Deceleration valves.

[lowact]

Here is pic of the showing one of the deceleration valves at the front of ’86 HE V12 inlet manifolds. These are often discarded when such engine is used for an efi upgrade. If anyone has any such parts left over, pls can I buy?

[MarekH]

I have some, but they are in the loft, so ask me in about three months time.
kind regards
Marek

[lowact]

Thanks Marek. That will be round about my wife's birthday, easy to remember ...

[MarekH]

Just out of interest, why do you want them? You have mapped ignition and can tailor the fueling to every situation, including fuel cut during overrun.

The only scenario I can think of where they might be helpful is where you snap the throttle shut on deceleration and downshift coming into a roundabout. That'd perhaps give you a rich misfire as the fuel pressure cannot drop without fuel being used up to do it, but you can dial much of that out with negative acceleration enrichment. (Things like overrun fuel cut, retarding the ignition for engine braking and the like didn't feature on the 16CU which is when these valves were fitted. The 26CU and Denso v12s simply did away with them.)

If you simply want the housings as a handy vacuum feed for the pcv system, then that'd be more understandable.

kind regards
Marek

[lowact]

Mostly the latter, here is my thinking:

With my ecu (Haltech Nexus R5) I don’t need them (for fuel control), I suspect keeping them will potentially make overrun cutout control more complicated.

I have fitted an LdA overdrive unit. When decelerating (wheels driving the engine) these ODs are prevented from free-wheeling by the incorporated relatively puny friction drive mechanism. By retaining the deceleration valves I will be reducing the load on this OD deceleration drive mechanism which should prolong its life. Although this may not be essential considering that not a lot of heavy deceleration happens in 5th gear ...

I am going to try to re-engineer these valves to also be my idle air control valves (stepper motor type). I.e. to be dual function, active IACV’s as well as reactive deceleration valves.

I have duplicated the pcv outlets and will tee these into the hoses that connect from the air filter boxes to the deceleration valves. On HE engines the pcv was piped to both the inlet manifold (to be effective during idle) and to the air filter boxes (more effective at larger throttle openings). I am hoping that the above arrangement (pcv feed into the hose connecting to both the filter boxes and IACVs) will work just as well and be a much cleaner, simpler arrangement.

I also want to use matching deceleration valve (housings) to close off the rear of the inlet manifolds and for mounting my MAP sensors, one per bank (no balance pipe) ...