Ported GT-40x heads vs AFR185

[KevinM]

hi-tech,

This is a lot more involved that I think you are aware of.

If the heads really do flow 270 / 170 @ .550 lift. then the intake is about the same as an AFR185 but the exhaust is down about 20 from the AFRs.

Even if those estimates are correct, we don't know the flow at .300" and .400" lifts, which are very important for understanding the real flow of the heads. The smaller valves are definitely likely to be an obstruction and are one reason I am a little dubious of those estimates.

Smaller valves do not improve flow at lower lifts. The AFRs outflow GT40s from .100" lift up. and have much better midrange performance.

I also have to question the "Nascar Guru" thing. Nascar uses a completely different kind of head with different ports, different valve locations and angles, and a completely different valvetrain. Even if the person was knowledgeable on Yates and C3 heads, that information wouldn't transfer to wedge type street heads.

There is also the matter that people who really do a lot of work on Nascar engines get paid a lot of money for that. It is hard to believe they would be waisting their time porting a set of GT40 heads.

As for cam, how high do you want to turn the engine, and what kind of low RPM bad behavior are you willing to put up with? For a street driven car the Comp XE266HR is a very good cam with the AFR heads. The Comp XE274HR would be better at the track, but will not be a great day to day drivability cam.

If you do go with your ported GT40s, based on the highly questionable numbers we have, you would want a cam with about 12 degrees more exhaust duration than intake. That would have to be a custom cam.

Kevin