Quote:
Originally Posted by Jim Allen
JackandJanet: The theoretical airflow number I gave is calculated. The formula is :
CFM= RPM x DISPLACEMENT /3456 x VOLUMETRIC EFFICIENCY
I used 5500 rpm as a reasonable maximum and was generous in giving the fairly free-breathing modular a 90 VE. 85 percent would be more real world but would drop the CFM result. I gave it .90 to factor in some other mods that would increase airflow a little, such as a free flow exhaust and a program. At 100 percent VE, flow would be 525 CFM, still under what the stock system flows.
5500 x 330/3456 x .90= 472.656 CFM
My conclusion is that the stock intake is pretty darn good and can support some extra horsepower. A CAI, as SubiGt noted, tends to lean the mixture a little and that's where most of the power is. Thing is, your Edge or Grypon does the same thing and unless you need the extra airflow, I don't think the two things "stack" all that well. Bill has to essentially richen the mixture with a CAI because the combo may lean it too much, thus negating a big part of the advantage the CAI offers. Bottom line, IMHO,if the stock intake system has the airflow, you may not need the CAI when running a mild program.
I almost forgot: Remember that this is a throttled engine. Everything we are discussing is relevant only at WOT. The throttle plate is the main restriction in any engine (how much time do we spend at WOT??) and beyond that it's the intake valve!
|
Jim - I was pretty sure you were getting the "required" airflow number this way and I can't see any other way to get it. I would have used an RPM figure of 5000, since power seems to drop off above that, but this would only reduce the airflow needs.
And, we've already agreed that this mod's effects would only be seen at WOT/high RPM.
But, I'm still left with the fact that Bill has measured higher power with the restriction removed.
I wonder if this is an explanation? The possible air volume requirements may well be supported by the stock intake, but, with a cross-sectional intake area of 3.14 sq inches the flow velocity would have to be higher than the velocity with the restriction removed and a cross-sectional area of 7.07 sq inches. Higher velocity equates to lower static pressure. Lower static pressure available at the intake port, equates to lower absolute compression (relative to sea level pressure), similar to what you'd get running at altitude in the high Rockies. Lower compression means lower power.
But, I sure don't like the way the downspout approach "puckered". I think the inlet HAS to be rigid.
- Jack