As the economy continues to come out of its slump, cylinder head manufacturers are seeing a growing demand for new cylinder heads that can deliver race-winning performance.
Whether the heads are upgraded aftermarket heads for traditional small block/big block Chevy and Ford applications, or hot heads for the latest generation of Chevy LS and Ford modular engines, people want the latest heads that make the most power.
Heads do make horsepower, but they don’t make it all by themselves. A set of killer aftermarket performance heads that are mismatched with a camshaft, valve train or induction system will never realize the engine’s full potential. It’s all about achieving optimum airflow and velocity within the rpm range where the engine is built to produce power.
That’s where many a racer has gone astray. They overbuild a street engine with race components that are designed to deliver high rpm power instead of building the engine to produce more low-end and mid-range torque. Even in all-out racing the engine with the biggest heads and biggest flow numbers doesn’t always win the race.
Is Bigger Really Better?
A lot of people are true believers in the “bigger is better” philosophy when it comes to selecting cylinder heads. Head manufacturers as well as those who port heads make a big deal out of promoting the huge cubic feet per minute (cfm) flow numbers they’re able to achieve using the wizardry of flow bench testing and CNC machining. Flow numbers are up, but the numbers can sometimes be misleading because of the way the numbers are measured.
Airflow depends on valve lift, valve area, air density and the test pressure. There are industry standard methods for calibrating flow benches and correcting airflow numbers to compensate for differences in air density. However, airflow values can vary somewhat from one flow bench to another depending on the methodology and equipment that are used to measure it. Most flow benches have a margin of error of around plus or minus one percent. On a cylinder head that flows 400 cfm, the margin of error could be plus or minus 4 cfm either way.
Because of this, comparing the airflow numbers claimed by one head manufacturer against those of another may not be the most accurate way of comparing performance. The only accurate way to compare one head against another is to test them on the same flow bench under the same conditions. Even then the airflow numbers won’t necessarily give you an accurate picture of which head will actually produce the most power on a given engine application.
It’s also important to note the valve lift at which advertised airflow numbers are calculated. How do their numbers compare to the actual amount of valve lift the cam and rocker arms in your engine will achieve? Big flow numbers at 1.00? of lift are meaningless if your cam and rockers only open the valves .850? or less. And on a street application, most engines won’t see much more than about .550? to .600? of lift.
Another point to keep in mind when comparing airflow numbers is that the valves reach maximum lift only once during the intake and exhaust strokes. Flow numbers at peak valve lift may be impressive, but what’s usually more important is how well the head flows at partial valve lift as the valves are opening and closing (which happens twice during every intake and exhaust stroke). Better flow characteristics at partial valve lift can have more of an effect on power and torque than big airflow numbers at peak lift.
Accurate cylinder head comparisons mean you should look at the entire flow curve from low lift to maximum lift. Once you’ve done that, you will have a much better picture of how the head will actually perform on the motor you are building.
Also, there’s more to airflow than big cfm numbers. Air velocity and swirl are also important. A port that’s sized properly for the engine displacement and rpm range will keep the air moving at higher velocity, resulting in more complete cylinder filling and more power. Air velocity affects both throttle response and low-end torque. That’s why heads with port runner volumes that are too large for a given engine application may not perform as well as a stock cylinder head.
Swirl helps route air into the cylinder more efficiently and promotes better air and fuel mixing for better combustion. Swirl and turbulence can also cause air and fuel separation in the combustion chamber, which is something that can be visualized by wet flow testing.
Valve angle (the angle of the valve stem with respect to the deck surface) also affects airflow, and here shallower is usually better. The configuration of the combustion chamber, valve shrouding and even the diameter of the cylinder bore are additional factors that also affect airflow and a head’s ability to make power.
The best way to compare cylinder heads is to bolt them on an engine and do a series of dyno test runs to see how they perform. The best head is not necessarily the one that makes the most peak horsepower in a narrow rpm range, but the one that delivers the best power and torque curves for the intended application. If you’re building a motor for a drag car, then peak high rpm power is what you want. If the engine is going into a circle track car, you want good throttle response and peak power in the mid to high rpm range. For a street application, a broad flat torque curve and lots of low and mid-range torque works best.
As Cast Or CNC?
