Advance vacuum

[Devito5692]

I'm looking to get a h&h ignition kit for my c20xe on weber 45s but I'm a bit confused with the advance vacuume they do a kit with vacuum and without so firstly what do I need to get and secondly what is the diffrence from having it or not
Hope someone can shead a bit light on this
Thanks

[meritlover]

zero vac+zero speed = base timing (hence why the tube is disconnected when setting the timing)
high vac+idle speed = slightly advanced timing to help the burn and compensate for poor cylinder filling
low vac+low RPM (accellerating)= returns timing closer to base timing. (better cylinder filling but low RPM)
low vac+high RPM (high load high speed)=bob weights increase advance above base timing.



it will make it more driveable particularly at low RPM/high to low loads. for example, pulling away and traffic driving. it would be a good idea to keep it.

[Devito5692]

Brilliant mate thanks so where do I connect the vacuum to?

[meritlover]

the manifold (any vacuum point between the valves and the butterflies)

[Adam]

It will run perfectly fine without the vacuum btw.
But as above if you do get a dizzy with vac advance

[skud52]

i run the h&h on a c20xe with r1 carbs, and dont have a vac advance, runs fine!

[meritlover]

running fine and running perfectly are 2 different things.
Of course it makes a difference to have a vac advance over just base timing and bob-weight advance.

to be fair. a lot of carb installs ive seen on novas and from forum posts where a random pair of 'fortys' and a manifold are thrown on and hopes for the best and remain hiddeously badly tuned or setup are certainly cars where you would never notice or desire a vac advance.

[mowgli]

ML, didn't the factory sport setup have a little valve in the vac line to lock the advance??

my 4 pen'th is that vacuum advance was invented for a reason, and a car will always run better with it in place. ok, if you are doing drag strip runs, where getting max power for a short time is the aim, it might not be needed, but for track & road, its a must.

[skud52]

im not 100% sure, and i havent tried it out yet, but i have been informed that the random black wire on the H&H ignition setup should connect to a throttle position sensor not to earth as i had it?? any input on this would be great as surely this is to simulate a similar effect???

[meritlover]

that must be like a primative 3d ign map. so it measure load against RPM and deliver the timing.
yes it will do a similar thing to a vac advance then.

[meritlover]

ML, didn't the factory sport setup have a little valve in the vac line to lock the advance??


they did, as did the early SRs especially the ones with the TIG camshaft.

i think it operated relative to engine temperature. i cant remember now.

[Jamie.bowen]

I run an XE on twin 45s with a mk2 cav dizzy... Sent my dizzy of to h+h to have it sorted so it would run with my carbs and cams and they blanked the vacuum of... Runs spot on

[meritlover]

I run an XE on twin 45s with a mk2 cav dizzy... Sent my dizzy of to h+h to have it sorted so it would run with my carbs and cams and they blanked the vacuum of... Runs spot on

did you try it with a vacuum advance?

[Jamie.bowen]

To be honest no I never tried just sent my dizzy of as advised to and that's how it came back

[Devito5692]

To be honest no I never tried just sent my dizzy of as advised to and that's how it came back

So it runs fine with out it. with low rpm ect?

[meritlover]

It depends what the point of the thread is and what you are willing to comprimise on.

For sure it will be 'fine' without the vac feature, and will probably be a cheaper option if you are trying to save money. But if you are asking what the best option is, i recommend a distributor with the vac advance.

[Jamie.bowen]

Ye all runs fine that's what h+h did to my dizzy they blanked it off to suit my engine