Originally Posted By: badtlc
Again, restriction isn't limited to the throttle plate. Is it the most significant? Yes. The air filter is in series with the throttle plate. Any restriction, no matter how small "adds" to the throttle plate restriction along with any bends and drag within the intake itself. The statement that the throttle plate is the only restriction is patently false.
Shannow stated:
Originally Posted By: Shannow
Manifold absolute pressure is what it is due to (ignoring altitude for a second) the air filter and assembly DP, and the throttle plate position.
More restriction in the air filter means you open the throttle more...for the same manifold absolute pressure
He didn't state the throttle plate was the ONLY restriction.
I stated:
Originally Posted By: OVERKILL
generally the biggest restriction in the intake tract is the throttle blade unless we are at WOT and then often it is a silencer of some sort either before or after the filter.
You'll note I also didn't state that it was the ONLY restriction, simply the biggest (unless we are WOT).
The point Shannow has made is that what you are controlling is MAP. This is done, unless we are at WOT, with the throttle blade. To obtain a given power level at a given RPM, you are targeting a specific MAP point. The ECM either measures this directly (with a MAP sensor) and fuels accordingly (factoring in blade position and everything else of course) or it extrapolates it from the data it gets from the MAF, which directly measures airflow in the intake tract BEFORE the throttle blade but AFTER the filter.
Filter restriction is only SIGNIFICANT when it affects MAP at WOT, which will in turn reduce power output. Anything below that, it is transparent because MAP is being directly manipulated by blade position.