[Adam C.]

So now for what is the most exciting topic to me, cylinder head flow. We already showed that you really can't have too much exhaust valve flow, but is this true for the intake valve?

For this test we are using the single plane manifold in the previous example because it offered more power than the EFI manifold with longer runners. Now we are going to vary the intake valve flow up and down by 25%. This just so happens to equal 180 CFM on the low end (GT40 iron heads) and 300 CFM on the high (TFSR).

On the low end, higher flow means less torque. This is because we have a cam with a good amount of overlap and it is letting some of the fresh air in the cylinder reverse and go back out the intake before the intake valve closes. We could probably make the same power at low RPM with all three heads by adjusting the cam, but again the top end would suffer.

On the top end, more flow is better, period. There is this myth that you can have too much flow for small engines, or those with low compression, or low RPM, etc. This is simply not true. The reason these engines often perform poorly is because the PORT DIAMETER has been significantly increased, loosing flow velocity and shifting the natural frequency of the induction system too high. At low RPM these engines suck because they have a cam with an intake valve closing event that is probably too late.

This is the difference between recognizing patterns, and examining things systematically. Fortunately in engine simulation you can change exactly one thing at a time and see the effect of that one thing, even if it may not be possible to implement in real life.

So with the TFSR's (or AFR 205's for Ron since he is so smitten by them [img]/ubbthreads/images/graemlins/grin.gif[/img]) our little 302 is rockin at 7000 RPM. We're talking nearly 110% vol eff! Just for comparison, our original 5.0L with a complete aftermarket mustang exhaust system managed about 325 HP at the flywheel. Our new configuration with the single plane manifold, TFSR's, and GT type exhaust and no mufflers is now sporting about 465 HP. This is with with a very streetable 10.3:1 compression and a relatively mild hydraulic roller cam (wich would probably cause valve float above 6000 RPM in real life).

There is not much left now but the cam, compression, and everybody's favorite, displacement. Do we press on?