RE: BYPASS valves...

[QSHIPQ@aol.com]

Are what they are, a blow off valve, is a maximum boost popping device that 
activates at a predetermined boost level (say 30psi boost) to prevent the 
engine and turbo from blowing up, blowing all boost pressure out of the 
system.

A bypass valve (or a couple of them) is to keep the turbo freewheeling during 
sudden closed throttle (on boost) operation.  What you might forget on closed 
throttle with all 86> turbo CIS/E/III cars is that there is what's called a 
decel valve that would prevent any fuel spike as the bypass valve actuates.  
What the decel valve does, is open the loop between the air boot (vacuum 
opening the fuel flap) and the post air filter box (pre fuel flap), 
effectively equalizing pressure, eliminating the fuel pressure spike caused 
by either turbo spool up with no bypass valve/s, or turbo freewheeling with 
bypass valve/s.  

Be advised too, that the feeding of k26/RS2/K24 boosted air back into the 
intake side of the turbo, adds little in terms of pressure (or in CIS case, 
increased vacuum on the top of the flap) to the system.  The theory is that 
metered air should stay closed loop, that's all.   With a decel valve in CIS, 
there is no fuel spike, with either bypass valve/s installed or not.

HTH

Scott Justusson
QSHIPQ@aol.com
'87 5ktqwRS2 -10vt
'84 RS2URQ - 20vt
'87 4Runner turbo