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Originally Posted by RH77
I thought I'd resurrect this thread with some MAP questions.
After a few hundred miles of observing the MAP figure on the SG, of course decel = lower numbers and higher FE, and accel = higher numbers, lower FE. Just brainstorming, it is possible reduce the manifold pressure at higher RPMs, and still maintain stoich? I'm not sure how you would do that without increased vacuum or some such.
...or is MAP a result of what is happening, and cannot be manipulated unless forced induction is added to increase the figure, and negate FE gains?
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I'm not sure what you mean buy "higher numbers" and "lower numbers." I take it you mean lower numbers as closer to atmospheric and higher numbers as higher vacuum...
Ideally, you don't want to pull a vacuum at all. It requires energy to create a vacuum, which is expressed as pumping losses. Pulling high vacuum during acceleration is a result of a nearly closed throttle plate. It's like the engine is sucking through a straw.
I believe part of the reason why "Atkinson cycle" engines are so efficient is that pumping losses are heavily reduced. Charged air is sent back into the intake manifold destroying the vacuum. The same can be done with a supercharger (whether it be turbine or engine-powered).
The killer determination is figuring out whether the method of destroying that vacuum absorbs less energy then the formation of the vacuum in the first place. If it absorbs more energy, you're wasting your time.
BTW: Technically, if you are using a "supercharger" to bring MAP to ambient, it isn't a supercharger.
supercharger: a compressor that brings MAP > 1 atm
turbosupercharger: a compressor that brings MAP > 1 atm via a turbine
normalizer: a compressor that brings MAP = 1 atm
turbonormalizer: a compressor that brings MAP = 1 atm via a turbine
Generally, normalizers are used on aircraft piston engines to combat the effects of decreased density with altitude.
- LostCause