Re: Supercharged vs. Turbo

[Brad Sheridan <brads@mindspring.com>]

At 12:52 PM 10/19/98 -0700, you wrote:
>Anyway, a chapter in the book is devoted to turbos and superchargers for VW
>engines up to 1989.  After reading this chapter, it was quite clear that he
>favored the supercharger to the turbo.  In fact, he states "Superchargers
>are inherently better then a turbo for a street-driven gasoline engine" (p.
>108).  The main advantage he pointed out for the supercharger was its
>ability to provide equal boost throughout the RPM range, as opposed to the
>turbo which has to rely on a wastegate system to provide this equalization
>(and hence is not as efficient).

The turbo is much more efficient, as it uses otherwise wasted energy to
provide the boost, while a supercharger drains power from the engine via
the crank. Displacement type chargers are quite inefficient, compared with
centrifugal type superchargers(basically half of a turbo, driven off the
crank). However with centrifugal chargers, you have to worry about the fact
that the engine operates over a broad rpm range, and it may be tough to get
a charger that will  work good across the whole range. It will most likely
either be spinning too slowly at low rpm to make boost, or spin too fast at
high rpm.

  There's also the issue of turbo lag
>(spin-up time), which is nonexistent for the charger. 

And for all practical purposes, nonexistant on the newer generations of
turbos, especially if it is well matched for the app.
 Note that the charger(unless designed with bypasses, something only coming
about recently) is on the boost all the time, which puts extra wear and
tear on engine components. 

 In fact, the only
>advantage he cites for the turbo is its ability to perform at high
>altitudes.



>Anyway, I realize this is one man's opinion (albeit an educated one it
>seems), and I'm sure there are plenty of turbo evangelists out there (on
>this list I'd imagine), but it does make me think.
>
>So let the debate begin!  What do the folks with turbos or are doing turbo
>conversions think?  Is it simply a matter of the parts for chargers not
>being available?  I'm also concerned about the longevity factor of a turbo.
>Superchargers seem to be more reliable, which is why VW chose to put a
>G-lader on the Corrado instead of a turbo (which they did experiment
>with)...

Superchargers are easier to plumb, I'll give them that.

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