Seeking suggestions for small block advance curve
 

Well, the ongoing issues with the Mallory ignition system continue...the car is still not on the road. EVERYTHING except the distributor housing had to be replaced, distributor cap, "shutter wheel", electronic control module, ballast resistor, even the $100 coil...and I added a Mallory voltage spike protector to keep it from happening again. MUST have been some sort of catastrophic voltage surge.

Anyway, as long as I was into the distributor I thought I might customize the advance curve, so I am seeking suggestions for a curve for street use. I have never raced the car.

It has just the internal Mallory mechanical advance mechanism, no vacuum assist.

The kit from Mallory includes "spacers" (for lack of a better term) that will allow for adjustment of the total advance supplied by the distributor's advance mechanism, as well as a variety of springs that will adjust where the advance starts and the curve each supplies.

I would also like to know what kind of total advance figures people find helpful. I believe this to be a box-stock 5.0 HO long block from a '89 Mustang GT and modifications include an Edelbrock Performer manifold, an Edelbrock carb (575 CFM if I am not mistaken), the Mallory Unilite/ProMaster coil ignition system, and sidepipes. Like I said, it's not raced (yet), but I do like a spirited run to 90 now and then, so high-performance street use is the target. Total advance is adjustable by manipulation of initial advance and the total supplied by the adjustments the shims make possible. I do have a good Craftsman timing light, but it is not the newer variety that will display advance figures.

Thanks for whatever suggestions you can provide!

Cheers!

Dugly :cool:

Manipulating the timing curve for power requires dyno time, because the results are subtle.

Set base timing with a vacuum gauge. Adjust the timing where the vacuum is highest at idle rpm. Should be around 12-14*.

Total timing should about 36*, all in by 3,200 rpm's or so. That should work well for most combos. IIRC, the Mallory has a maximum advance of 28* in the mechanical advance.

The actual advance curve can be tricky. For power, you want it to come on fairly quickly, and then taper a bit so you don't get detonation as the cylinder pressure rises. But if it comes on too quick, and conditions are not ideal, you can detonate if you lug the engine a bit.

I'd start out with purple and gray springs, and see how that goes. Do your testing on a hot day.

Thank you, Bob...your advice is always spot-on! The shim that offers the greatest mechanical advance is indeed 28*. I have (had???) a vacuum gauge and will use it for setting initial advance at idle...should I look for the highest vacuum reading or the lowest?

If I ever take the car to a drag strip it will not be to race, but to do testing regarding various adjustments...accelerator pump shot, carb jetting. timing and distributor advance, that sort of thing...although I suspect that some dyno time with a good tech might well yield more reliable results.

Again...thanks for all the help you have given me, not only on this issue but others, too. It is appreciated much more than you can imagine!!!

Cheers!

Dugly :cool:

Set it where you get the highest vacuum reading at idle. As the timing and vacuum changes, so does idle speed. So you just have to keep adjusting both at the same time until you get it right.

If you don't have a vacuum gauge, you can use a bowl of water. Set it on the cowl, and adjust the base timing and idle until the ripples in the water are the smoothest.

Dyno time with a good tuner will get the most accurate results with the least amount of effort. But if you know what you're doing, you can get good results with street and strip tuning.

Thanks! I will either find my vacuum gauge or buy a new one. It is a necessary tool, IMHO...I even remember when a vacuum gauge was standard equipment in the dashboard on some cars...most often marked "Economy".

Onward!...through the fog :eek:

Cheers!

Dugly :cool: