DansYellow66

You may remember my recent post - Anyone running BB 3946074 aluminum heads? Anyway I got my VC1810 vacuum can limited to 6 degrees crankshaft advance and that cured the over-advanced "missing" at cruise speed. Six degrees doesn't sound like much but it does boost my idle timing from 13 to 19 degrees which helps idle and cold start up considerably. Cruises clean now at highway speed.

In checking my timing to see what I ended up with after limiting the vacuum advance, I realized that I was getting into the centrifugal advance at idle (800 rpm). A number of years ago I put what I believe was a Mr. Gasket MG 207 kit in the 67 427/400 mag pulse distributor that I'm running. It had replacement advance weights, bushing and springs and I've been running the lightest springs.

From memory I think I have 20 crankshaft centrifugal advance in the distributor now (28 was supposedly stock) but I need to double check it as it's been awhile, and that seems like a lot for a bushing to take out of the distributor alone.

I scrounged up what I believe are the springs that were in the distributor when I acquired it and they are a little stiffer and hold off centrifugal advance at idle. However, as soon as I touch the throttle it starts advancing - probably by about 850 rpm or a little more. I ran out of time before I could play more with it and see at what rpm full advance now comes in at. I was hoping I could hold the mechanical advance off a little longer to try and improve the first gear low-speed-surging at light-throttle I sometimes get.

Question is - those of you who have tuned your distributor advance curves, what rpm do you have the centrifugal starting to come in? As long as it's all in by around 3000 rpm should I just call it good?

Thanks

Dan

67-427ci

Dan: This how my curve looks. It was curved by LARS and starts at 900 RPM and is all in by 2,700 RPM and the vacuum advance provides another 16 degrees advance. My engine is a zz454/440hp with aluminum heads.
Roy

BarryK

Dan

on my '65 L76, the idle speed is between 850-900rpm. Centrifugal advance doesn't start to kick in until about 1050-1100rpm. it's all in by 2900-3000rpm.
That's actually a longer curve than factory - factory was all in by about 2450rpm on that set-up but with today's fuel compared to the fuel in the 60's I figured it was a safer set-up.

DansYellow66

It sounds like I'm going to be in the ballpark with what I have.

Thanks

Dan

BarryK

you do want to pull any centrifugal advance coming in at idle out. You don't want it to come in until about 200rpm's or so above idle speed.

play around with different springs - just so you get no centrifugal advance in at idle yet it still brings the total timing all in by 3000rpm or so. If you are currently running the lightest springs for both, try going up to a medium spring on just one and see what happens. both springs don't need to be the same, they can be mixed - whatever it takes to get the advance to come in when you want it