Re: Popped

[Jeremy R King <kingjer@eng.auburn.edu>]

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?  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?  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?

Jeremy
'86 VW Quantum GL5
Auburn University, Alabama, USA
Hometown - Reidville, South Carolina, USA

On Wed, 28 Feb 1996, linus d. toy wrote:

> At 08:00 AM 02.28.96 -0500, PDQSHIP@aol.com wrote:
> >In a message dated 96-02-28 04:51:40 EST, you write:
> >>
> >>I've always thought of a pop-off valve as a pressure-relief valve that opens
> >>if manifold pressure rises to a certain point--which means it operates on an
> >>OPEN throttle and only if it's relief point is reached.  A closed throttle
> >>would quickly drop manifold pressure and keep the PO valve closed.  
> >>
> >That is the wastegates job...  A pop off valve or bypass valve are the same
> >thing....  the pop off valve can be routed to the intake side of the turbo or
> 
> I realize i didn't make that very clear--i should have said that the pop-off
> valve is mounted to the INTAKE manifold (in contrast to the WG on the
> exhaust side) PAST the throttle plates.  in this position, if you are
> stubborn and keep your foot into it beyond sanity (i.e. safety for the
> engine), the PO valve does control boost level.
> 
> >to atmosphere, it's function is the same AT CLOSED THROTTLE, to 1) let the
> >turbo freewheel and 2) to prevent pressure spikes at the IC.....  Venting it
> >to atmosphere is the easiest and usual racers way of installing the valve
> >(big farts), the return to intake of turbo is the more quiet and sane method
> >used by most production cars.....  The same valve can be used for either set
> >up.....   BTW, most atmosphere pop off's I've seen have a K&N filter attached
> >to them to prevent oil blow and the possibility of sucking crap in the hose
> >during transition....
> 
> i see now what you're referring to as a PO valve and bypass being the
> same--it would be the same kind of a valve but mounted BEFORE the throttle
> plates.  again, this is the second function we've been discussing, the
> closed throttle situation, especially for when it's snapped shut.
> 
> --linus
> ----------------------------------------------------------------------
> * linus toy           email:  linust@interramp.com                   *
> *                                                                    *
> * "...it's stuff that does things people want, but they don't know   *
> *     how it works.  But if they did look inside it would probably   *
> *     have lots of wires."                                           *
> *                            --4 year old explaining 'technology'    *
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