve sizes are 1.94 inch and 1.5 inch for the intake and exhaust. You should also be aware that this head has raised rocker cover rails with machined surfaces, so early style four-bolt rocker covers will not fit. Best of all, a pair of these heads will eliminate almost 50 pounds of dead weight from the front of your car.
If you decide to use this cylinder head, you may need to make some additional modifications. Because the exhaust ports exit approximately 0.100 inch higher than the stock, headers and exhaust manifolds may require some minor modifications. In addition, make sure there is adequate clearance around the angled park plugs. AC FR5LS 3⁄4-inch reach spark plugs with 5⁄8-inch hex heads are recommended, and late-model rail type rocker arms are required (PN 10089648). These heads aremachined on both ends to accept standard accessory mounts, and they should be installed with composition head gaskets having stainless steel fire rings to prevent a galvanic reaction (a form of corrosion) between the aluminum head and cast-iron block.
Cast-Iron Performance Heads
You have four basic choices if you prefer to use a cast-iron head. The first was originally used on the factory 285- hp350-ci engines (PN12353641).Available under PN 10125377, this head has the 1987 and later intakemanifold bolt pattern having a 72-degree angle on the two center bolts. It uses 1.94-inch/1.5- inch diameter valves, 64-cc chambers, and PN 3901068 valvesprings.
Your second choice is the service head PN 12356026 used on the 300- hp 350SP engine (PN 12355345). It also uses 1.94-inch/1.5-inch diameter valves, 64-cc chambers, and requires late model, center-bolt valve covers. The primary difference between this and other cast-iron heads is that this head uses the standard pre-1987 bolt angle on the intake manifold’s center bolts.
A large valve, high-performance head is offered under PN 12480092 . This head was used on the 1960 Corvette 283, as well as later Z28 302s and 350-ci LT1 V-8s. It features 2.02-inch/1.6-inch diameter valves and 64-cc chambers. A large chamber version is available under PN 464045. It was designed for low compression small-blocks, and its large 76-cc chambers are perfect for today’s low-octane environment. It delivers 9:1 compression with the flat-top pistons used in LT1, Z28, and L82 (1971–1979) engines. The head has 2.02-inch/1.6-inch valves, heat-riser passages, screw-in studs, and pushrod guide-plates. The valve seats are heat treated for use with unleaded gasoline, and the straight spark plugs will clear all manifolds and most headers.
Bow Tie Racing Heads
Phase 2 Cast-Iron Bow Tie Head
The Phase 2, Cast-Iron Bow Tie head, PN 12480053, is Chevrolet’s top-of-the-line cast-iron cylinder head. This casting was designed for competition use in applications where aluminum heads are prohibited. This head offers several advantages over the Phase 1 head it replaces. The exhaust heat risers are deleted, and hardened exhaust valve seats are included. Phase 1 and Phase 2 Bow Tie heads are easily distinguished from one another. While Phase 1 heads have a thin raised parting line between the exhaust manifold flanges, Phase 2 heads have a much wider machined bar, and the water temperature sensor pad is also machined flat.
Phase 2 heads have 64-cc combustion chambers and the quench area beneath the spark plugs is filled to provide increased compression in competition engines. All Phase 2 heads have 2.02-inch/1.6-inch diameter valves with hardened seats for the exhaust valves. Phase 2 heads have the same ports as the earlier Phase 1 heads, including the 190-cc intake ports. They are the highest-flowing cast-iron production heads currently available from Chevrolet. The valvespring pockets will accept 1.5- inch diameter springs. Phase 2 heads are machined and tapped for screw-in studs (PN 3973416 for 3⁄8-inch studs or PN 3921912 for 7⁄16-inch studs) and guideplates (PN 3973418), which must be purchased separately. Phase 2 heads require 5⁄8-inch hex-head spark plugs with tapered seats and a 3⁄8-inch reach.
Raised-Runner Aluminum Bow Tie Head
Raised-runner aluminum Bow Tie heads, PN 10051101, have intake runners that are 0.200-inch higher than the stock small-block port location to improve the line-of-sight delivery to the valves. These feature 0.240-inch minimum port wall thickness to suit all porting requirements. Deck surfaces are 0.600-inch thick, and the 55- cc combustion chambers are designed to increase compression without promoting detonation. The rocker covers are raised 0.300 inch and the intake manifold flange is stepped for improved gasket sealing. Use 3⁄4-inchreach plugs with either gaskets or tapered seats. Raised runner heads do not have pushrod clearance holes, so the pushrods can be positioned with optimum porting in mind. Valveguides and seats are not included, and you must purchase the separate guideplates PN 14011051. Longer than stock (0.100-inch) aftermarket valves are required, but stock length valves can be used if you remachine the spring pockets. A special raised- runner, single 4-barrel intake manifold (PN 10051103) is recommended.
