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JohnJL JohnJL is offline
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Join Date: Jan 2005
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Originally Posted by copbait73 View Post
The centrifugal compressor is significantly more efficient at compressing gas than lobed type type blowers so the compressed air is cooler from a turbo than a lobed supercharger.
I am no scientist but I understand this is still a hotly debated topic. I am not sure there is 100% consensus on the point of efficiency.

centrifugal compressors (usually exhaust-driven turbos but also belt-driven units) and screw/lysholm compressors function very differently. One difference is that the turbo "crams" air into the manifold where the buildup of air creates the measurable "boost." On the other hand autorotor superchargers compress the air within the unit as the "pocket" of compressed air travels down the lobes. The air then exits into the manifold "pre-compressed." The air sometimes then "pops" out (that distinctive supercharger sound) and in that "pop" is the expansion of that air pocket. That expansion absorbs heat (cools the charge) somewhat from the high temp it was while inside the supercharger.

Their impact on driving behavior is also significant. Lots of time and money has been spent on anti-lag strategies but there is still something to be said for the instantaneous off-idle power you get in a well-executed supercharged application.

As far as which delivers a cooler charge I am not in a position to opine, but I can share that I'm seeing a total 10 degrees C above ambient on 12.5lbs boost with an air-air Bell intercooler.

Anyway, there are there are ever more super- and turbocharged cars out every day which is a good thing. It is interesting to point out that neither turbocharging nor supercharging has developed into a monopoly...and I love the fact the new Audi RS4 with its supercharged 3.0L is faster, more powerful and MORE EFFICIENT than its 4.2L NA predecessor.

2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 02-10-2010, 03:24 PM
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