can anyone time tell me how much advance the vacuum advance diaphram gives? How abouit the mechanical advance ? I may have to recurve the dizzt , of lock the weights to stop my supercharged motor pinging.

Depends on the dissy but typically 14 -16 degrees of vacuum and 10 degrees of centrifugal advance.

I have already unhooked the vac advance, do you think it would cost me power to lock up the mechanical advance? Whenever I open the secondary It rattles like a bastard.

Vac advance only works at partial throttle like when cruising. The lighter the throttle the more advance.
Mechanical advance is engine speed dependent.

If you are getting problems at full throttle check timing and things like air leaks or coked up combustion chambers.

There has to be a reason for the "rattling" and if the timing is set correctly its usually a mixture problem.

Hi Bart
My understanding of vacuum advance is that is really an economy device and has little effect on performance (when there is no vacuum). The A series Nismo race distributor has no vacuum advance so I'd disconnect yours.
My diagnosis is the rattle is caused by to high a cr or too much static advance.
Good luck
Jon

The compression ratio of my engine is 7.9:1, so I doubt that it is too high. (although I am making 11+psi at full throttle) I'll try retarding it some more . Maybe feral is right, Perhaps my secondary jet is too small. However, it wouldn't be untill both holes are wide open that the blower can make full boost. Thre is very little chance that the chambers are coked up as I have had the motor to bits before I started.

I think KB110 may be on the right track with the comp ratio thing. I didnt notice this was on your supercharged engine.

With 7.9:1 and 11 pound boost, the equivalent comp ratio is 13.8 to 1, so timing would be critical. For this amount of boost you should have a total advance of about 22 degrees. Get a cordia turbo boost retard canister fitted so it retards under boost.

A lean mixture wouldnt help the problem. Get an air/fuel mixture probe into it while under load. Then see how the mixture is.

How can I set ( or limit) my total advance???
I might have to pay someone to set it up,but I am too mean to pay the prices that the pros charge.(and sometimes the socalled pros are just monkeys,who love to charge like wounded bulls. A mate of mine got stung $1500 just to fit a fourbarrel manifold and carb, which he supplied! (brand new) and they conveted his remote oil filter to mount on the inner guard. $1500!!!!!!!!!!!!

If any one wants to know who that was pm me and I'll tell you where NOT to go.
Oh yeah, and when he came to pick it up they had got the hoses around the wrong way, and when he started it it rattled like a bastard. because of the anti drainback valve in the filter block. (no oil pressue) And when they rebuilt the mtor for him before that , they stung him for $3000, which was suposed to include cracktesting. When we got it going water was squirting out a crack in the head!!!!! This guy is suposed to be one of Christchurch's resected race motor builders!!!

You could try a spot of solder on the weight stops, this will knock back your total mecanical advance. Or take your dizzy to the Polytech and see Mr Haliwell who I am sure would be only too happy to spin it up on his graphing machine. Barry Emms of quality rebuilds also has a graphing machine if thats any help.

Quote:No way! It helps part-throttle performance. Why would you want to run with retarded timing? You want as much timing as possible without pinging. Vacuum advance doesn't work at idle, so it won't make the car hard to start.

Quote:When there is no vacuum means full wide-open throttle. True, extra advance is not needed in this condition. If you drive mostly at WOT (like a drag racing car for example), you won't benefit from vacuum advance. In this case, make you setup simpler and disconnect the vacuum advance.

For a turbo car, if you ever drive with no boost (low rpms, whatever), it might still be beneficial. But using a combo advance/retard module is probably better than disconnecting it.