There’s an ongoing debate as to whether or not ports in an “as cast” cylinder head flow as well as those in a CNC machined head. Many aftermarket performance cylinder heads that are sold with “as cast” ports are capable of delivering excellent performance out of the box with no additional modifications. The same goes for some stock heads (such as Chevy LS1 heads) that flow very well in their stock configuration. But there’s always room for improvement by either hand porting or CNC machining “as cast” heads to change the contours of their ports, bowls and combustion chambers for better flow. It depends on what you are trying to achieve.
Most CNC profiles are developed by grinding, testing and mapping various port configurations for a particular application. People who do this kind of work build up a digital library of port configurations that work well with various head castings, camshaft and engine combinations. This allows them to replicate a proven port configuration by entering the data into a CNC machine and removing the unwanted metal to modify the cylinder head.
Is the end result better than the best “as cast” head for a given engine application? It depends on the castings that are available and how well they flow compared to an optimized CNC port configuration for the same setup. With most high-end performance heads, a raw casting is CNC machined to specific dimensions for that application to deliver peak performance.
Bigger is better continues as the trend among Pro Stock drag racers. The 600 cubic inch “monster motors” of a few years ago seem almost puny next to the 850 and 900 cubic inch motors that are now commonplace on the drag strip. Sonny’s Racing now has a 1,000 cubic inch naturally aspirated motor that makes over 2,150 horsepower and 1,550 lbs. of torque. It’s hard to tell how far this trend will push engine displacements in the years ahead.
The bigger these motors get, the more air the cylinder heads have to flow to handle the added cubic inches. The availability of aftermarket engine blocks with wider bore spacing continues to expand, and with it the availability of larger cylinder heads from Brodix, Dart, Alan Johnson Performance Racing (AJPE) and others to fit these engines.
Another trend we’ve seen is that of reducing valve stem angles and raising the ports for increased airflow. This, in turn, often requires custom fabricated intake manifolds or special intake manifold castings to mate with the modified heads (ala Brodix, Dart, etc.). With these types of heads, installation is not a simple swap. Changing the head may also require changing the intake and exhaust manifolds, and possibly even the valve train configuration.
For small block Chevy applications, splayed valve symmetrical heads such as the Brodix BD Series heads are now available to replace siamese-style SBC heads. The symmetrical heads seal better and reduce the risk of head gasket failure in the hot spot area between adjacent exhaust valves on siamese style heads. The ports also provide a straighter shot at the valves than the ports on siamese heads.
To find out what the latest cylinder head offerings are and what’s being done with some of these heads, we contacted various aftermarket head suppliers and engine builders for their input. Here’s what they said:
Tony Mamo of Air Flow Research said AFR has recently redesigned their entire line of small block Ford cylinder heads. “Our new Renegade line provides about a 20 cfm improvement over our previous Outlaw series of small block Ford cylinder heads. For example, our 185cc street head used to flow 270 cfm but now flows 300 cfm. That’s a gain of over 11 percent!”
Other new heads from AFR include a 15 degree small block Chevy CNC racing head that flows over 400 cfm with 285 to 305 cc port runners. Also new is a 13-1/2 degree SBC Chevy CNC racing head with taller intake ports that flows over 450 cfm. This head does require a custom fabricated intake manifold. Mamo said that eventually they will offer a matching cast manifold that will work with this head.
“We’re getting back into the high-end racing market with these heads and some other future projects we’re now working on,” said Mamo. “In the next 12 to 24 months, we will also have a square port Chevy LS6 head to add to our current line of cathedral port LS heads.”
A new line of “Head Hunter” series 23 degree SBC Chevy heads from Brodix features .400? raised oval intake ports with 225 or 234 cc intake runners. Jason Neugent of Brodix says the 225 heads flow over 335 cfm while the 234 heads deliver over 345 cfm. The heads do require offset rockers and use a steeper 52 degree angle on the intake valve seats and 55 degree angle on the exhaust seats with 2.150? diameter intake valves and 1.570? exhaust valves.
“The small block Chevy market has been good, and we’re seeing more demand for heads to fit blocks with 4.500? bore spacing that allow displacements of up to 500 cubic inches. We have some 13 degree siamese heads for these that flow over 380 cfm, and a symmetrical head that flows over 400 cfm.
