Re: Compressor Bypass Valve

[RayVR4@aol.com]

>It is awfully small and, yes, it is 35 bucks for a cheap little plastic
valve.
>Is this valve actually big enough?  Does the turbo not need much flow
capacity
>when it is recirculating?  I am going to look at an HKS (~$50.00-$100.00) or
>Trust piece, since they are larger diameter, and they also have a "vacuum"
port
>on the bottom side of the diaphraghm that can be plumbed ahead of the
throttle.
>This short burst of high pressure helps to flip the valve quickly.
> Would an electric solenoid actuated valve be better?  You could trigger
>it with a closed-throttle switch.  It would be very fast!

Any type of compressor bypass valve is going to be better than none at all.
 Beyond that, the larger the valve, the less back pressure the compressor
wheel will "see", the better the turbo will maintain shaft speed and the less
backpressure you'll get between the turbine wheel and engine.  One comment
that Turbo & Hi-Tech Performance had when testing an S4 was that the
compressor bypass valve was large enough that there was no noticeable hiss
when it opened so it's probably "large" enough for stock boost.  My Galant
with a similar sized valve has a very noticeable hiss (sounds like a truck
releasing its brakes) when the valve opens at WOT @16psi of boost.  If you
wanted to really do some testing you could hook up a sensitive boost gauge
between the turbo and throttle to see if there's any pressure imposed by a
restrictive valve (you can do something similar on the filter-turbo side to
see if the filter is being restrictive and creating a vacuum).  As far as the
speed of the valve opening and closing we're now talking about fractions of a
second which may or may not make a difference depending on what you're doing
with the car <grin>.  For $35 bucks it may be more economical to put two
valves on rather than one expensive one.  It shouldn't make a difference
where the bypass valve is tapped into the turbo-throttle side plumbing so it
probably makes sense to put it on that side wherever it's closest to the air
sensor-turbo side plumbing to keep the connecting pipe short..

On a side note, if you didn't channel the bypass air back into the air
sensor-turbo side you'll effectively have a blow off valve and since the
engine computer thinks that all air flowing through the air sensor is being
used by the engine, you're going to end up with an overly rich condition when
the throttle is closed during boost.  I think this is what causes flames to
shoot out the exhaust of race cars when they shift (probably not good for
catalytic converters).

Ray