Quote:
Originally posted by srv1
i dont understand your figures. only 68.4 cfm's? am i missing something? isnt that really low?
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Yes, I understand your confusion. I didn't believe it at first, either, but that's what I got. I even tried different flow ratings on the machine and calculated the same thing (within 1-2 CFM). The numbers are for individual ports, not the entire intake bank for one head. So, if you want the total intake capacity for a 5.0L with E7TE heads, it's (68.4 * 8) = 547.2CFM, which DOES make sense.
This leads to my other point about E7's: their airflow is apparently, and I mean
by the math only, NOT one of the limiting factors on a 5.0L engine. I know I'm going to catch hell for that remark!
Well, I think the MAJOR difference is that the aftermarket heads flow better at lower valve lifts than E7's do, really. They get that high flow *BANG!* right now. With E7's, you have to wait for the valves to get about to 0.300in open for maximum airflow. That costs time, especially detrimental to power when you're in the upper RPM band.
Using basic internal combustion engine equations, you can see this:
100% volumetric efficiency = 0.5 * RPM * displacement / 1728
= 0.5 * 6250 * 302 / 1728 = 546 CFM
This is pretty DAMN close to the 547.2 CFM (within 1.2 of!) the heads can flow. I believe the trick is to get those valves OPEN to the point they are flowing maximum airflow (at least 0.300in), and
keep 'em there for as long as it will draw in or expel a charge. It seems like what Comp Cams wanted to do with the Xtreme Energy cams: more area under the curve.
Mebbe this goes to serve another point: Ford did their homework when they developed these engines. I'm still trying to figure things out, and I'll keep you guys up to date if I come across anything noteworthy. Mebbe it's the intake keeping it held back, too???
Anything I flow less than 547 CFM will be suspect and held at gunpoint.