“We’re also seeing more interest in big block Chevy heads for 600 cubic inch and larger motors,” said Neugent. For 496 to 600 cid engines, Brodix’s new BB-3 Xtra Series heads feature a two degree shallower intake valve angle for improved airflow. Available configurations include a choice of oval (332, 351 and 365 cc) or rectangular (366 and 380 cc) ports in “as cast” or fully CNC machined versions. Brodix says the CNC ported 338 cc heads flow over 440 cfm while the “as cast” heads are good for a 30 horsepower increase over standard BBC heads.
Butler Performance specializes in building traditional big block Pontiac engines for both drag race and high-end street performance customers. Dave Butler says he modifies Edelbrock aluminum D-port cylinder heads to match the cam, displacement and application his customers want. The heads fit 1962 to 1979 389, 400, 421, 428 and 455 V8 engines with 4.060 inch or larger cylinder bores. The same heads can also be used on 350 engines if 1.66 exhaust valves are use and the top of the block bores are chamfered for valve clearance.
Dave says much of his business has been building Pontiac engines for drag racers, but lately he’s doing more high-end street, large displacement pump gas engines. “I’ll get customers who want me to build them a 600 to 750 horsepower street engine for their muscle car. To get there, I’ll CNC machine the Edelbrock heads with a port profile that best matches their requirements.” Dave said he develops his port profiles on his flow bench, and then hand ports or CNC machines the heads as required. “The Edelbrock D-port head flows 260 to 270 cfm out of the box. After reworking the head, we can make it flow 330 to 340 cfm, which is what it takes to reach these kind of horsepower numbers,” says Butler.
Butler says he’s also building some LS engines for late model Pontiacs using a variety of aftermarket cylinder heads from AFR, Edelbrock and RHS. “We haven’t done any custom head work on the LS engines yet as we’re still building engines and learning what works best. But eventually we will probably be reworking LS heads too.”
Bud Keating says “Our market continues to be small block and big block Chevy cast iron and aluminum heads, and small block Ford cast iron and aluminum heads. We don’t have any new heads for Chevy LS or Ford modular engines. Our main market is primarily cast iron performance heads for street, circle track and drag racing Chevy and Ford engines.”
Keating said Dart heads are available in “as cast” or CNC ported versions, and billet aluminum heads are available for drag racing. “The demand for cast iron heads is strong because some race sanctioning bodies don’t allow aluminum heads. Our cast iron heads provide an affordable performance improvement over stock cast iron heads, and are stronger than the stock castings.”
Eric Blakely of Edelbrock says his company now has more cylinder head applications for NHRA Stock/Super Stock small block Chevy LSX style LS-R canted valve heads, big block Chevy race heads, and Big Victor 12 degree, 14-degree and Big Victor III heads. For circle track, there are new SB2 & ROX heads, and Pro-Port Raw cylinder heads for both drag racing and circle track.
Edelbrock’s new “E-Street” line is an affordable entry-level cylinder head for street motors with cam lifts up to .500?. There is also an “E-CNC” line that is fully CNC ported for high performance street applications and entry-level race applications.
Some product improvements in various head designs include extra drain back holes, thicker walls for custom machining and/or porting, raised valve cover rails for added valve train clearance, relocating valves to fit the cylinder bores better and to reduce shrouding, and a special HIP casting process that reduces porosity and improves strength.
Goodwin Competition Racing Engines
Todd Goodwin’s performance engine shop is a full service facility with two engine dynos, a chassis dyno and CNC machining capabilities for doing raw castings and even custom pistons. Goodwin says most of his business is building engines for high end drag racing, truck pulls, off-road truck and also late model Mustangs, Camaros and other performance cars. “We work with all brands of aftermarket heads and can also do custom billet aluminum heads if that’s what a customer wants.”
When it comes to choosing or reworking cylinder heads, Goodwin says airflow numbers are only one piece of the puzzle. “You also have to look at port cross-sections, volumes, air velocity, valve sizes, the intake manifold, the design of the combustion chamber and even the tops of the pistons. It’s all about matching everything to get the right combination that delivers the kind of performance a customer wants. If we’re designing the ports and combustion chamber for a head, we also like to do the pistons because they are part of the combustion chamber, too.”
