that piston might be the new esr version but i dont care for how they machine the sides. it might be letting exh into all 4 transfer passages but its hard to tell without putting the piston in there and looking
something neil didnt mention but the passages can turn black if you simply dont have enough blowdown area to let the exh out fast enough
im not trying to diagnose your problem, hek you may have several problems for all i know. just letting you know some of the reasons that will cause the black
Your right about that piston on the machining. I wish they only had the machining like how the CR pistons are, where the machining was only behind the wrist pin. That way, the only chance of port linking would be from around the wrist pin center.
The whole problem, stems from the aux exhaust port windows being to far around in the bore & being close enough to the center to match up with the main transfers. I spent a bunch of hours trying stuff, cut sleeves & pistons in half, like a cut away, just to check what was happening.
When the linking is bad, the fresh crankcase charge is so weak, from so much being lost to early out into the exhaust, it cant keep the transfers clean & the engine ends up with more stagnet charge in the bottom end than fresh charge.
When I get his cylinder in, I'll do a degree on the ports & check that blow down.
Something else I'm really wondering, how much real performance are we gaining, from the lighting of those pistons from that machining on the sides. Would like to test one with no machining done to the sides, just to see what changes. I would gamble & say none that the average user would notice.
Neil
