Quote:
Originally Posted by Piotrsko
Superchargers would be belt drive? So some loss when adding boost from drive system.
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The concept of supercharger would be belt drive, and that's because you'd want boost down low like 2500-3000 rpm. I'm sure turbo's can be sized so they boost pretty low, but I think they are more 4000-8000+ rpm type of range typically.
Quote:
Originally Posted by Blacktree
Generally speaking, adding boost to a gas engine increases BSFC. You have to run it a little rich, to avoid knock. A diesel engine is a different story, because knock is not a concern. So you can run it super-lean.
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There's a lot of factors involved with boosted engines. What's your source for the increase in fuel use? Just wondering if there's a theory behind it, personal experience or what.
Engines normally retard timing to prevent spark knock, that's how it's done on Toyota's at least. My 1990 Lexus LS400 is 10.5:1 compression ratio and calls for 90 octane min. I sometimes run 87 octane in it, and I can feel the timing being pulled (knock sensors pick up the knock and computer responds by adjusting the timing). The amount of fuel injected should be more or less the same. Not quite the same as boost, but this same car had a dealer installed option for a super charger, literately a bolt on kit, no tune change to the computer. I don't recall but I'd assume it requires higher octane fuel, but the same system the pulls ignition timing should work with the boost, at least to a point (it's max output is like 7psi).
On the GM side of things, when the engine gets hot, that has a similar effect as higher compression or extra boost, I've seen in their tune tables that they pull ignition timing, but I don't remember seeing anything in the fuel table for the same region. Again, not directly boost related, but somewhat related, preventing spark knock.
One benefit of having a boosted engine (super charger or turbo) is the fact you can use a much smaller engine to put out the power of a bigger engine. I don't think too many cars use that concept though, but I'd think it could potentially help FE having a little 1.8L making say 200hp with boost vs an 4.3L GM v6 which makes about the same hp. I would think there would be less losses with the inline 4 and smaller parts than the big v6. I guess a better example would be like a 500cc motorcycle engine powering a small car and having around 100hp (just guessing, but something like 15lbs of boost, it would be clearly a pretty hot setup). The Corolla 1.8L in my 1997 was around 110hp.