[Cliff R]

The way I tune all street set-ups here is to forget about the vacuum advance and find the ideal initial timing, then total timing the engine wants combined with the most ideal advance curve.

Once you find settings that allow for hot restarts without "bucking" the starter, and a curve that's fast enough for best power and total timing without detonation, lock the distributor down and forget it.

Then start adding in vacuum advance to improve things in the "normal" driving range.

Most very well thought out engine combinations will like about 10-14 additional degrees from the advance at cruise. This will improved off idle power, throttle response at low throttle angles, fuel economy, engine cooling and allow for a leaner mixture from the carburetor w/o negatives. This also adds up to less carbon build up in the cylinder heads and exhaust system.

With higher compression engines and relatively small camshafts you'll find 9 times out of ten ported vacuum to the advance will be the best choice. Same thing with very well thought out engine combinations making great power, there will seldom, if ever be any need to run the timing clear off the scale at idle speed to make them happy.

If you do not have an adjustable advance (for how much timing is added), there are several methods to modify them. I use the MIG here, but a screw and a washer can be made to work equally as well. Use drill bits to measure the travel of the arm so you know how much timing is being added with each modification. .120" is around 5 degrees (10 at the crankshaft).

You can also custom modify the mechanical curve in a similar manner with a positive stop for the advance. HEI's are slightly different that points distributors, but same basic concept, you need to control the amount of movement of the rotor from idle to full advance.

I attached a couple of pics showing how I set them up here. This gives you the amount of advance added, when it comes it can be verified and adjusted on the distributor machine or engine with a marked balancer and or dial back timing light.....Cliff

PS: those aftermarket advance kits are completely HOPELESS for attaining the same results, and are complete JUNK, IMHO. They move the relationship of the cam/weights and make it nearly impossible to establish a smooth advance without some of it in at idle. I just toss all that crap in the trash can when factory distributors show up here with it, and install the factory parts for perfect results every time.....