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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
>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
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.