Blow-off valve control

[Rodney_L_Wiggins at keybank.com]

This is a very common problem when trying to vent a factory bypass valve to the
atmosphere.  You have two options. The first, is to convert to speed density
enginge control so that the engine management system doesn't care what is
happening to the air (false or otherwise) ahead of the throttle plate.  The
simpler and more economical option is to use an aftermarket blow-off valve.  The
advantage of the aftermarket valve is the adjuatability of the spring pressure.
Diaphragm or piston are fine as long as you can fine-tune the spring tension.
The idea here is to increase the amount of vacuum required to open the valve.
On the stock valves engine vacuum at idle is sufficient to open the valve
slightly.    Of course when the throttle is snapped shut at 3000+rpm vacuum
levels are much higher, and you have positive pressure on the plumbing side of
the valve, this is when you want that valve to open.  Still, you will spend a
fair amount of time dialing the valve in to minimize drivability issues and
maximize compressor bypass.  (But the cool sound is well worth it)  Too little
tension, and the engine will stall when you close the throttle in no boost
situations.  To much tension and you will not relieve boost pressure when you
need to, resulting in compressor stall.
Hope this helps,
Rod Wiggins
86 944 turbo, nitrous, big turbo, etc.
69 Land Rover. blindingly slow, but very capable.


----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org