Here is the factory A12 spark curve

It is a Range due to manufacturing tolerance. And explains why measuring Total advance on YOUR car is important.

* You could be giving away HP if your distributor is on the low side (28) of the tolerance
* Your engine *might* be able to pick up more HP by going up to 33 or 34 degrees.

A12 factory curve

Yes, if the initial (static/base) timing is too far advanced, it will have very good low speed acceleration but won't rev over say 4000 rpm under a load. This is why a custom curve will help, get it advancing fast, but not too fast, and the engine will return additional HP at all RPMs.

Free additional HP.

Note that simply changing the base setting from 7 to say 14 degrees can have a detrimental effect at high speeds -- starting with pinging/knocking and ending with detonation (pre-ignition damage). It depends on various factors like grade of fuel used, and how much advance your engine can handle. Stock A12s are factory set to maximum 32 degrees total advance, which is a very safe setting. Setting it to 14 initial results in 35-39 degrees total (depending on your distributor's manufacturing tolerance) which is way to much. A14 might handle 36 well, but not the A12.

This comes into effect mostly at full throttle. At part-throttle, more advance can be handled by the engine. That is the purpose of vacuum advance, to advance the spark at part-throttle. And explains why racers don't use vacuum advance, as they don't compete at part-throttle.

Is there any rough limit to how far static advance can be though (just out of interest) before it may have a detrimental effect to engine at low speed? Probably no reason to set it too far advanced unless you're compensating for a malfunctioning mechanical advance mechanism or something, but would you anticipate any problems setting it a long way from spec? Perhaps all is good as long as it's not knocking anywhere in the rev range??

Static initial timing is least important to HP. The Total timing is most important.

First set total timing, then note where initial timing falls. That's your new initial timing.

Yeah mate, all good :) I guess I'm interested in knowing what static timing and total advance people are using. And what revs they are getting total advance at. Having said that, I should go and read the wiki entry for this first. I'm sure there's something there...

You understand that the stock A12 distributor does not have a performance curve. Even the emissions distributor has a better curve. Which mean pertronix will not increase HP, but it will be more reliable than points.

Total advance is most important, and is manually adjusted by rotating the distributor. Changing the weights for additional advance will make it take even longer to get to full advance. Heavier weights or lighter springs is the way to go to improve the curve.

Thanks for the threads. Informative as usual!

Thinking of just using a pertronix ignitor kit now for ease of purchase and installation. Preliminary investigation seems to suggest they're considerably cheaper to buy from the U.S but I'll look around.

Re: dizzy weights, I filed a little bit off my weights (where they hit the stop) to allow a few more degrees total advance after I read that a few more degrees total may be beneficial. It was years and years ago though (when I knew even less than I know now...so not much!) and I didn't give much thought to how it affected the progression of advance. Anyway, would be interested to see what curves people are using for different stages of engine tune.

recurving a dizzy gives some noticable gains i used a GM hei recurve kit in my points dizzy and it worked well... sort of

i tested the dizzy before the recurve it would get all timing in by very late around over 4000rpm think it was 4400rpm

i then took out the springs and put in the lightest (Gold) springs in both primary and secondary.

this gave quite a differnt feel of the line like more power but the springs are not light enough they fully advance at similar rates around 3900rpm.

the primary side advances significantly faster which gives better bottom end but it needs springs to be lighter for the secondary side so you can get it down to around 2000 or 2400rpm.

anyone got ideas were to get lighter springs or i heard you can weld on the weights to add some weight to it which speeds up the advance but i figured the blob of weld would interfere with the dizzy cam?

Recurve the distributor means to change:
* when the advance starts
* how much advance it can provide
* and when the advance reaches the limit

For more power, advance should build quickly, say fully advanced by 2400 RPM (but it may ping/detonate at that setting). Stock distributor are 4200 to 4800.

what is meant by the term recurve the dizzy?

Will be one of the best way to get rid of the old points system in my a12..