Discussion Forum - Northstar Chevelle Club

You don't need such a wide timing curve.  Here is how I would set it up.

Figure out the timing that makes the best HP or MPH at the track. Be it 34, 36, 37, whatever.  That will be max setting (all in) without vacuum advance. 

I would limit the mechanical advance to around 15 degrees with it fully advanced by a couple hundred RPM's below what you cruise at, so probably all in by 2500.  Most adjustable kits have a max advance stop or some kind of limit screw so you can adjust that.  You will need to use whatever springs the curve needs to get it all in by 2500. 

This needs to all be done with the vacuum advance unhooked. 

You want the total advance under low load with the vacuum advance connected to manifold vacuum to be in the 50 degrees BTDC area, maybe a bit less. (this is under steady low load driving conditions) This will vary depending on where your engine likes the WOT timing.  An adjustable vacuum canister is nice to dial it in better.
 
To give you an example, with the vacuum unhooked, my car is set at 37 deg total advance, all in at 2500 RPMs.  My vacuum advance adds 10 degrees and is off at 4" of vacuum. I use a 15 degree mechanical curve, so at 1000 RPM's my timing idling is 32 degrees.  37-15+10.    At 2500 RPM driving, I am at 47 deg advance under low load.

Once it's set up, then cruise around, checking for detonation at different throttle inputs and loads.  If you aren't getting any and the car seems responsive, you are good to go.    

The only thing that has an effect on your quarter mile is the total timing  and whether or not the advance is all in soon enough.  Vacuum advance has nothing to do with it as it doesn't work under load.