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« on: June 10, 2013, 04:18:00 PM »
I have a 68 L30 327 4-speed car. It originally had the AIR system on it, but the entire system was removed shortly after delivery. It has the original distributor and the vacuum advance is hooked up to ported vacuum. The car has always seemed to run well. Original static timing spec for this car is 0 degrees (IIRC). So at idle the timing is at TDC (0 initial + 0 vacuum adv + 0 mech advance)
Based on my research, I want to change the vacuum advance to connect to full manifold vacuum, and play with the springs on the mechanical (centrifugal) advance to start advancing just over idle and be "all in" by around 2800 rpm. Research also indicates that I want my initial static timing at about 10 degrees, with max mechanical advance limited to about 20 degrees (rough numbers). My issue is that my mechanical advance plate allows for 34 degrees of crankshaft advance (17 degrees distributor advance). I measured this on the mechanism, and it corresponds to the stamping of "734" on the part, the last 2 numerals indicating total crank advance. The original bushing is in place on the mech advance limiting pin, and the mechanism operates smoothly. With 34 degrees of mechanical advance, I will still need to keep my initial static timing at about 0 degrees so that my high rpm low load cruising timing isn't excessive ( cruise timing = 0 initial + 16 vacuum advance + 34 mech advance = 50 degrees).
My plan is to:
1) Install a vacuum advance canister that will provide 16 degrees crank advance at idle vacuum conditions (connected to full manifold vacuum).
2) Change the mechanical advance springs to start advancing just over idle and be "all in" by around 2800-3000 rpm.
3) Keep initial static timing at 0 degrees.
4) Keep existing mechanical advance limit arrangement at 34 degrees (I really don't want to modify the limiting slot).
Is this a good plan? I know my timing curve will still not be ideal, but this should be a step in the right direction, correct? Any other comments or suggestions? This isn't a race car, but I'd like it to perform well.
Thanks,
Jeff