68bigblock

I have been told by a race engine builder that you can get more horsepower out of oval port heads versus Square or rectangle port heads. He proclaims that Leindenfelter proved this in one of his books on building race engines. Is this true? If this is so, why are all old corvettes with high horsepower ratings have square port heads?

comp

are you looking at stock, aftermarket, iron/alum. low-end /top-end

The Green Rocket

You will find that this is a debate topic of long standing dispute. I almost think a whole book could be written about the ins and outs of oval vs rec vs roval.

Please remember that a tremendous advancement in the understanding of building engines has occured during the last 40 years. The parts, and parts combinations, that now exist weren't even dreamed of when the Rat made its debut.

Most of the original reasons why oval ports got secondary billing was:
1) Oval port engines had a hydraulic camshaft limiting rpm vs a solid rectangular cam.
2)Oval port heads had smaller valve sizes vs Rec heads, limiting airflow and power potential.
3) Here's a weird one - a rectangular intake installed on an oval port head engine will make more power! Even with the port mismatch! The factory oval port intake manifold was plenum volume restricted.

I say that a person should use whatever they have, spending money on a different set of heads may not be the best use of engine building funds.

That said, my rectangular port 496 made 495 lbs torque starting at 2,500 rpm, peaking at 602 tq at ~4,800 rpm. Just goes to show you that conventional wisdom, holding that rec ports don't make good low rpm tq, is not the end all be all.

Thomas

68bigblock

My 68 427-390hp block has a crack in the cam journal and as of today I have not found anyone who can repair it. So, I went out and purchased another 68 427 engine, and I would like to build this engine close to stock where I'm using number matching heads but would prefer building this engine with more horsepower. In 65-71 all high horsepower big blocks had square port heads. So, I was thinking about purchaseing a set of 840 square port heads that would match my engine numbers and give me a horsepower kicker at the same time. Currently the new 68 427 engine I purchase has a set of 1974 454 "781" 113cc oval port heads on the engine. I also have the original set of oval port heads that came with the car orginally which is a set of "215" 100.9 cc Oval port heads.

I want this car to look original but I also want it to get down the road.