I'm a proficient tuner, and I use det-cans attached to the cyl head (usually passenger side IM bolt) to audibly monitor knock while street and dyno tuning. I've noticed that often, MBTT coincides with infrequent "sparkles" events which are audible in the cans. These events are not as strong as a definite spark "knock" which is very distinguishable and Ive verified this with piezoelectric logging, but they seem like a precursor to "knock" or like some kind of pre-detonation, or detonation restricted to one area of the combustion chamber.

The last dyno tune that I performed saw a difference in 18ft/lb across the 5500-7500 RPM range (GSR stock rotating assy-Turbo@10psi) with 4 deg of timing added in that region. On the dyno, there were few "sparkles" knockish noises after adding this timing (from the street tune), but once we put the car on the street, there were plenty of these sparkles events after 2nd gear happening. I immediately pulled a plug after a street pull and there were NO signs of det on the plug... instead there was a nice timing strap on the ground, and colors that suggest great AFR's across the board. Is it normal to hear this clickidy clackidy quiet precursor to detonation in the can's with engines tuned on the edge?

 

well in order to really help, we need to know the materials used to make your DET CAN

 

How much load did you have on the dyno. The amount of load that is put on during a pull will make a big difference on an engines performance. What type of dyno is it?

 

inerta dyno. we were doing 3rd gear pulls from 2600RPM to redline, each pull took about 8 seconds

 

That probably is detonation... it's just not enough to destroy the engine quickly.