[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: Compressor bypass vs Decel
In a message dated 97-10-20 00:05:11 EDT, you write:
<< Just a quick thought, does the deceleration valve open
>during shifting? Or does it respond too slowly? If the
>decel valve does open during shifting, could it cause a
> lean condition (lag) when the airflow plate drops and then
> has to come back up?
No, not really. The DECEL solenoid only kicks during idle switch activation
(computer controlled electric solenoid), which we all know to be full closed
down to ~1100-1400rpm, when idle circuit takes over, and decel solenoid power
deactivated. So the cars with the delay shut won't have this problem, those
going only partly closed won't either. Given this, really all the decel
valve is doing is preventing the rich fuel spike by slam shut throttle,
dumping Pv on top of the flap to Po below it. By the time Pv is back, the
flap will kick up pretty quickly. If one takes the flap to full up then lets
it fall it would take about 1.5 seconds to drop to full rest. So if one is
speed shifting or performance driving, doubt the flap is at full rest anyhow.
Remember the flap is dropping with gravity, raising with vacuum. So the
drop will take longer with the decel valve actuated than the rise with
vacuum. Hooking up a A/F meter confirms that by the time you are back on
WOT, so is the fuel.
>Just wondering......what the hell does that CIS airflow
>plate do... during all this commotion........
And here starts the nerdy part of keeping bypassed air closed loop. If one
pops to atmosphere, you will raise the flap slightly as the valve bleeds off,
cuz the freewheeling turbo is not considered freewheeling by the CIS flap, it
considers freewheeling turbos as the same vacuum as WOT, until the decel
valve is actuated. The decel only opens on Idle switch activation, the
Bypass valve needs only Manifold vacuum for dump. Bypass Valve operation
DOESN'T have to be a fully closed throttle, only vacuum in the intake
manifold. Rich fuel spike, hello. O2, CAT, and flames don't mix well.
Theoretically and practically, you could drive a whole track session never
actuating the Decel Valve. Claiming that with the Bypass Valve would
indicate a very straight track (read: impossible)