[DML] Re: Turbo PRV.

["David Teitelbaum" <jtrealty@xxxxxxxxxxx>]

I do not claim to be an "expert" on turbos. My main point in saying
there should be some kind of pressure release valve is that if a boost
control should get stuck or a wastegate not move right you could
overboost the engine. Having some kind of valve seems to me to be
insurance against something going wrong. Single point type of failure
kind of thing. With some of the Island turbo cars blowing pressure out
the crankcase either some of them have the boost set too high or there
is some kind of transient condition that is allowing the engines to be
overboosted. We can argue over exactly what kind of valve to use and
where to put it but IMHO adding a relief valve won't do any harm and
can protect the engine from an overboost condition. BTW the poppet
valves (decel valves) allow air to pass the throttle plates under high
vacuum conditions (higher than idle). Refer to D:09:01 for a more
complete explanation. Maybe for the turbo installation they need to be
modified? They aren't needed on an automatic, they are mainly for a
5-speed so additional air can go through the motor to prevent
backfires in the exhaust.
David Teitelbaum
vin 10757


--- In dmcnews@xxxxxxxxxxxxxxx, Martin Gutkowski <martin@xxxx> wrote:
> 
> David Teitelbaum wrote:
> 
> >
> >I have to admit I never actually measured this. It could be that it
> >isn't that big a problem on a Delorean since the turbos are rather
> >small and would respond quickly. It is still possible though. There
> >are decel poppet valves on the throttle plates that allow air to pass
> >even with the throttle plates closed. 
> >
> I haven't looked lately but I thought these were safety valves that 
> operated in the opposite direction to allow the engine to backfire 
> without destroying the throttles. On the Renault engines, where the 
> brass bypass screws are used, the throttles don't have these valves.
> 
> >In any case a blow-off valve
> >(recirc or not) could only be a further safety item especially if
> >something happened to the boost control or wastegate. 
> >
> Er, no, because they only do anything when the throttles are closed and 
> there's a vacuum in the intake manifold. On the Island and BAE kits,
the 
> whole turbo is in a vacuum so a dump valve will do precisely nothing 
> except maybe give a big vacuum leak.
> 
> > I do
> >not like the recirculating type, they can increase the temperature of
> >the incoming air charge, better to just dump it. I think the recirc is
> >used because it is quieter. 
> >
> Possibly, but on any air-mass metered engine they are a must otherwise 
> when you throttle back and the dump valve goes, it'll meter a load of 
> air that's not actually going into the engine - consequence, soak the 
> bores in fuel. On the legend engine, where the (effective) air mass 
> meter is downstream of the turbo, the dump valve would have to be
before 
> the sensor plate, for exactly this reason. The ideal place for the 
> turbos to be on the stock DeLorean engine would be between the sensor 
> plate and the throttles. but this is hardly practical!
> 
> Martin








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