Quote:
Originally Posted by kmoose
. . . If it was a 2 stroke that would be more of an issue but internal piston oiling on a 4 stroke pretty much eliminates that issue as many car motors for decades turn fuel and spark off to cylinders to improve fuel economy. It's not an issue and it wouldn't surprise me if Evinrude makes a move in the same direction to reduce weight down the road. . .
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With regard to the fuel starvation/lean combustion/overheated piston issue, the 4-stroke motors do have one advantage, i.e., the wasted exhaust/intake stroke reduces the time that the piston is exposed to extremely high combustion temps by 50%, which would reduce the tendency of the piston to overheat/expand and seize in the bore. However the other problem that occurs with very lean combustion is detonation, and both 2 and 4 cycle motors are equally at risk for this destructive phenomenon, which can quickly fail rings, ring lands, or even blow holes in the piston, either of which can score the cylinder walls. Oil cooling of the pistons does not necessarily help reduce small local hot spots or glowing carbon deposits on the piston surface which can trigger detonation. Although you
MIGHT be able to hear the valves rattling caused by detonation on a 4-stroke, there is no such warning on a 2-stroke, so BRP has installed knock sensors on the 3.3/3.4L G1 E-TECs and all the G2 models. If the EMM detects knock, it will enrich the fuel mixture and retard spark, but if that isn't effective, it will put the motor into safe mode and display a "knock detected" warning on the digital gauge. They've also used a higher strength/higher temperature NASA aluminum alloy for the pistons on all E-TECs to provide additional margin against these sort of problems.