When choosing a cylinder head for a specific use, air flow numbers should never be your first consideration.  In a nutshell, port size and shape are everything.

Too many enthusiast magazine writers are transfixed by air flow testing and try to apply the numbers, somehow, to the selection of heads, camshafts and other parts.  Convincing as their arguments may seem, comparing air flow numbers amounts to nothing more than “racing” one flow bench against another for high numbers.  Most flow bench data means nothing to anyone except the bench  operator.

Total Flow Products uses a model head that is never changed, to calibrate our bench during every test.  Our port entrance fixtures are solid wood or plastic and are dedicated to each head tested.  A bore is chosen to match your combination.  All said, an approximate idea of your application remains the first imperative to building or selecting heads, not air flow testing.

Since many racers usually have little information but a writer’s advice to rely upon, when choosing cylinder heads and high performance parts, Total Flow Products has developed a series of questions that will always be asked of customers calling for cylinder head selection advice.  These questions will define what is wanted and then determine what is actually needed.

1.    Vehicle use?  What are you doing with the car – is it a daily driver, street rod, street-strip machine, drag racer, oval track car, road racer, puller, boat, etc.?

2.    Application?  What you are going to do – street performance only, trailer towing, more drag than street use, bracket racing, dirt or paved oval, truck or multi-engine tractor, drag or ski boat, etc?

Answers to these first two questions indicate the extent and frequency of maintenance the engine will receive – important factors in component selection (metallurgy, design, manufacturer, etc.).

3.    Engine size (cid – cubic inch displacement)?

This is the starting point for determining how the combustion chamber will be prepared, the size of the intake valve and the size and shape of the intake port.  The exhaust port and valve are not significant factors, at this point.  The final configuration of the head and both valves will be determined by the remaining questions.

4.    Operating rpm range and how will the engine cycle through the range? 

This relates directly to how the car will be driven.  A small block Chevy, for example... two drag racers build 400 cid engines. Racer #1 has an automatic transmission, single 4 bbl carburetor, a moderate hydraulic roller cam and will run to 7,000 rpm, maximum.  Racer #2 has a 4-speed transmission, single 4 bbl carburetor, .700” lift roller cam and will run above 10,000 rpm.  Very different intake port designs are necessary for each application.  The ports may flow similarly, at certain points through the flow curve, but a design maximized for 5,500 to 7,000 rpm will not work efficiently at 10,000 plus.  The same holds for an oval track racer with a similar engine.  The operating rpm range from a corner exit to the end of the straight may be the same as drag racer #1, but the oval track car has momentum, doesn’t shift gears, has a longer acceleration period and may be fighting greater aero forces.  NEITHER drag racing port will work for this application. 

5.    Camshaft type (hydraulic, mechanical, roller, etc.) and approximate lift to be used?

Basic camshaft selection has more to do with the frequency of maintenance than an exact lobe or centerline.  Back to our example… racer #1 chose a hydraulic roller because he probably wants to leave his engine together all season.  Racer #2 chose a mechanical roller because his engine will be taken apart every so many runs.  When it is apart, we can service his heads, as needed.  Therefore, we can recommend a more “cutting edge” head and preparation for #2 and a durable head with robust preparation for #1.

6.    Induction?  What type of system will be used – single/multiple carburetion, fuel injection, turbocharger, supercharger, manifold type/design, etc.?

How the fuel/air mixture or air alone arrives at the port is a crucial factor in designing the port itself.

7.    Fuel?  What type is planned – gasoline, alcohol, nitro, diesel, etc.?

Once these questions have been answered, and what you want is understood, we can discuss what you will need.  As is often the case, wants and needs can be very different.  We want you to be 100% satisfied that Total Flow Products delivers precisely the performance you needed.  That’s why we need to precisely understand the components, use and maintenance described by your answers.