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Old 09-05-2012, 03:18 PM   #9 (permalink)
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Originally Posted by caliboundranger View Post
I'm still working on understanding the warm air intake bit. I understand that heat is power and heat soak through and out of the block means losing power. I know thatis one compromise of aftermarket aluminum heads; they are a giant heat sink but they offset the loses by extraordinary flow and weight loses. I feel like the more power you make from the same cu. in. is increasing effeciency. ie.. you getting more with the same size. hence why turbo cars make huge power and can still get great fuel mileage. My thinking is that the bsfc best effeciency for that motor may just more on the chart to a different rpm and possibly load. But i'm no genius, just thinking outloud and trying to put 1 and 1 together and have it equal 2.
It isn't as complex as that, it actually has to do with the throttle valve in the throttle body restricting the air intake. Massive pumping losses exist trying to drag all the air through the restriction that is the throttle itself. If you have cold air, it is denser, so the engine needs less of it for a given power load, so it closes the throttle valve a bit more. If you have warm air, it is thinner, so the throttle opens more, less pumping loss, better efficiency. That's why a turbo engine works well, gives you a lot of power with compressed air when you need it, but when you don't need all that, it is an undersized engine that needs to open the throttle farther to keep up. The wider open throttle is key.

Diesels get good mileage because they don't have this pumping loss, they run wide open all the time, power is controlled by the amount of fuel being injected.

The key to the BSFC curve is if you use a small engine in a car, it is operating closer to its ideal island of efficiency, if you have an engine capable of lots of power, it is operating far outside it's peak efficiency at normal highway speeds.

I think too, if you do a warm air intake, it wouldn't slow you down when you need the power because you'll be pulling in so much air, it won't have time to get warmed up, so you'll still have close to peak power when you need it. Remember, 99.99% of the time, automotive engines are not using their rated output.

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