Recurving my advance.

[oldpurple]

I understand the theory behind most of this, but It is something I haven't done on my own and I'm not exactly sure what I'm aiming for. I'm wondering if anyone has advice on roughly how I should be changing the advance curve.

Engine: Stock 1979 350 with ~60k miles, Edelbrock 2102 cam specs here, Old style Edelbrock performer intake, long tube headers, TH350 w/ stock converter, 3.07:1 gears.

I have the initial advance set at 14 degrees as per cam instructions. I have checked the mechanical advance and it adds 22 degrees @ 3400rpm. My vacuum advance adds 15 degrees.

I understand I want the advance in earlier than 3400, but how do I know when and how much? I realize every engine will be different but It'd be nice to have a bit of an idea of where I should be going with it.

Any help is appreciated.

[WorkinLonghorn]

Well, I'm sure others will come along that have tons of experience but I'll tell you how I did it on mine. I bought an adjustable vacuum advance and with it came some different springs in pairs with different color codes. There was an instruction manual on exactly how to curve a distrib.
I just followed those instructions. You make some full throttle passes and change the springs if needed. I think there was instructions on limiting the total advance if needed with a little sleeve or something.Then adjust the vac advance for most economical cruising just short of knocking. -BA

[geezer#99]

Actually 36 degrees all in at 3400 isn't too bad.
At elevation like yours your motor might like a little more initial. You'll need to experiment to find that number. Just bump it up 2 degrees at a time until it pings or is hard to start hot. THat will be your best initial. Then modify your distributor to give you about 32 degrees total at 3000 rpm.
Look here for some info on that.
http://www.crankshaftcoalition.com/w...EI_distributor

[Wrenchbender Ret]

To bring the advance in earlier you just need to put lighter springs on the advance mech. The vacuum depends on what vacuum it takes to pull it on. With a mild cam like that it should start at about 5-7 in. & all in about 12. Rest of it seems to be good to me. You don't want more then 36 total (without vacuum). If it runs rough in neutral about 2000 to 2500 rpm you have too much total advance. You will need to limit the vacuum advance amount. Every engine it different so you need to experamint with yours till you get it good.

[PGSigns]

This is from another thread and covers most of the process.

Here is a couple of thoughts on timing. You really cant ad total mechanical advance and total vacuum advance together and get a number that is really achievable. Here is what you do. Pick a total advance that you want for wide open throttle like 36 degrees to start (it may want a bit more but its hard to tell) then pic what you need at idle and when you need the timing all in. So for this example we will pick 36 total, 14 initial and all in at 3000. So with an adjustable timing light or a timing tape do a test of just you mechanical timing and see what you have and then make adjustments with weights and springs to get you the amount of total you want and at the right time. Then take it for a run and see if you get any pinging or if it seems to want a bit more total timing. Once you are happy with that part then ad the vacuum back to the system. Vacuum pots are rated for when the start to work and how much advance they ad. I run ones adding about 12 degrees. I run mine off manifold vacuum. What this does is ad timing at cruise and other high manifold vacuum areas to improve idle quality and cruise fuel economy. It also will pull that extra timing out when you have a heavy load or you mash the gas to prevent the added timing from causing detonation. Now do another test drive with the vacuum hooked up and see how it runs. If you have a little detonation when you roll in the throttle you need a pot that requires a bit more vacuum to pull it in. This drops out the extra timing a little sooner when your manifold vacuum drops under acceleration. So you can see how the two work together but never really ad up to the two total numbers when running.
Jimmy