[PurelyGTO68]

I was looking through one of my old books written by the guys at H-O Racing Specialties and found some flow graphs and section views that compared various Pontiac cylinder head types.

I had always thought the 'magic' with the round port heads is in the exhaust port just because that is easily identified as being different. However, now that I look at them a little more carefully....the intake ports are quite different then the D port heads. The flow graph shows the round exhaust port flows about the same as the D port head and when I compare the two....the port is only round right at the exit. The rest of the port appears about the same (at least when I compare my RAII heads to a pair of 670 heads that I have available....).

So, it appears the magic is in the intake ports instead. Does this sound correct? If so, I wonder if the stock cast intake manifold is able to flow enough to meet the demands of the RAII and RAIV heads. Any thoughts on this?

If the flow chart is correct, there appears to be a sharp drop in flow around the .460 lift mark (except for the 73 455 SD heads....those things just keep on flowing as lift increases....). Any theories as to why this occurs? Just trying to learn a bit more about the RAII and RAIV engines.

Thanks