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Originally Posted by LostCause
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...
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Lower MAP figures = lower than ATM, which I assume is considered a vacuum of sorts. My question: when lifting from the accelerator, vacuum is apparently produced, and (assuming the injectors are not cut), FE increases per the gauge.
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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.
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So acceleration closer to ATM is more efficient? This generally happens during WOT -- where the forced induction comes into play in non-WOT applications.
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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
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Still, we're only at the theory stage with this sort of inquiry. I recall a couple years back hearing of a guy with a Civic that ran 0-psi of boost from a turbo to reduce pumping losses or something similar.
Basically, I need more efficient, operability in the low RPM range (1500-2500).
RH77