| Re: Driving impressions with the AFR heads |
Subject: Re: Driving impressions with the AFR heads by BeachBum on 2009/8/18 20:03:04 I think to be fair, if you look at the extremes.... anything is possible. For example take a stout 406 sbc built with a solid roller .750+ lift 280+ duration Joe Sherman type cam designed to pull to 8000 rpm..... and put on a decent set of aftermarket 23 degree heads that say flow around 280 cfm..... the performance results may be along the lines of 10.2 @ 130 mph or thereabouts...... now take off those 280 cfm and put on some 70's smog head that wheezes to max flow of 200 cfm if its a windy day..... that same motor now might only run 11.2 @ 120 mph..... power is completely gone. Now take off those 70's smog heads and put on a bitchin set of aftermarket cylinder heads that flow up around 320 cfm..... and that motor just might see 9.8 @ 134 mph.... So from Joe's perspective, yes in my opinion, you could see 10 mph swings, but it would have to be an extreme and none of the cylinder heads talked about in this thread are that poor in my opinion. The difference between these two test cylinder heads would more than likely be in the 15-20 HP range..... I say this because of the street set-up it is under.... these two same cylinder heads under a rowdy motor could show a difference of 40 HP.... assuming the 2hp for every cfm gained theory..... which is attainable as most engine builders will tell you, but the motor has to be willing and Josh's .570ish lift cam doesn't even take advantage of either of these cylinder heads peak flow area, thus he is more limited to around 1 hp per cfm..... and considering there is a 22 cfm difference in these cylinder heads at .600 lift, and around 12-14 cfm at .500 lift.... on a linear scale, we can say there is probably around 15-18 cfm difference at Josh's cam peak. Which I might add, unless the AFR's were milled to get compression up, that HP gain might be partially wiped out by compression.... (I do not remember what Josh did, but I remember it was going to be like 11.4 cr vs 10.8 or something like that) The test in itself has lost some definitive value due to test conditions and unknowns at the start such as what was done to the Trick Flows..... the company that flow tested them, I remember said they were thoroughly ported, but hard to see due to bead runover, but yet Josh had paperwork for just a little clean-up.... I dunno. The one thing I will say, as all true racers will tell you that are et hunting.... we'll take hundredths at a time if thats what is available.... a gain of 1-2 mph on any given day with a bolt-on performance item like a cylinder head is a good day and can literally mean a 15-35 HP gain dependant on how fast you were going in the first place. The guys that race in heads-up series are begging for .1 and .2 mph gains, let alone a full 1-2 mph. It is a defnitive differnce in power to most serious racers. I think the one thing some might lose sight of, is the faster you go, the less HP has an effect..... many believe a 10 hp gain will give you a tenth... and it typically will on a 14 second car..... but on a 10 second car, its more in the 4 or 5 hundredths area..... on a 7 second car, its thousands or two and may be unnoticeable even to the keenest eye... but on a 19 second car, you could see 2 tenths gain from that 10 hp gain. But, I don't know, the above is just my opinion, I am guessing like everybody is. |
