[SLP IROC-Z]

Cars been running rough cold lately. Thought it might be plugs since they have over 20k hard miles. After checking the misfire pids starting it cold cyl 4 got 73 misfire counts right off the bat. I pulled the plug and did a compression test I got 200psi at first then 190. After had the compression tester off some coolant dripped out of it. I wasn't sure if it was residule from something else we worked on or from my engine. The car was down a bit on coolant. I filled it uo and put a new plug in and it seemd to run better. Well this am it wouldnt even turn over. Pulled #4 plug and cranked the coolan out. Drove it to my shop, getting ready to pull the topend first compressin and leakdown test all the cylinders. I guess cracked head or bad headgasket. If its the headgasket that concerns me. Ive never had to deal with much knock retard with this thing. I run 22-23* of timing at WOT, I can run 26 but it doesnt go any faster, doesnt knock either. Its never got hot. Never touched the rest of the timing table (stock z06 table).

Heres the plug from that cylinder.