Re: Turbo questions - K24, WG Spring etc.

[Orin Eman <orin@wolfenet.com>]

> Why stop with shimming the waste gate closed if that made more boost
> "sooner", i.e. at lower rpm?  Why not weld it shut.  Welding or shimming the
> waste gate doesn't "make" boost - all the waste gate does is allow you to
> control the boost once it's already there.  It does not make boost occur at
> lower rpms.  If you think about it, all a stiffer spring, or shimming does
> is prevent boost that's already there, in the system from being bled off at
> the waste gate.  And, if the shim or spring is set high enough, it will also
> prevent the ECU from doing its job of regulating boost as well.

A couple of things.  I agree that if you put enough shims in,
you may prevent the wastegate opening fully and interfere with
it's control of boost.  A little math and a ruler is all you
need to prevent this happening.

Secondly, the wastegate bleeds off _exhaust_, not boost.
As it opens, exhaust bypasses the turbo, the turbo doesn't
spin as fast and produces less boost.

As soon as the wastegate starts to open, some exhaust bypasses
the turbo.  If you move the point at which the wastegate starts
to open, that exhaust which would have bypassed the turbo
contributes to spinning the turbo and producing boost.
The earlier the wastegate starts to open, the less exhaust
is available to make boost and the slower the boost builds.

Therefore, more preload on the wastegate, either by using
a stiffer spring or shims will allow boost to build up faster and earlier.

It is very noticeable on my '86 5kcsq at freeway speeds.
The car was fairly mild mannered with the stock spring.
With stiffer WG springs, it will be building up boost on
slight inclines where it didn't with the stock spring.

Orin.