I tried for days now to make my knock counts go away.
What happend is that when I downshift hard ( manual car ), I always get sparkretard, around 3-4 degrees, then it goes away, pretty fast, and the car starts to pull hard.
I always thougt this whas due to a lean spike during tip-in.
Now I made several runs with my zt-2 WB, and I can confirme that I dont have a lean tip-in during downshift.

Then I tried a diffrent approach. I just downshifted without touching the throttel ( TPS at 0% ), and I got the same amount of spark retard as before! Then I tried to downshift soft, instead of release the clutch fast I engade it softly, no spark retard.
Same goes for my 0-60 runs. If I reve the engine and let go of the clutch fast, same kind of spark retard. But if I go WOT and slip on the clutch no retard.

I also tried to take away up to 10! degreees of spark, no change, then I tried octane booster, same thing.

This made me think this is mechanical related. Headers touch the frame, exhaust touch something, etc. Its hard to see under the car what it could be. Right now I cant se anything touching anything when it comes to exhaust. But then again the engine is not under load.

Has anyone experince issues as this before? And can I rule out real knocs with my methods?

I cant read my plugs as for now. Because they are the same as when I DID got real knocks ( during the first tuning sessions ). So they still got some dots on them from that time. Got 8 new ones that going in today.

Thanks for your time

Devil....

Sounds like you are on the right track, check your bellhousing bolts, clutch linkage etc.

Might need to play with the Burst Knock Retard stuff.

Got it. Good tips about the bellhousing bolts.

Thanks Grumpy. Do I need a hack to change that tabel? Because I dont see it in tunercat?

Its a vette 1991 6spd


Thanks for all the tips so far..

tt