vacuum advance or not - Griff 4.0

[kabaman]

Recently I've done various bits of work to the Griff. One of the things I replaced was a knackered vac advance unit. I believe this is responsible for my cooler idling (car used to get very very hot when stationary). There's a slight sort of mis-firing on over-run or very partial throttle. Car is fine whilst accelerating (even slowly) but once speed is static with throttle a small way open the enine is not entirely happy. I'm experimenting with changes of timing and I haven't formed an opinion yet but I'm starting to think that maybe the vac advance is advancing too much. Too early to tell yet.

Anyone else out there with a Griff 4.0 run a vac advance?

Any comments that might save me some time would be appreciated.

Thanks,

Neil

[350Matt]

Hello Neil

Definitly run the vac advance but and important note is to set the ignition timing at idle (8-10°BTDC) with it disconnected and use a decent timing light

[Barreti]

As part of my whole 'i need to understand ignition' I could do with understanding this too, so please excuse the thread going a bit O/T Kabaman

My vac advance has a black pipe off it which plugs onto a fitting poking up out of the inlet of the plenum. It also has what looks like a little see through fuel filter about half way and I'm curious about that.

two questions
a) Should the tube on the plenum be clamped somehow. Mine isn't.
b) To my mind, a filter would impede the correct use of the vac advance so is what I'm looking at not a filter or does the advance not mind it being there?

Mine's a 4.3 Kabaman so my questions may help too.

Edited by Barreti on Wednesday 17th June 13:31

[rigga]

Its not a filter in the pipework,but a one way valve to stop fuel vapours traveling down the pipe to the vac unit and destroying the diaphram.... a push fit by the pipe onto the plenum is fine,no need to clamp the pipe at either end,should be a snug fit though obviously....

[Barreti]

Cheers Rigga
Kabaman can have his thread back again now

[RichB]

Interesting, it was me that commented that my 500 doesn't have one and that Mark Adams, V8 guru had said not to worry so did the 4.x cars have them and the 500's not? Or is it something Mark does with his Tornado chip that means it's redundant? I've got ACT Plenum and Mark's Tornado ECU.

[David Beer]

my 500 came with it but i always ran without it, less shunting. When i had the twin plenum, you have no choice as there is no take off.

[v8 racing]

To clear a few things up here, vac advance is good for fuel consuption on reltively standard engines (range rover engines) a 500 or any engine with cams above 280 deg duration and ported cylinder heads will run smoother with less shunting without it connected, the main reason being airspeed through the engine, the vac advance pipe basically gives more torque (power) to the engine at light light throttle positions, so not much air is passing through, by disconnecting it to do say 70mph down the road you will need more throttle opening and hence more air speed which means a better combustion, the reality is for the sake of a pipe try and see, personally apart from stock 400's and 450's i never connect them

[kabaman]

"shunting" I think that's what I'm experiencing - sort of slight missing that makes car jerky at low revs. Is that what's meant by shunting?

Cheers,

Neil

[rigga]

My 500 runs better with a working vac advance unit...