Manual boost controllers

[Robert Deis]

On Fri, 2 Feb 2001, Ken Keith wrote:

> > Nothing relieves the exhaust
> > flow to the tubo and boost builds very fast! 
> 
> I thought the boost in the exhaust manifold itself exerts pressure 
> on the actual wastegate, which can open it, even without boost 
> being applied to the bottom chamber of the diaphragm.

Depends on the spring strength.  Exhaust alone can't open it on my other
car- I expect the $$ is the same.

> > Now put an adjustable spring loaded ball bearing in the line to the
> > lower wg chamber, preset it so that it lifts off of its seat at say
> > 1.5bar, because the hose is small and short there is little volume.

This is the typical manual boost control setup.  Lots of companies have
put together their own version of this system for MBC and sell it for
anywhere between $40 and $150.

You can make your own for $8 in parts, but there are some tuning headaches
to work out, namely:

> The theory 
> was that boost pressure was getting "stuck" under the wastegate, 
> not allowing it to fully close.  When they added a check valve, it 
> fixed the problem.

The Hallman uses a (very) small hole to releive this pressure. I've been
experimenting along this line and found that the size of the hole is very
critical to the shape of the boost curve.  (Which makes sense, considering
it acts as a bleeder when the MBC valve is open.)

-- 
------------------------------------------------------------------------------
  Rob Deis                  "Let the people know beforehand what the law
  MiB3347                      is and what they are to expect." 
  rdeis at io.com                              -- 18th Congress, Rec. 75