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Occasionally6 · 09-10-2014, 08:03 AM

Absent forced induction, the maximum, achieved at wide open throttle (WOT), will be close to the local atmospheric pressure i.e. ~100kPa. Perhaps a little less at high engine power outputs (high MAP & rpm) and air flow rates, where there are some more noticeable losses in the intake ducting and air filtration.

MAP doesn't directly relate to fuel consumption, although in general higher MAP = more fuel consumed. The other main variable is engine speed. If you put those together, high MAP + high engine speed = lots of fuel consumed and vice versa.

Most engines have still have the additional fuel added in with high MAP, especially with engine speed (and therefore power output) towards the higher end of the range. (To control - reduce - the engine and exhaust temperatures.) That will kill engine efficiency with really high MAP. You've probably seen that with open loop and high MAP.

Otherwise the higher the MAP, the lower the difference in pressure between that in the cylinder and on the underside of the piston during the intake stroke. That difference in pressure manifests as work that has to come from the fuel and is therefore unavailable to move the car. MAP corresponds pretty closely to the in-cylinder pressure (which is lower than MAP).

The lowest MAP you should see will be ~30kPa and that with a closed throttle. You may see it a bit lower during an in-gear, closed-throttle deceleration, depending on what the ECU does with the idle control during deceleration.

I expect the load percentage will be calculated based on the current MAP minus the minimum MAP divided by the range of MAP possible i.e. maximum MAP minus the minimum MAP. Like this:

("current MAP" - ~30)/(~100 - ~30)

09-10-2014, 08:03 AM	#4 (permalink)
Occasionally6 Master EcoModder Join Date: Apr 2013 Location: World Posts: 385 Thanks: 82 Thanked 82 Times in 67 Posts	Absent forced induction, the maximum, achieved at wide open throttle (WOT), will be close to the local atmospheric pressure i.e. ~100kPa. Perhaps a little less at high engine power outputs (high MAP & rpm) and air flow rates, where there are some more noticeable losses in the intake ducting and air filtration. MAP doesn't directly relate to fuel consumption, although in general higher MAP = more fuel consumed. The other main variable is engine speed. If you put those together, high MAP + high engine speed = lots of fuel consumed and vice versa. Most engines have still have the additional fuel added in with high MAP, especially with engine speed (and therefore power output) towards the higher end of the range. (To control - reduce - the engine and exhaust temperatures.) That will kill engine efficiency with really high MAP. You've probably seen that with open loop and high MAP. Otherwise the higher the MAP, the lower the difference in pressure between that in the cylinder and on the underside of the piston during the intake stroke. That difference in pressure manifests as work that has to come from the fuel and is therefore unavailable to move the car. MAP corresponds pretty closely to the in-cylinder pressure (which is lower than MAP). The lowest MAP you should see will be ~30kPa and that with a closed throttle. You may see it a bit lower during an in-gear, closed-throttle deceleration, depending on what the ECU does with the idle control during deceleration. I expect the load percentage will be calculated based on the current MAP minus the minimum MAP divided by the range of MAP possible i.e. maximum MAP minus the minimum MAP. Like this: ("current MAP" - ~30)/(~100 - ~30)