A Larry Carley article-head choices good read
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Re: A Larry Carley article-head choices good read
, many heads can deliver impressive flow numbers. But if those numbers are rated at .700 inches of valve lift and the engine you are building only has half an inch of valve lift, you are better off choosing a head that flows best at .400 to .500 inches of valve lift.
Now the issue is if cam is only .500, what good is .800 lift numbers? Answer is depressions on running motors exceed flowbenches depressions of 28" h2o. This means air can choke in flow sooner as high depression differential the air speed can increase. So a head that backs up in flow on bench at .800 may show backing up sooner at say .600-.700" on running motor. This seems to be a complex issue that is effected by many things including fuel mixture, manifolds bolted to heads and valve motion from the cam.
So you would think you'd want to pay alittle attention to head flow way above your cams lift number... But ask some builders or head guys, sometimes motor combo still works and makes power even if port looks bad on bench. Again i think thats where cam and manifold effects alter performance of head port to make it work. There was an excellent example and discussion of this at chevelles.com called lessons learned.
Now forced induction cars in high boost absolutely want stable port to high lift ranges. Sacrifice low and mid lift flow numbers for increased stability. Dense air doesnt turn any better than atmospheric air. Infact it should be worse.
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Re: A Larry Carley article-head choices good read
Good article, can't disagree with a single word he says. Pretty basic stuff mostly, alot of just common sense, good for somebody that doesn't know hardly anything to start out with, that will help keep a n00b out of the weeds.
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