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Re: popoff valves

Quite a bit of editing.  Linus, the way I understand it is that the 
pop-off valve would be in the same location as what you're calling the 
turbo bypass valve.  Only, instead of relieving excess pressure back to 
the inlet to the compressor, it simply vents it into the air.  So the 
path would be:
	Air filter (maybe some CIS sensors at this point?)
	Return from Bypass Valve (if present)
	Turbo compressor inlet
	Turbo compressor outlet
	Either Pop-off valve or Turbo Bypass Valve
	Throttle body
	Intake manifold
	Intake ports
	Exhaust ports
	Turbo Wastegate (to air or downstream of the turbine exit)
	Turbo turbine inlet
	Turbo turbine exit
	Turbo Wastegate return (if not dumped to air)
	Big huge 3 1/2 straight pipe back to a Dynomax Glasspack - Yeah!!!


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

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

> 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.  
> but that closed throttle would lead to two more problems--1) big pressure
> spike between the throttle plates and the compressor (typically leading to
> blown intercoolers) and 2) big time drag on the compressor.  this is where
> the turbo bypass valve comes into play.  The bypass valve DOES vent excess
> pressure, but instead of from the intake manifold, from the chamber between
> the throttle plates and the compressor--on high manifold vacuum (closed
> throttle) the valve opens, allowing pressure to vent from between the
> throttle plate and compressor, 1) minimizing the pressure spike and 2)
> feeding the vented pressure back to the intake side of the compressor,
> helping keep the turbo spooled up.  At least this is how I see it set up on

> --ldt
> ----------------------------------------------------------------------
> * 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'    *
> ----------------------------------------------------------------------