WOT MAP Values(kPa)

[Black02SS]

I am wondering why i see some guys that are seeing values in the 98-101 range at WOT. I have personally never seen anything over 98 on mine with the average being 96-98. Why the difference and what would cause it?

[trudynosports]

On a couple blower cars I've ended up with numbers reaching 110 in VE. It is possible for an engine to be more than 100% VE, especially power adder cars. The 110 in VE is tuned for an AFR of around 11.5:1 in WOT and again most were turbo cars.

Aaron.

[Black02SS]

Thanks Aaron, but I am refering to straight N/A cars with no adders.

[dfe1]

The original question pertained to MAP- manifold absolute pressure-, not VE, which are two entirely different variables. I've also rarely seen MAP numbers at WOT much above 96-98 kPa. I think there are a few valid reasons for this. Depending upon altitude and weather conditions, barometer readings may be substantially less than anticipated. When ambient barometer readings are converted to kPa, you'll find that they may be below 100kPa. In a naturally aspirated engine, max kPa obviously can't be more than ambient barometer (ambient air pressure). The standard reference pressure at sea level is 29.92 inches of mercury, which equates to 101.32 Kpa. That being the case, MAP readings in the 98-100 kPa range are reasonable for an engine operating at or very near sea level. However, it the barometer is only 29.0 to 29.3 inches of Mercury (as it is here in the Atlanta, GA area), the maximum MAP readings-- assuming ABSOLUTELY no pressure losses through the air cleaner, intake tract and throttle body-- will be 98-99 kPa. That translates to realistic readings of 96-98 kPa at WOT. Then you have accuracy and tolerance of the actual MAP sensor to consider.

To avoid chasing ghosts, simply turn on the ignition and link FlashScan with the engine not running. Then look at MAP readings. (Open the throttle slightly to eliminate the possibility of false pressure readings.) Whatever reading you see will be the absolute maximum you'll ever see with a naturally aspirated engine running at wide open throttle. Most likely, intake system restrictions will reduce max kPa readings by 1 or 2 with the enigne at WOT.

I have to guess that blackSS02 does not live at sea level.

[Black02SS]

Well, the altitude here is about 800 feet. That mixed with the hot air this summer, that puts my DA around the 3200 mark. :(

[joecar]

Air filter restriction may account for 2 kPa (barometric air is trying to rush into manifold but is slowed down by air filter);
Try taking a WOT MAP reading (engine running) with air filter removed temporarily (only for this experiment).

[dfe1]

We're at 900-950 feet here in the Atlanta area. I just checked ambient barometer on my C5 (MAP with the engine not running) and it toggled back and forth between 98 and 99, so it's probably right at 98.5 kPa. That equates to about 29.1 inches of Mercury, a fairly typical uncorrected barometric reading in this area. If you check local barometer, make sure you get uncorrected numbers. Standard weather station readings are corrected to sea level. Temperatures are essentially irrelevant as they have little or no direct effect on barometer.