Well, I'm speaking to this issue based on many years of experience building vintage American V-8's, not from direct experience with the 850 motor. You've already hit on some of the primary causes of knock, low octane gas and high compression, high fuel/air mix temp and high engine temp. You've already said you're running 93 octane fuel, so unless the station you're using is pulling something funny you can rule out that cause. Maybe try a different brand of gas just for kicks, you'd be surprised the difference it can sometimes make. I never use Sunoco, had bad performance from it consistantly years ago, never been back. High engine temp, you would see that on your temperature gauge. If the cars not running hot then that's out. High fuel/air temp, unless you changed something in the intake plumbing that shouldn't be a problem. However, if you have a vacuum leak somewhere in the intake route that CAN cause higher running temps, as you've then leaned out the mixture with the additional air thats being sucked in, and a lean engine runs hotter than a rich one. But, the engines ECU should have been able to compensate (to a point) and probably would have thrown a code that would tip you off. Higher compression ratio, unless you put on a milled head, that should be out also. However (theres always a however), large carbon deposits in the combustion chambers can raise the compression ratio if big enough, since they take up some of the available volume within the cylinder bore. Trouble is, this never happens uniformly across all the cylinders, so you would probably notice the car running funny if it ever got that bad. Really though, this is pretty unlikely, you can run up to about 11:1 compression on pump gas (my last Mustang was running 10.8:1 and was fine on Premium), and it would have to be some damn big carbon deposits to get an 850 motor up to 11:1 compression. Manifold pressure, is your car a turbo? maybe there's something going on with the ECU and it's control of the boost pressure? I don't have alot of experience with computer controlled forced induction, so I'm not even going to offer anything here. If it was my car, the first thing I would look for (other than codes) would be a vacuum leak in the intake stream or a bad knock sensor. Also, maybe the distributor has something going on with it. If the knock sensor is saying it's seeing knock, and telling the distributor to retard the ignition timing, maybe the distributor is not getting the message, or not able to do it. Still, I would think all these things would throw codes. Either that or you've got some really bad gas...