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HPBG: Choosing Aftermarket Cylinder Heads
With such a wide array of new performance
components on the market, why rebuild stock?
By Brendan Baker
If the performance business is about one thing it’s about improving upon what comes in the door and making it better for your customer’s application, whether he’s racing down the quarter mile, hitting the twists and turns of a natural road course, or just driving it to the movie theater with his girl by his side and a lumpy cam at the lights.
The cylinder head is the heart of the engine, it characterizes the entire engine build. With this in mind, we spoke with several manufacturers to get their take on where the market is now and how to select the right component for your build.
One of the reasons for the shift to new heads vs. old cores is that many cores are no longer available or are in rough condition, and it would take too much time to bring them back to life. In other cases, heads that are designed for OE purposes are not good enough for today’s high horsepower racing applications. Therefore, the aftermarket stepped up to fill this need.
Cylinder head manufacturers have, for the most part, conditioned engine builders and racers to think of the market in three major categories based on performance, durability and cost. The largest category is street or entry level performance. This category is filled with budget-friendly, mild performance cylinder heads that are a step up from OEM. These heads used to be almost exclusively cast iron, but are now mostly aluminum. “Most heads in our budget category come fully assembled to save the customer the hassle of selecting the proper components,” says Mike Downs of Trick Flow. “They’re a bolt on and go deal.”
The next category is the high-end racing heads designed to deliver significant performance increases and are usually assembled by a shop with the highest quality components. “Racing heads are the most expensive category because applications are specialized and many times custom-tailored to suit the needs of a race engine program,” says Downs.
The real growth, according to our experts, has been in “mid-level” heads. You might call them high-performance street or “weekend warrior” competition heads. Engine builders and enthusiasts at this level demand high quality, durability and excellent performance results. They also demand CNC machining it’s practically the price of entry nowadays to this category.
According to Downs, all of Trick Flow’s mid-level heads feature CNC-profiled combustion chambers plus fully CNC “street ported” intake and exhaust runners.
Head manufacturers such as Edelbrock, EngineQuest and others also offer CNC ported heads for street/strip applications. But it depends on the customers’ needs.
“Many of our race head sales start with a conversation between the engine builder and head porter,” says Edelbrock’s Smitty Smith.
Choosing the right cylinder heads for your build is not just about who has the biggest numbers, according to the experts we interviewed. Numbers are important, but so are matched combinations.
Experts say it is important to match the head and intake to your application and intended use (i.e., rpm range). “Cylinder heads are only a small portion of the ‘power equation,’” says EngineQuest’s Eric Haugland. “A good set of cylinder heads on a poor combination will yield virtually nothing but matched with the right combination, it can make a huge difference in horsepower.”
It is a good idea to have a conversation with your customer with questions based on the cubic inch of the engine build and other parameters, according to our experts.
“We typically ask a lot about a prospective customer’s engine,” says Haugland. “Is weight a factor in this build? We also like to know cam type and other components they are running. How many rpms is the customer is looking for is also important to head selection. Port size at this point becomes an issue.”
Since the intake manifold, the exhaust header, and the rocker system all bolt to the head most engine builds use stock geometry heads for simplicity. As the builder moves up in horsepower levels, the stock geometry becomes a severe hindrance to airflow and combustion chamber efficiency.
By raising the intake and exhaust ports up air flow is increased, and the valves can be rotated up creating a more compact combustion chamber. Huge power potential is unlocked, but everything, the piston, the intake and exhaust systems, the valve train is all new.
“At Edelbrock we work with the piston and valve-train companies to ensure compatible product is available, and of course we have the intake manifold solutions,” says Edelbrock’s Smitty Smith.
“We are beginning a new research program at Edelbrock that we call Dynamic Matching,” explains Smith. “Following the same course taken by academic as well as factory research laboratories we can foresee a whole new way of looking at the good old power package. Traditional thoughts about port size, flow velocity, combustion process, and exhaust events are being challenged and in some cases with surprising results.
Contrary to popular belief, Smith says that small, high flowing ports with efficient combustion chambers are always in fashion. “It continues to be the case that trends in racing work their way into the street performance stuff, and we are committed to excellence in both street and now racing as well.”
Experts say that for good throttle response on the street, an engine needs high air velocity below 4,000 rpm. And contrary to the bigger-is-better philosophy, you need smaller intake runners and valves, not bigger ones at this operating rpm. The restriction from smaller runners and valves gets air velocity up and more air/fuel in your combustion chamber for maximum power for those stoplight to stoplight kind of performance your street customers crave. The down side of this is the restriction becomes power robbing above 4,500 rpm because the engine starves for air.
Conversely, in racing you need a lot of air at higher rpms, say experts. This calls for larger runners, bigger valves, compression ratios above 10.5: 1 and porting. These give very good air flow and velocity above 5,000 rpm where you really need the engine to breathe. For the street, this big combo would give your engine poor throttle response, low torque, and would be generally not much fun for your customer to drive.
For additional suppliers of aftermarket performance cylinder heads, be sure to use the Online Buyers Guide.