total timing is set at what rpm

There is a process for properly dialing in a distributor to provide optimum power and efficiency. The ignition must ignite the mixture early enough to result in maximum cylinder pressure at approximately 20-30 degrees after TDC to obtain the most power and efficiency.

1. The initial timing for your combo must be established. Setting the timing to a total number at a rpm that has all the mechanical advance in typically winds up with to little initial timing. To little initial results in a a rough idle, difficulting seting the carb at idle and power off idle throttle reponse. The initial timing can be determined very accurately but increasing or decreasing the initial timing setting in small increments to obtain maximum manifold vacuum while maintaining the idle rpm constant. Cams with a more overlap than stock will require more initial timing. It is not unusual to wind up with 20 degrees BTDC or more of initial to obtain maximum manifold vacuum. The caveat here is there can be a point when the engine will kick back against the starter before you have reached the ideal initial setting. Your choices are to back off and be good enough or add a timing retard to the engine for starting. Get this right and you will have a crisp idle, with great reponse and you will have little difficulty adjusting the idle mixture.

2. Now you need to set the mechanical advance timing. To do this accurately you need a dyno or much trial and error on the track. But you can get close with the typcial recomendations you see posted for different engines. The efficiency of the chamber design has a large impact on the number. The small block mopar open chamber head typically produces maximum power with 34-36 degrees of timing. If you have modern closed chamber heads it will be less, magnum heads for instance produce max power in the 32-34 degree range. If you have after market heads use what the manufacturer recomends. If you have a stock distributor that was set up at the factory assuming you are using much less initial timing then you will now have to much and will have to take the distributor apart to reduce the sizze of the slots. If you have a Mopar Performance distributor or MSD, Accel, etc then this is adjustable with stops or bushings. Take the total mecahnical, say 34, subtract the initial, say 20 and you come up with 14. That is the number you want to adjust the mechanical advance to provide.

3. Now you want to set up the rate at which the timing comes in. Again this can only be accurately adjusted with adyno or track time. But just like the mechanical you can get close enough. The number you see posted varies much more widely for this parameter, anywhere from all in at 2000 rpm to all in at 3000 rpm. The stock distributor had a two step rate where some of it came in relatively early but the rest wasn't all in until high 3000's of rpm. So you will need to get it down below 3000. After market distributors either come with a selection of springs or you can purcahse a kit. If you are working with a stock distributor the simplest thing is to get the two spring kit from Mopar Performance and replace the heavier stock one with one of these springs. Don't use both of them it will have all your timing coming in a couple of hundred rpm off idle. Hear driving the car will help dial it in. If you put a load on the car (slight up hill) and accelerate, if the car pings then goes away as the rpm increases then the rate is too fast and heavier springs are needed. You can try lighter springs if it isn't but if you are in the 2000-3000 range you are close.

4. Now is the time to set up the vacuum advance. The vacuum advance only operates at part throttle cruise conditions when manifold vacuum is high. At WOT the manifold vacuum is so low it doesn't add any timing. Because the cylinders are not filling completely with mixture it takes more timing to ensure it completely burns and you need to add timing and this is what the vacuum advance does. When working properly what it will do is require you to use less throttle to maintain the same speed making the car more effiecient and increase gas mileage. Start by measuring the manifold vacuum as you drive the car on level road in the 30-40 mph range. Then use a hand vacuum pump to set up the vacuum advance to be fully in at this vacuum reading (you could do this by trial an error but it will be time consumming). No drive the car and if you get any signs of detonation on throttle tip in or constant rpm that goes away the seconf you open the throttle you have too much vacuum advance. Start backing it off until it stops. Or, if you don't have it come in sooner until you do get detonation then back off.

Once you have the distributor all set up it's time to move to carb tuning. NOTE: you may need to go back and adjust your timing settings if you develop detonation.