Quote:
Originally Posted by Skip Fix
OK some flow numbers same day we flowed these @ 10" multiply 1.67 for 28" numbers
#96 unported(identical numbers for an unported 6X-8)
0.1 47
0.2 81.6
0.3 100
0.4 110
0.5 113
0.6 115
197 unported
0.1 51
0.2 87.7
0.3 108
0.4 119
0.5 124.4
0.6 126.5
mildly ported 72 HOs-on a friends Formula now that was just in HPP
0.1 49
0.2 82.6
0.3 110.6
0.4 128.5
0.5 131.6
0.6 131.6
stock 614 flat valve-better low lift than tuliped higher lift the same
0.1 53.7
0.2 86
0.3 116
0.4 121
0.5 127
0.6 125.6
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unfortunately, flow numbers at anything less than 28", can be misleading, and give an incomplete picture. here's why- 2 different heads that visibly have dramatic differences in port shape, valve size, port size, can flow the same at lower pressures. as the pressure is increased towards 28", that's when the differences show up, and a good port starts to flow more. beyond 28", there's not much difference. and that's how the 28" standard was discovered, by farmer cut and try method, by Smokey Yunick, with back to back dyno tests on the same heads to correlate. i.e. if the head flowed more, he double checked and verified it on the dyno, as making more HP too.
He laboriously took different ports and flowed them at increments from very low pressure to very high pressure, and found the sweet spot where the flow numbers reflect real HP gains on the dyno, and a good flow number therefore meant a good port. that pressure drop is 28". numbers at 12" can't be relied on as confidently. reason being you may have a head that flowed average to all the others at 12", but it would really take off at 28". that's the pressure drop that correlates with more HP on the dyno, as the flow numbers increase.
this is also where the late Pete McCarthy dropped the ball, when he did the Pontiac Ultimate Cylinder Head articles on HPP decades ago. Had he insisted flowing the heads at 28", that would be one heckuva an achievement. but no one is perfect. It was one of his few errors as a Pontiac journalist and writer and historical information. That's because Pete never read Smokey's book, Power Secrets. If you don't commit that to memory, you're a babe lost in the woods. They're all V8 engines breathing the same air on the same planet. Smokey ran Pontiacs in NASCAR from 1958-62 and dominated with them, and that's why. He had already built hos own flow bench and was using it and his dyno, on the Pontiac heads and engines, which at the time were the SD389/SD421 configuration. He was working with Pontiac engineering, advising and telling them what the engines needed, to be competitive in NASCAR. That's where the SD421 heads came from, and why the 980 heads were as good as they were.