Did you guys catch the Horsepower TV show over the week end. It was the only one I could say was real good. They went thru the pocket porting and cleaning up of SB Chevy cylinder heads.
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Re: Horsepower TV
The single best way to make "more power" is to massage the heads. Leave everthing else OE and the engine will look OE, idle like OE, and have the same general operating behavior up to about 4000 revs, but above that it will keep pulling strong to the redline or above.
Figure about 10-15 percent more top end power, and no only does peak power improve, but the peak power "sweet spot" improves by extending the useable power range another 500-1000 revs.
This applies to base, SHP, and FI engines as long as they have full dual exhaust systems.
Unfortunately, the single catalyst system that began in 1975 will not respond very well to any internal changes. These exhaust systems have so much backpressure that pumping loses eat up most of the internal flow improvements that make more power with a low restriction exhaust. The pre-catalyst Corvette exhaust systems were good (2" pipes or 2.5" on big blocks) to very good (2.5" pipes with a small block).
The best OE exhaust systems only generate about 3 psi backpressure with a massaged SHP small block - and up to 6 with a massaged SHP big block which is getting a bit restrictive.
Dave McClellan in his book stated that the single catalyst exhaust added about half an atmosphere backpressure - that's about 7.5 psi - and when you end up with 10-12 or more psi backpressure the parasitic pumping power is HUGE, which is why seventies vintage Corvettes had such lackluster net power ratings and can't be significantly improved without adding a much lower restriction exhaust system.
DukeComment
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Re: Horsepower TV
You've got my interest up on the old 461x head. I think I'll put one of these on one of my flow benches and fool with it . Can you expect to pull 150 CFM w/1.94 intake @ 28". What are good numbers on these heads ? stan 19259Comment
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Re: Horsepower TV
Thank you Duke Williams and all for explaining the advantages of cylinder head porting.
Ray
And when you get the choice to sit it out or dance
I hope you dance
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Re: Horsepower TV
150 CFM? You're talking about the exhaust side, right?
See the Fall 2010 Corvette Restorer. There is a table of head flow data for Flint-built and massaged 461 and 462 heads. I don't have any data for 461X, but my expectation is that the slightly larger port volume will flow about the same as 461/462s, all in OE form, but might be better when equivalently massaged and may outflow 2.02/1.6" 461/462s even with the original 1.94/1.5" valves.
BTW, I NEVER recommend increasing the valve sizes if the heads originally have the 1.94/1.5" valves. The increased propensity for the heads to crack between the valve seats far outweights the marginal increase in flow.
What kind of flow benchs do you have?
DukeComment
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Re: Horsepower TV
Could you post a link to the DVD, please?Comment
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Re: Horsepower TV
Dan,
Here you go:
JoeComment
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Re: Horsepower TV
I use an old fashon VCR to record. I will save this episode.Comment
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Re: Horsepower TV
Click on "Chevy" under "Cyl Head Flow @ 28 inches water column", scroll to 461 cylinder head.
I know someone who achieved 220/195 @ 0.5 and 224/201 @ 0.6 with 1.94/1.5 461's. Those are impressive flows, and the heads were ported beyond the pockets. I achieved 255/208 @ 0.6 with 2.02/1.60 461's after I fully ported them and opened the inlet runners to nearly 180cc's.Comment
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Re: Horsepower TV
Joe Ciaravino, Those are very impressive numbers. I guess the Chevy S/B has had more attention than the human heart. Thanks much stan 19259Comment
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