I agree with SubiGt that airflow numbers alone are almost never the end of the story. There are many subtleties, not all of which are clear in our "quick-n-dirty" testing (meaning a few flow bench tests and a coupla dyno tests).
SubiGt:To answer some of his questions, the flowbench had to be really cranked up to keep up with all these systems. The instructor noted that this stock setup was one of the best flowing OE setups he has seen.
The results are corrected to 28" H20, but tested at 20" or 10 ". The one class tested at 20 and the second at 10. exceptions were a few situations where the assembly had too much flow, such as the Brute Force and the stock housing without the snorkel or silencer, which were tested at 15" by the first class. Most people agree that the closer you are to 28" the more accurate the results and in this case, we were able to note the "pucker" in the Downspout Connector at 20", which was not apparent at 10".
While we did not measure the time it took to stabilize the flow, it seemed very fast... just about instantaneous. Velocity can be roughly calculated from the actual CFM, can't it, but I don't know if that's an accurate way to do it.
It would be interesting to run the modified air tube with the silencer chambers removed. I'm not willing to modify mine, but if someone wants to let me borrow one, I'll get it tested. Would be really interesting to find a way to test the system plugged into the fender.
88Racing: I'm not convinced (willing to be, but have not as yet) that there are notable differences in power between metal and poly tubes. In "Forum Poster" type racing, of course, every fractional difference is hotly debated. I've discussed this with several engineers and they say, yeah, there is a tiny difference but the air is moving to fast to pick up much heat from a smooth tube. In the OE, plastic is used more as a weight saver and production expedient.
Also 88Racing: I not clear on what you mean by "more air thru the stock setup" ? Yes the stock Motorcraft air filter seemed to flow a little more than the AEM panel. Was that what you mean? Or was it that the stock setup was very close to the modified system. Note that in #6, we removed the rubber downspout adapter and that's when the modified system exceeded the stock by a little.
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!
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