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Preventing Preignition/carbon Deposits

kismetcapitan
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kismetcapitan Apprentice

kismetcapitan

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I had a chance yesterday to compare some pistons. The first were some N1 pistons - they had a bunch of little holes on the sloping sides - clear sign of detonation. Then I took a look at my old pistons from my melted RB26. What I thought were black melted holes were actually thick carbon deposits built up on the piston surface. The only surface distortion was at the piston edges, where searing hot gas made it's way down to melt the rings and took a bit off the pistons edges as well.

What causes heavy carbon buildup in a four-stroke engine? Is it from running rich, or just crappy, dirty Korean fuel (even if it is 100RON)? Or something else?

Avoiding knock is pretty straightforward - retard timing, higher octane, running rich, etc. But what about avoiding runaway preignition? Highway cruise, 5th gear, then suddenly without warning, everything melts down, you get the white smoke of death, and it's all over. I'm not the only one to have lost an engine this way.

If the cruise portion of the map is lean (for fuel economy), perhaps dangerously lean, how would that in itself blow your engine? A hundred times on the freeway without incident, then on the 101st you get a nasty surprise. Is the safe course of action to simply run rich all over the map? Wouldn't that exacerbate carbon deposit buildup?

I thought I was the only one to have such "bad luck". Turns out I'm not. I have thoroughly studied preignition and know what causes it (glowing spark plugs, glowing carbon deposits, glowing sharp edges). With the flamefront igniting as far as 160 degrees BTDC things get too hot in milliseconds.

Would running fuel detergent additives help, I wonder? I've always viewed that rack of bottles in the shop as nothing more than snake oil. Or does that crap actually worsen things?

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