OK -

I have an 89 Supra, Turbo. Added elbow/downpipe, cooleeze accordian replacement, 550s, Lex AFM, RSA air filter, EGR blocked off, shimmed wastegate to ~11 psi, on 93 octane pump gas.

I had timing set to 10 degrees with check connector jumped, and TPS adjustment confirmed closed at idle. Car would ping, and then pull timing at 90% or more throttle.
So after checking air intake, fuel pressure, vacuum leaks, spark plugs, and finding no codes, I set the timing to 5 degrees. Pinging immediatly more noticeable, any load past 60-65% throttle.
So I set timing to 12, no pinging, then 15 degrees, now it has only occasional ping (like if I do a full pull, just after shifting, boost peaks to ~14ish psi.

So my question is: Why does it ping more the farther I retard the timing? I thought the opposite should be true - more timing - more pinging. Is there a problem that would cause this symptom?

Thanks for reading -

are you POSITIVE that the cam timing is set correctly? follow the TSRM for lining everything up and triple check that....

Either the cam timing or the CPS/distributor is off.

Pulled timing cover, both cam marks on the dot. Will check the CPS.

Thanks, will let you know.

line it up @ TDC on cyl 1, make sure everything lines up. then pull CPS and realign....

A customers Cressida did that something like that. Setting the timing to the wrong spot made it run correct, and set to 10 made it run really bad. The distributor had been out and not put back in correctly.