18-Degree High-Port Aluminum Bow Tie Heads
These high-port 18-degree heads (10134364) have all the same performance features as the low-port version, but the intake runner floors are raised 1.220 inch above the deck surface. PN 10134363 is designed for fuel-injected applications with larger bore sizes of 4.060 to 4.125 inch. Smaller bore engines from4.00to4.060inchshould use the alternate 18-degree head (PN 10134364),which has ideal valve positions for smaller bores. The former NASCAR Winston Cup version of the 18-degree head is offered under PN 24502482. It’s identical to PN 10134364 except that the ports are CNC machined and the valveguides and seats are included.
Pontiac Motorsports Aluminum Head
This cylinder head (PN 10033867) was originally developed by Pontiac Motorsports and offers strong performance potential while retaining the standard intake port location. It comes with ductile iron valve seats installed for standard length 2.100-inch intake valves and 1.625-inch exhaust valves. Phosphorus bronze guides are included, but not installed, as a convenience for the head porter. These heads have 62-cc combustion chambers and use 3⁄4-inch reach, gasketed, 14-mm spark plugs.
Aftermarket Performance Heads
Some of the best horsepower-perbuck values are found in the current offering of aftermarket performance cylinder heads.With only a fewexceptions, they are aluminum alloy and have been carefully developed tomeet the broad range of specialized requirements found in modern small-block engine applications. Leaders in the aftermarket cylinder head market include Airflow Research, Brodix, Dart Machinery, Edelbrock, Trick Flow, and World Products. Some, like Airflow Research, Brodix, and Dart also offer top echelon heads for all-out racing, as well as performance street heads. For specifics about these racing castings you’ll want to contact the manufacturer for their latest offerings.
Airflow Research Heads
Airflow Research has been a long respected name in the cylinder head business, and they hold the distinction of being the first company to win a California exemption number for their late-model aluminum street head. Available with either 180- or 195-cc intake runners, and 68-cc closed chambers or 74-cc open chambers, these heads use 2.02-inch-diameter intake valves and 1.60-inch exhaust valves, hardened seats, and 0.750-inch-thick deck surfaces for reliable street performance. They are available in several configurations, including a standard street design with 74-cc chambers, as well as various smog-legal versions. AFR also offers raised-port and racing heads with 210-, 215-, and 220-cc intake runners, plus a variety of specialapplication racing heads built to suit specific customer needs. They also revisit their designs periodically to make sure they stay current with the latest advances.
Brodix Aluminum Heads
Beginning at the top of the order (just below their all-out racing heads), the Brodix Track 1 is a top-line street/race aluminum head with 221- cc intake runners, 67-cc combustion chambers, 2.08-inch intake valves, 1.60-inch exhaust valves, blended valve bowls, a three-angle competition valve job, roller rockers, screw-in studs, guide-plates, springs, retainers, and 10- degree locks. Spark plugs are angled and the exhaust ports require headers with 15⁄8-inch or larger primary tubes.
If your engine size or application dictates a smaller intake-runner volume, the Brodix Race-Rite series fits the bill. These heads are available with 180- or 200-cc intake runners, 67-cc chambers, and 2.02-/1.60-inch intake/exhaust valves in a quality street/race casting.
Dart Machinery Heads
Dart Machinery offers a variety of different cylinder heads from iron street heads to full-blown aluminum race heads. Since we’re focusing on street heads, let’s take a look at the Dart’s Iron Eagle heads. These cast-iron heads are available with 165-, 180-, 200-, or 215-cc intake ports. You can also choose between straight or angled plugs and 64- or 72-cc combustion chambers. While the 165-cc head has 1.94/1.50-inch valves, the 180-cc and larger heads come with 2.02/1.60 or larger heads, depending on the model. These heads are great for a stealthy look, or in classes where iron heads are required.
If you have your mind made up on aluminum, Dart’s Pro 1 heads will fit the bill. These 180-, 200-, 215-cc or larger heads offer great performance out of the box. You’ll have to choose between 64- or 72-cc combustion chambers, and angled or straight plugs. Valve sizes range between 2.02/1.60- and 2.08/1.60-inch, depending on the model. Dart also offers a number of racing heads with even wilder specs.
