122_Canuck wrote:
I just looked that first part up - frick, marketing bastards screwed me again (see
http://www.europeancarweb.com/tech/0503 ... to_12.html)...now if I got it up to 95 octane it is still shed loads better than the weak piss 91 I was getting as premium in BC. Points - oh if I could get my hands on those pricks.
Yep, the buggers. You'd swear it works, though... wonderful what the wallet dyno will do!
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The ignition curve is not entirely unrelated as the combustion temps could be creating the heat. I don't get dieseling all the time - only when the engine is up to temp. So screwed up timing could be part of the issue (and the related issues of idle speed etc). Your calcium point has me thinking...I have no way of knowing if Parker did anything by way of cleaning inside and I did the best I could, but didn't tank it (as they don't do that anymore). I'm not opposed to having a little look-see this winter when the car is sleepiing.
The point I was trying to make is that I will bet that the temperature of the combustion chamber surface drops rapidly once you bring the car back to idle. If you've got 5-10 degrees of actual timing advance (remember Greg's crank pulley being way off...) then while you're at idle, things are going to cool off rapidly. Try idling the car for a minute before shutting it off. Also try verifying the crank position via chopstick.
The other issue is that I've only ever had dieseling on an engine with the header directly under the intake manifold. You could try some header wrap - it wouldn't take much to insulate the first foot or so of the primaries. I've got some if you'd like to give it a whirl this winter.
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Cam timing also got me thinking. I don't really want to swap out the cam, but part of me wants more power and I think I could get a more radical grind. It was timed straight up (as that's the only way you can time them as each tooth is something like 6 degrees) - so unless the cam was not ground straight (

) then that's my only option unless I get offset keys made. I'll have to put the degree wheel on it again as I can't recall the numbers, but I don't recall it being off.
A more radical grind would lower the DCR, as would a more retarded cam timing for what you've got. Each tooth on the crank pulley should be closer to 15-20 degrees, shouldn't it? Remember to divide your camshaft teeth into 720, since it turns at half the speed the crankshaft does. Regardless, if you were off a full tooth you'd KNOW it, but when my cam once jumped a tooth, the car ran HOTTTTT (and it was winter-ish). Granted, that was with a B21, and the cam/dizzy can't be counted on to jump in the same direction.
I should make the point (that I ignored earlier) that because you've got longer connecting rods, your R/S ratio is different from other B20s and your pistons dwell at TDC for a fraction longer. The upshot is that you'll need less spark lead than an otherwise identical B20. Actually, you'll need a different camshaft too, but that's another story...
Edit - your link is good reading. The only thing I've got to question is that pre-ignition was silent, from my understanding. Basically you're igniting the fuel quite a bit BTDC, so it's mostly burned up by the time the piston generates much pressure. Then as the piston comes to TDC, the pressure is crazy but there's nothing left to burn, therefore no ping. Tons of heat, though, burning through things like pistons & valves...