Big heads are okay with a small cam - but why?

[302tt]

I have read a couple times now that you can 'get away' with having heads that are too big for your engine if you keep the cam duration reasonably short. Can anyone confirm if this is true and explain why? Or any examples would be great.

The reason that I ask is that cylinder heads are expensive so I only want to buy them once. Cam's are cheap so I could afford to experiment a little. I want to buy heads that I can grow into as my engine evolves in who knows what direction.

Combo is a 302ci Ford and I am looking at the Trick Flow high ports (190cc inlet IIRC). May end up as a turbo 347, but that could be years away.

Thanks

[rookie]

Even with a small cam you can hurt power with too much port volume, check out this article and #8 also.

Porting School #7 - Power & Port Volumes

[302tt]

Thank for the link - it was a good read, but it did not say much about how the optimum head selection might be a function of the cam duration.

If there is less time to fill the cylinder then the velocity must be higher with a short cam so you would need a bigger head. Right?

For example, in the article the cam duration was 224 degrees at 0.050" and the best head looked to be the one with 200 cc intake volume. If the cam duration was 10% less (202 degrees at 0.050") might the optimum head have been 10% larger (220 cc) to keep the velocity about the same?

[rookie]

My understanding in that situation is that the valve would close before the bigger head would reach max velocity and cause fuel fall out and poor atomization.

It would be better to opt on the side of the smaller head and save $ for porting at a later date if you wish to increase power later.

Big heads always make for a lazy motor and that’s not good in a street/strip combo.

All out race Big head, Big cam and spin the $#!+ out of it.

[rookie]

Here is another where Dusty made 580 horse with a 195 AFR head.

Product Review #4 AFR 195 Comp Eliminator Heads

[Cammer]

Here is a link related to this thread:

PipeMax Simulation of SAM 400 EMC - Speed Talk

Interesting reading and a good look at Larry Meaux's excellent PipeMax software.