View Full Version : detonation

08-15-2003, 03:03 PM
I have a pro billet 8361 distributor with the 18 degree bushing and one light blue and one light silver spring. Initial timing is at 8 degrees. With the vacuum advance plugged I can run the engine above 3000 rpms without detonation but once I hook up the vacuum advance it starts making a popping sound at 3000 rpms, is that the sound of detonation? I have a limiting plate for the vacuum advance, is it a good idea to put it on? When the car is in park and I am checking the timing it makes that popping noise but I can't hear it when I am driving it on the street. Does the advance curve change from when the car is in park in the garage adjusting the timing and punching the throttle to when you are driving the car on the street or freeway?

Thanks for your help,

08-15-2003, 06:58 PM

The vacuum advance is only operating when you have vacuum applied to it. Generally, when you accelerate from a stop sign or when a heavy load is applied there is no vacuum so the vacuum advance is not activated. To check what is going on with your system, place a fully degreed timing tape on you harmonic balancer and then check the timing with the vacuum advance connected and then disconnected. At idle, with the vacuum advance disconnected your timing should be at whatever point you originally set it at. Now, plug the vacuum hose onto the vacuum advance and recheck the timing. Since the engine is idling with no load on it, your timing should be advanced by whatever you set the initial at plus whatever amount you have on your vacuum advance. Here is how to calculate your total timing.

Without Vacuum - Initial Timing = Timing at idle
With Vacuum - Initial Timing + Vacuum Advance Timing = Timing at idle