I recently raised my timing advance even further in the 18 psi range, going for around 6 degrees of advance over the FM defaults- this ramped from somwhere in the 10 degree to 20 degrees of advance range from high to low rpms.

Tonight it was cold so I went out and hammered it. The car felt ******* FAST, but I got a medium sized knock event at the top of the RPM range where I was running

18.5 degrees at 6500
19.5 degrees at 7000
20.0 degrees at 7500

Oddly, despite the very mild curve beyond 6500 rpms, I got one knock at 7000 and a bunch at 7500. I added some fuel and didnt get any knock at 7000 but got one event later that night at what I believe was 7500.

Anyway, what is causing this? Is it too much advance or is the spark breaking up too much and causing uncombusted crap to heat up the chamber at high rpms?

I have temporarily gone back to 3 degrees over FM defaults at 18 psi to be safe.

 

Are you running a MSD or anything for the spark? I had a similar problem and figured out it was the spark shutting off due to pressure spikes. Close you gap on the plugs some and see what happens.

 

Are you running a MSD or anything for the spark? I had a similar problem and figured out it was the spark shutting off due to pressure spikes. Close you gap on the plugs some and see what happens.