Used Freescan for the first time today, and looking over all my numbers... one thing looks a little odd, maybe its normal. I haven't seen anything that discussed a small drop like this:

WOT:

RPM -- MAP

3025 - .98
3700 - .97
4100 - .97
4725 - .96
5000 - .95
5500 - .94
5700 - .93

Its a small drop in pressure, but maybe this shows an intake leak or something else? Not sure if that is normal or not...

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FormulaV8.com · 1994 Formula · A4 · 3.23
13.45 @ 102.5 MPH w/ 1.9 60' | 267 rwhp | 307 tq/lbs | 3535 lbs
"I know for a fact he is NOT an Easter bunny"

 

You are simply seeing the effects of increasing pressure loss in the intake track, based on increasing air flow with increasing rpm's. If your engine is shut off, and you open the throttle all the way, MAP should equal BAR (barometric pressure)..... there is no difference between the air pressure surrounding your car, and the air pressure inside the intake manifold. When you start the engine, air starts to flow, roughly in proportion to RPM (this ignores volumetric effciency, but that's OK). Since pressure is lost in the intake ducting, filter, MAF, TB, whatever... in proportion to the square of the velocity, as the flow increases, the pressure lost in the intake track increases, and the portion of BAR remaining in the intake manifold is less.

I don't believe the decimal point (e.g. .98) belongs in your data.... the units are kiloPascals (kPa), and typical barometric pressure at sea level is in the range of 100-103kPa. Intake manifold pressure (MAP) will always be slightly less than this when the throttle is wide open, and the engine is running. If you feel you are losing excessive pressure in the intake track at high RPM, disconnect as much of it as you can... e.g. - filter, ducting.... and see if MAP stays higher. If it does, you have excessive restrictions in your intake system, that may possibly be improved with a better/larger filter, better duct, etc.

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Fred
94 Formula A3+1: 381/TH400+OD/N2O

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[This message has been edited by Injuneer 94FormM6 (edited September 13, 2002).]

 

So its normal, cool. Thanks for the explanation. I'm trying to learn what normal numbers should be for all these various readings that I have access to now. And that slight decrease in MAP while RPMs increased just looked a little funny.

I guess you could also use these readings to compare before and after intake modifications (CAI, TB, etc).