Horse Power Potential of Cylinder Heads
Okay, Fair enough that's just what the thumb rule estimates, although I don't think I could get there with a pump gas build and using the the intake manifolds on my approved list (Per SVRA: LD4B, LD340, Performer, or Performer RPM; no Air Gap allowed). Frictional losses are pretty minimal in my motor, we didn't coat the pistons but there's roller everything, the rings are low tension, the oil clearances are large, and the pressure peaks at about 55 PSI hot at 6500 (I have strict instructions not to hammer on this motor when the oil temp is below 140). It's been together about a year, has done 3 vintage race weekends at Summit Point, WV ( I've burned through about 80 gallons of 93 octane up there) and 7 autocross events without a hick-up!
A little more tech... Estimating the RPM where peak power will occur based on intake port flow (good for sizing heads to the motor and intended use):
RPM at peak horsepower = ( N / one cylinder displacement (ci)) x CFM
N = 2,000 @ 10" of water
N = 1,267 @ 25" of water
N = 1,196 @ 28" of water
more airflow available to the cylinder, the higher the rpm required to reach peak
horsepower for that head at a given displacemnt.
So for my 318 actual peak HP would be around 7014 RPM [(4.0.75/ 1196) 239] and the same head on a 410 would peak at 5577 [(51.25/1196) 239] or so. Guess my 'teen would like more intake manifold, but I'm rev limiting it to 6800 anyway! Of course thumb rules are just approximations. ;)
Dave
I agree with absolutely everything you said especially the comments about flow test and dyno results. I'm usually a skeptic when it comes to guys and shops chest thumping and touting those figures and all that's why.
But I don't agree with this: " (these will support no more than 497 HP)"
If one builds a combination that is highly efficient - not just in airflow but in combustion and limiting pumping and frictional losses - you can exceed that number. Such an engine in a V-8 factory-type package is a compromise in terms of longevity and costs, but that figure can be exceeded fairly significantly if you control the things that work against power getting to the crank hub. That's the line of thinking behind any successful Stock Eliminator engine builder and many FAST class builders.