Spark knock
Tech Contributor
Joined: Aug 1999
Posts: 14,373
Likes: 6,371
From: At my Bar drinking and wrenching in Lafayette Colorado
A lean condition will contribute to detonation, but most often the problem is timing related. If your power piston is stuck in the full lean position or if the carb is not set up right, it will aggrevate the problem.
Most common detonation issues are from:
Most common detonation issues are from:
- Excessive total timing (set total to 36 if you have stock-type heads. "Fast-Burn" will not take more than about 28-32 total)
- Total timing coming in too fast (limit the 36 total to not come in any quicker than about 2800 rpm on a lower-compression engine. If you're in the 10:1 range with a mild cam, you may need to slow it down to 3500 - 4000 rpm)
- Incorrect vacuum advance control unit in use. Many stock units will pull in over 20 degrees of vacuum advance, and that's too much for a performance engine running 36 degrees mechanical timing. Most performance engines will not take more than 16 degrees of vacuum advance, and fuel characteristics in many parts of the country now require that you limit vacuum advance to about 10 degrees.
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
moving from the more obvious to the less likely, cross-over can cause non-timing related knock, especially intermittant and when not under load. If this is the case, check to be see if any wires are touching. This is more likely with HEI or old wires.
Good luck
Good luck
Safety Car
Joined: Oct 2005
Posts: 3,570
Likes: 1
From: Algonac Michigan