Edelbrock Aluminum Heads
Edelbrock’s Performer aluminum heads are designed to complement their intake manifolds and camshafts to provide a total performance package. Edelbrock Performer heads are designed for street operationwith 165- to 170-cc intake runners, 2.02-/1.60- inch valves, and 60-, 64-, 70-cc combustion chambers. The Performer RPM heads have 170-cc runners, 64- or 70- cc chambers, 2.02-/1.60-inch valves, and either straight or angled spark plugs. Performer heads are also available for late-model small-blocks with center-bolt valve covers, as well as 1987–1991 Corvettes.
Edelbrock utilizes a multi-million dollar, computer-controlled machining network that constantly measures tooling wear and makes automatic adjustments to their massive machining centers. This advanced system allows Edelbrock to produce hundreds of components with dimensions held to very high preci- sion. The network, one of the most advanced in the industry, should virtually guarantee the quality of all Edelbrock cylinder heads.
Trick Flow Specialties Heads
The Trick Flow Kenny Duttweiler Signature Series 23-degree aluminum head is a bolt-on street performance piece designed for good low-speed torque and top-end power. These heads come completely assembled with 2.02-/1.60- inch valves and accept all stock-type rockers, headers, factory-type intake manifolds, and accessories. Trick Flow also offers 18-degree heads, as well as heads for the LT1.
World Products Heads
Performance enthusiasts looking for reliable and power-producing cast-iron small-block heads can make good use of World Products complete line of Stock Replacement, S/R Torquer, Sportsman II, andMotown castiron heads. Their Stock Replacement iron heads are designed to replace the dwindling supply of 1962-to-present castings with a feature-laden design. Four part numbers cover the full range, with 67- or 76-cc chambers, 1.94-/1.50-inch valves, and all accessory bolt holes. Four additional part numbers cover the same heads with late model 1986-and-later angled intake faces. All heads feature hardened valve seats to prevent recession from unleaded fuel.
S/R Torquer heads are a low-cost, big-valve power builder. They have 170-cc runners, 67- or 76-cc chambers, 2.02-/1.60-inch valves, screw-in studs, and hardened seats for unleaded fuel compatibility. These heads all feature straight spark plugs to eliminate plug wire problems associated with many header designs. You can buy these heads completely assembled or as fully machined bare castings. Small-bore 305 Torquer heads are available for 305-ci and other small-bore engines. These heads allow the use of larger 1.94- inch intake valves with small bores. They come with 171-cc runners, 58- cc chambers, and screw-in studs. Like the S/R Torquer, they are available completely assembled with valves and springs or as fully machined bare castings.
Dart II Sportsman heads have 200-cc runners with heart shaped 64- or 72-cc chambers, 2.02-/1.60- inch valves, angled or straight spark plug bosses, and hardened seats. Like the other World Products heads, they come completely assembled with a three-angle valve job, or can be purchased as fully machined bare castings. World’s Motown and Motown Lite (aluminum) heads are great for big-inch small-blocks, with 220-cc intake ports and 2.08-inch intake valves.
Regardless of which heads you choose, a good valve job is the first requirement, but before this can be accomplished the cylinder head must be properly prepared. Head preparation should include minor porting to eliminate obstructions and smooth port contours. Many recognized cylinder-head shops perform street porting work that can substantially increase engine performance. Most of the new high-performance cylinder heads are already cast and machined for high-performance work, requiring only minor additional touches. If your budget can handle it, and you want a bit more performance, you might consider having one of the reputable shops work over your heads.
On the other hand, you can do a pretty fair job yourself if you work carefully and exercise restraint. A simple job of matching the ports to the gaskets will help. You can also smooth the radius on the short side of the port floor, where it turns into the combustion chamber. This critical shape has a pronounced effect on flow, so don’t flatten the radius. Just smooth the contours. In addition, between the valve seat and port runner, the entire port necks down in the bowl area just below the valve seat. You can improve flow by removing excess material in this area, but make sure you maintain a slight radius between the valve seat and port bowl. The most important thing to remember here is to not get carried away. Think about what you want to accomplish and don’t do it if you have any doubts. You can do more harm than good if you’re careless.
Race-type porting is simply too specialized for most enthusiasts to handle themselves. It is extremely easy to ruin a set of heads as the result of inexperience and overzealous grinder work. Many publications attempt to illustrate various porting techniques, but the benefits are questionable, since many enthusiasts do not have the experience to precisely reshape the ports. The result can be a set of heads considerably less efficient than the stock castings and totally unmatched to the engine requirements. If serious porting work is what you have in mind, the first thing you should do is take your heads to a reputable cylinder head shop and let them perform the work. This is admittedly expensive, but you benefit from the expertise of someone who has been through it all before. Headwork is never cheap. Another, perhaps better, alternative is to purchase a set of ready-to-run ported heads like those offered by most aftermarket suppliers.
