Re: Turbo Performance upgrades

[Brad Sheridan <brads@mindspring.com>]

At 02:25 AM 9/2/98 -0400, you wrote:
>    I was thinking about changing the throttle body on my car either to a
larger
>later model unit or to a weber big single I have lying around. Do you
think this
>is a good idea? I ask only because I am new to the turbo thing and I
wonder if
>all the same sort of rules apply.

A throttle body should help out. I would not recommend a Weber, as they
have a smaller cross section than the later style A2, or Audi TBs, and they
are not a dual butterfly design. The single butterfly designs have much
more of an on/off throttle response, which will probably make the turbo
much less friendly at anything less than full throttle. The Audi, A2, both
have two seperate valves inside, the primary is smaller, and is what is
mainly opened up for light throttle, resulting in good part throttle
control. Then when you hit the throttle hard, you quickly open up the
secondary for more flow.

> Are there any "upgrades" that don't really
>work well with the turbo?

Long headers. You don't want too much piping between the engine and
turbine, this would allow the gas to cool, and possibly slow down some.
High compressions pistons, shaving the head, and other things to increase
the compression generally aren't good.

>Is it true that the larger the exhaust is, the better?

Yes. But if you're running a 3" exhaust, you won't get much if any gains
from going bigger. Depending on how much power you have, 2.5 to 3" should
be quite adequate. For the base Callaway kit, producing less than 150hp, I
think, the 2.5 is plenty. Before bothering with this, consider fuel
enrichment, intercooling, and getting an upgraded turbo. Also, if you don't
have them, gauges to monitor engine vitals, and a turbo timer to run idle
the car and help the turbo cool down after use.

Brad

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