Hey guys I just started playing with my Nailhead distributor. It's a stock 55 unit going into my 55 special 264 with dynaflow. I found that my car loves 15° of initial timing, it practically jumps when you touch the throttle. However it will run hot once you get it moving. The exhaust is loud so Im not too sure if there is any pinging. I have a spare distributor and i want to try and recurve it. I set up my Alen distributor machine machine with the junkyard distributor and I have about 15° of mechanical timing in it at close to 4000 to 4500 RPMs. I'm going to tear it down tomorrow clean everything and lubricate it. Next I'm thinking about trying The Mopar trick of removing one spring, then measuring the timing curve. Im hoping the advance will all be in around 2,000 to 2500 rpm. Then if I have to weld a little to limit the advance I will. I saw on the Centerville's page Nails like 30 degrees total. Now how do I tune the vacuum advance? I'm guessing I have to drive the car around and measure my part throttle low rpm vacuum and then put the distributor back in the machine and see what time timing will be at those readings? Then add a stop to limit the vacuum advance?
The vacuum will be changing so fast, you won't be able to measure it, so don't bother. Make an adjustable stop for the advance unit and start out with 10* crank timing, ( 5* on your machine ). I use 16 gauge sheet metal with a slotted screw hole as a limit. Use one of the hold down screws on the advance unit to hold the sheet metal, fold the edges over so it stays in place. You will need to drive the car and see how it acts and adjust from there. Get one of the Accel advance curve kits and use the springs, the weights likely won't do you any good. Also keep the rotor on when testing, sometimes the weights hit the rotors and act like limits. You would like the total advance to be all in just above or at your normal driving rpm. Vacuum advance will be added to the mechanical, 40+ under light throttle. Mechanical full advance should be 30* if that's what the engines want.
Thank you. So is my theory right that I have to limit my mechanical to around 12-15 degrees total plus initial to get my 30 degrees?
Yes, initial plus mechanical equals total advance. Initial of 8 to 10 degrees would be typical then 20 to 22 degrees of mechanical if you want 30 degrees total.
You need to have initial timing + mechanical, so 8 to 12 mechanical + what you set the timing at. Some engines like more timing at idle some less, depends on how it cranks and starts. Then drive testing begins.
On the vacuum advance; too much vacuum advance gives you a spark knock on light acceleration. It goes away when you really open the throttle since the vacuum advance goes away. You have to drive it and play with a limit of some kind until it no longer spark knocks on light acceleration. That should give you the optimum vacuum advance for your engine.
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