Valveguides and Seats
Small-block Chevy engines require tight valveguide-to-stem clearances in order to provide good oil control and accurate valve seating. There are a number of ways to achieve this, depending on the final application of your cylinder heads. A street engine should have 0.0015- to 0.0025-inch valvestem clearance with stock valves. If the clearance exceeds this amount, the guides will have to be reconditioned. There are several options: valveguides can be sleeved or threaded to accept cast-iron or bronze inserts; the guides can be reamed and used with oversize valvestems; the old guides can be machined out and new cast-iron or bronze guides pressed in place; or existing guides can be knurled to regain proper valve fit.
All of these procedures produce acceptable results, except knurling. This quick-fix method will only last a few hundred miles, after which the valves will be rattling around as bad as if the guides were never knurled at all. So, for all practical purposes your choices boil down to using bronze or cast-iron sleeves or replacement valves and guides. There is little consensus on what guide material works best; some machine shops prefer cast iron, others recommend bronze. However, many experts believe that guide life is directly linked to the type of valve seals used to control guide oiling (along with several other factors, including the types of lifters, pushrods, rocker arms, valvesprings, retainers, and even oil and frequency of oil changes). It’s not so much a job of selecting a specific guide and a specific valve seal; it’s using a combination of guides and seals that are known by your machine shop to provide good results.
If your machine shop doesn’t have any suggestions, consider these combinations recommended by engine expert Jay Steel from Taylor Engines in Whittier, California.
Stock Engines:Use replacement, press-in, cast-iron guides with stock O-ring seals on the valvestems. In addition, use guide-mounted seals on the intake valves only (use black rubber seals with a thin white stem scraper). If possible, also use the stock valvespring-mounted splash shields.
High-Performance:Use castiron or bronze-wall guides with rubber guide mounted seals on both the intake and exhaust valves. Eliminate valvespring mounted splash shields (heavy-duty springs can cut the splash shields in half!) but continue to use the stock O-ring seals on the valvestems, provided the valves are machined for them.
Racing Engines:Eliminate the O-ring seals on the valvestems, particularly when using needle-bearing rocker arms or restricted top-end oil-ing. Unless there is no other choice (e.g., using dual valvesprings), never use all-white Teflon/wire-spring type seals; they restrict guide oiling too much. When you must use Teflon seals, consider using bronze-wall guides, as they seem to survive better with less oil.
After the guides are reconditioned, your machinist can turn his attention to the valve seats. For any application requiring long life on unleaded gasoline, like virtually every street buildup, press-in hard inserts should replace the stock exhaust seats in the cylinder heads. They aren’t inexpensive, but they can add 50,000-plus miles of additional service. Some cylinder heads have induction-hardened seats from the factory and may not require hard-seat inserts; discuss these options with your machinist.
Considering the cost of new valves (about $80 per set), many engine builders opt for new instead of reconditioned valves. Speed-Pro, TRW, and other manufacturers offer valves with hardened tips that can reduce wear with high spring pressures and mechanical (solid-lifter) cams. However, if you’re building a street engine and your valves are in good condition (showing little face, tip, or stem wear), regrinding the faces and stem tips is an acceptable option.
A quality three-angle valve job should always be performed, using a 30-degree top cut, a 45-degree seat, and a 60-degree bottom cut. Seat widths should be about 0.065 inch (to 0.010 inch) for the intake and 0.075 inch (to 0.010-inch) for the exhaust. Seats should be held near the lower tolerance limit for performance use, and widened to near the upper tolerance limit for street longevity. To optimize performance, grind only the minimum amount necessary to clean the seats. The more the valves are sunk into the seats, the less efficiently the ports will flow. If the seats require a lot of grinding, consider installing hardseat inserts in both the intake and exhaust sides or look for replacement head castings.
The final steps in basic head preparation include installing the valvesprings so that they provide the cam manufacturer’s recommended seat pressure. This involves measuring the compressed spring height at which the desired pressure is produced, then adding the appropriate valvespring shims so the recommended pressure is applied to the valve. If guide-type press-on seals are used, the top of the valveguides must be machined so that the outer diameter is concentric with the inner diameter. If this is not done, the seals will not wipe the valvestem uniformly and excess oil may be drawn down the guides, increasing oil consumption and possibly detonation.
Written by John Baechtel and Posted with Permission of CarTechBooks