this is a friends motor and im posting this in hopes that you guys can help diagnose what happened. obviously detonation but im not exactly sure why. this was cylinder #4. the others look ok and the bearings are all still perfect. Here is the combo. 374 cubic inches (4.125" bore - 3.500" stroke), JE flattops, AFR 210 eliminator heads (75cc chamber for 9.3 compression ratio), mechanical flat tappet (252* in at 0.050" - 260* ex. at 0.050, 1.6 intake rockers, 1.5 exhaust rockers), Super Victor intake with some plenum work, CSU 830 carb, e-bay turbos with the following specs - 57mm x 75mm x 0.070 A/R cold side - 58mm x 74mm - 0.068 A/R hot side T4 compressor and turbine. Homemade log style manifolds. Air to air intercooler. TH400 with custom 9 1/2" converter, GearVendors and 3.73 gears. 28 x 10.5 slicks, car weight approx. 3800 lbs. Hadn't gone over 15 lbs with this setup on turbo's yet, had run over 20 with previous Procharger setup. Timing on this pass was 28* using 93 octane.