I raced the IHRA divisional at US131 this past weekend. I qualified #8 out of 41 with a 14.038 pass. Unfortunately, I never got to the first round.
I raced in the combo race Sat. night, won 3 rounds and blew the #4 piston. Didn't feel it on the run at all, but the tech buys pulled me over after the turn off for oil smoke. There was oil blown out of my breather filter and all over the exhaust (huge blow-by). When I restarted the engine, I had a definite missfire. Went to the pits and checked everything out, plugs/wires seemed OK, so I did a compression check - ~130psi in all cylinders except #4 - 60psi.
So, here's the run down. Plugs all looked good, slightly rich actually. No A/F and no scanner, but it's in the works. The car has only 18 passes on it total. 2 of those passes were at 18psi boost, I went back down to 15psi for this weekend (didn't want to go to fast). The first 10 or so passes were at 5-12 psi. It's a race only car, so that's all the miles it has on it, plus driving the return road. The engine was all new this season. Fresh block, head, pistons, rods, bearings, you name it. It has only ever had Torco 110 race gas in it. Today, I pulled the head, and there was a semi-circular melted spot on the #4 piston near the exhaust valve. So, I pulled the piston, no cracked ring lands like I expected. But, there is some ally on the cyl walls that should clean up. Also, the combustion chambers on 1-3 looked slightly black (rich) #4 was still clean around the intake valve, but black around the exhaust. Pistons are Sealed Power cast (the only piston allowed when I bought them, Ross are now allowed and may be my replacement). I'm running my own 3-bar cal with +20 injectors. I know the cal is conservative, and it's setup to be safely rich at WOT.
Before I just bolt it back together, what caused #4 to die?
Timing? Base timing is set to 12*. But, the race convertor I put in had no timing mark, so I had to make my own. It could be off by 2-3 degrees, I guess. But why would only #4 melt?
Fuel? They're +20's and the clyinders don't look lean at all. I suppose #4 injector could be clogged or just off.