Re: [ST] Supercharge vs Turbo

[Paul English <tallpaul@xxxxxxxxxxxxx>]

On Fri, 3 Feb 2006, Jim HIGGINS wrote:

> Properly sized turbo has no added back pressure,turbo is sized according to
> intended use,street,drag racing,ralley,etc.So a good turbo system matched to
> your engine use,compression,etc. will work seamlessly.Look at the
> Mitsuibishi Eclipse,Rallye,Subaru WRX's etc.The added heat comes from
> compressing the incoming charge and is overcome with intercoolers/charge
> coolers.Jim.

No offense, but this is counter to the laws of physics. If it is doing 
work, then it requires energy. It either must get that energy from the 
heat of the exhaust or from the motion of it. If it is getting it from the 
motion, then it resisting that motion aka back pressure.

It is clearly not getting energy from heat so it must be producing back 
pressure.

More accurately said, maybe is that a well designed turbo adds little to 
no back pressure over a stock or poorly designed exhaust pipe, because 
just having a pipe and muffler on the exhaust adds some back pressure.

Usually it is a bit of a tradeoff that works out to be a net gain...at 
certain speeds. So.. you loose a bit of power to the increased back 
pressure, but you gain a lot of power because of all the extra air - a net 
increase. It doesn't work at all speeds though, unless the turbo is able 
to adjust its back pressure across the whole range.

Turbos are a big win on things like ships or airplanes where the engine 
will be cruising for hours at a near fixed rpm. Then the turbo can be 
precisely tuned for that rpm and it doesn't much matter if it is a bit of 
a loss the rest of the time.


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