[Cliff R]

As far as timing curves go you must follow the rules above, NONE of the curve can be in at idle speed. The curve needs to start advancing right off idle and increase smooth and steady with the RPM's.

Since the vacuum advance is a load sensing device it operates independently of the mechanical curve. It will ALWAYS be adding timing based on vacuum. When engine load is light, vacuum is high so the VA is adding timing. Most VA cans don't start real early as far as the vacuum apply is concerned so no worry ever about them adding timing at heavy/full throttle and blowing up your engine. Using ported vacuum is exactly the same as manifold vacuum at light engine load and it goes falls off with heavy load despite what a few "experts" have posted on the subject on this and other Forum's in these discussions. The ONLY difference as mentioned before is that using manifold vacuum to the advance adds timing idle and coasting. IF you engine loves that deal then set it up that way. If it skips, miss-fires, bucks or kicks in protest reduce the travel of the VA and/or try not adding it at idle speed (ported source).

They make "adjustable" vacuum advance units by going thru the hole where the hose hooks up and turning an allen screw. Most of those you are only adjusting spring tension or when it comes in and all-in. Those VA units were meant more for tuners trying to get a LOT of timing in at idle speed in heavily cammed engine making really low vacuum to help with idle quality. They really aren't needed for tuning otherwise as all of these engines are going to make a LOT of timing in the "normal" driving range when engine load is light. Tuners can still play around with that deal some but I've never found anything there trying to improve fuel economy or anything else.

When I set up distributors here I look at the engine combo to come up with some numbers based on years of doing them. CID, compression ratio, cam, heads used, etc.

For most I'll shoot for about 10-12 degrees at idle, 9-10 degrees from the mechanical curve (18-20 at the crank), and another 10-15 from the VA.

For my last engine it didn't want, like, need or respond to a lot of timing anyplace. 455cid, 11.3 to 1 compression, 236/245/112 HR cam, ICL at 109.5 degrees, 200 lbs cranking pressure, 92-93 octane fuel.

It liked 10 degrees initial timing, another 10 from the VA and 10 from the mechanical (20 at the crank). I used medium/heavy springs on it, curve started at 900rpm's and all in at 3200. I used ported to the VA. If hooked up to manifold vacuum it didn't do much beyond developing a slight "skip" or "miss" in the idle note. So I left it on ported as it sounded better out the exhaust with very slight "lope" and still making 13.5" vacuum at 750rpm's and it barely fell off at all when the trans was placed in gear.

For the combo here I doubt if it needs a lot of initial timing. Probably 12 degrees or so, another 10 from the mechanical for 32 total, all in by 2800-3200 would be soon enough. I'd add 14-15 degrees vacuum advance and play with that some for best power in the "normal" driving range and fuel economy.

I'd add here that trying to track tune with the engine well over 200 degrees, hotter than balls outside, and slipping on the starting line isn't going to tell you much. In order to effectively track tune you need to have the engine at full operating temperature but not overheating, and good traction for every run. Otherwise you are only looking at MPH and even then it's going to vary a bit as nothing else is the same run to run. I'd go back to basics, take the timing back out of it and do some full throttle pulls in 2nd or 3rd gear and listen for detonation and at the same time makes sure it's pulling hard. It's always best to sneak up on those things, starting at 30 degrees, then 2 degrees at a time to see if it's helping our hurting. When you finally get to the track and can run cool, decent air and hook it, you'll be able to see your changes/improvements run to run and nail things down quickly...........Cliff