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Re: Popped

Jeremy, et al,
>Is there such a thing as TOO MUCH pressure at the INTAKE MANIFOLD?


>I guess I'm showing (and simultaneously trying to remedy) my ignorance on
>turbos.  But what could happen with tons of pressure at the manifold
>(figurative tons, that is.  Not literal ones)?  Will the intake manifold
>blow off of the head?  I can't imagine the head gasket blowing from
>intake manifold pressure?

That's the weak link, as chipped 944 turbo owners can probably attest too.

> Will that cause too much mass to enter the
>cylinder and blow the head gasket on the piston compression stroke?
>Plus, the compressor won't compress too much unless the turbine is
>receiving too much energy from the exhaust.  It's a direct mechanical
>correlation.  And the prevention of this occurence is the sole task of
>the wastegate, is it not?  So why (Linus) would you need a valve to bleed
>pressure from the INTAKE manifold AFTER the throttle body?

I think this thread started when someone mentioned  a description
of Al Swakhammers(sp?) 4000 quattro which he turbocharged maybe
10 years ago, and they said he installed a pop-off valve to control boost
pressure. Some background. The first version(and maybe others) of the
engine didn't have a wastgate. In place of a wastegate, Al installed
a pop-off valve on the intake manifold to control the boost. So the
turbo would just spin up and when the intake boost pressure
exceeded the control pressure(probably a spring) of the
pop-off valve, it would vent to atmosphere.

If I am not mistaken, indy cars used a pop-off valve on the intake
manifold as their sole means of boost control. In years past,
CART would keep all the valves and distribute them to the teams
before a race. All the valves are set to have the same max boost
pressure. They all have tamper resistant hardware, so if a team
decided to alter the pop-off valve max boost setting, the authorities
would know.

>The only
>reason you need a pop-off valve (which is located after the compressor
>and before the throttle body) is to give the air coming out of the
>compressor and "bouncing" off the closed throttle plate a place to go so
>it doesn't blow up an intercooler or stop the turbo.  Is this logic
>false?  Scott...Glen?

That's the function of the turbo bypass valve, which has been sufficiently
described in earlier notes. You can either dump the extra boost to
atmosphere or re-route it to the compressor inlet.
Dave Lawson