Chad Bowling says Patriot introduced their new Predator Head for Chevy LS engines about a year ago that features raised valve cover rails for extra rocker arm clearance. The head flows 303 cfm on the intakes at .600? lift, which is about 70 cfm better than the stock LS head. “This head will bolt up to the stock manifold but does require measuring and changing the pushrods.
“Our Freedom SBC 185 and 190 cc street performance heads are still our most popular products. The line includes cast and CNC ported versions with 195 to 225 cc intake runners for street and racing applications,” says Bowling.
The newest offerings from Pro-Filer Performance Products include a new 13 degree All American series head for small block Chevys in cast or CNC machined versions, a new splayed valve symmetrical port head with cast ports for small block Chevy engines, and a new Ford 460 canted valve cast aluminum head with oval Pro Stock style intake ports that flow over 520 cfm.
Michael Green of Pro-Filer says the shallower valve angle on the new 13 degree All American Chevy heads combined with the 300 cc fully CNC machined ports flows over 400 cfm. The heads also have a solid rocker bar for better valve train control.
According to Kevin Feeney of RHS, the new Pro Elite LS7 rectangular port aluminum head is a clean sheet of paper design. “These heads are compatible with RHS LS race blocks and GM LSX blocks. The heads are CNC machined and have a shaft style rocker system that can mount standard GM LS7 rockers, which allows the valves to be adjusted. The heads have a 12-degree valve angle, with intake ports that have been raised .220?. But you can still bolt the heads up to a stock intake manifold. The exhaust ports are also raised .100? to improve flow. As a result of these changes, the new LS7 heads are good for a 35 horsepower improvement over the stock heads,” says Feeney.
Steve Schmidt Racing
At the recent Race EXPO show in St. Charles, IL, Steve Schmidt Racing unveiled a high unusual and unique two-piece hemi cylinder head for big block 18-bolt Chevy and Ford engines. The combustion chamber portion of the head is identical for both applications but the top half of the head can be swapped to make it fit a Chevy or Ford engine. The two halves are sealed together with copper o-rings.
“We’re currently running this head on a 648 cubic inch truck pull motor, but we also see a market for this head for Competition Eliminator, Top Sportsman and Top Eliminator drag race classes,” said Jeff Sams of Steve Schmidt Racing. “The intake ports can flow 640 cfm at 1.100? valve lift, which means this head is capable of making about 2.8 horsepower per cubic inch on a naturally aspirated engine. The head is machined from billet aluminum, and is available with or without water jackets. “The price: a mere $16,000 (yes, thousand!) per pair. Though expensive, the cost is still much less than high-end heads from some professional racing head suppliers.
Trick Flow’s newest product is their Twisted Wedge Race 195 cylinder head for modular Ford engines. The heads are fully CNC machines, and are available as bare or fully assembled heads.
“This head has been optimized for engines with 3.700? bores, not stock bores,” says Mike Downs. “The head likes lots of cam lift and also works well with a turbocharger or blower on the motor. On an otherwise stock 322 cid engine, these heads have made 520 horsepower with the stock manifolds.
“We are also finishing up work on a rectangular port head for Chevy LS applications that should be production ready by the 2nd quarter of this year. The LS market is one of the hottest markets today, so this new head will be a good addition to our cathedral port LS heads that we have now.” says Downs.
World Products continues to market their stock cast iron cylinder heads under the World brand name, but their performance heads and aluminum heads are now being marketed under the Bill Mitchell Products (BMP) name.
“We don’t have anything that’s brand new,” says Bill Mitchell, “But we have a broad selection of heads for small block and big block Chevy, Chevy LS and small block Ford engines. Products include their Mowtown cast iron and aluminum SBC heads, Merlin oval and rectangular cast iron and aluminum BBC heads, Warhawk 15 degree LS1, LS2 & LS6 aluminum heads, Warhawk 12 degree LS7 heads, Windsor Jr. an Sr. FSB cast iron heads and Man O’War 10 and 18 degree SBF aluminum heads.
What’s Mitchell’s advice for choosing cylinder heads? “Ignore all the BS about flow numbers. Heads that have great flow numbers don’t always run that great. We have heads that can make 1,000 horsepower on a 565 cid big block motor, but do you really need that much power on the street? You really have to match the head to the application and build the engine around the head and camshaft combination.”
For a complete list of performance cylinder head suppliers, visit our online High Performance Buyers Guide.