Or in this case... when you jet too lean. It's not necessary, but I'm going to share my lesson with you all, save you some time and money this way. I typically run 91 with a bottle of Lucas octane boost on the street and 100 sunoco at the the track....not this time. First run was shit, garbage reaction almost half a sec....left okay..but spun in 2nd and peddled for 8.0 in the high 80's. Track is just over 2000ft, it was a hot dry day... I run one jet'75' under stock'76' @500 ft ... I dropped to '74' primary and took some slack put of the msd cap "they always have 2 degrees over movement" and went for another test run.... hooked hard on street tires 'track prep is decent there' but then got some hop at the top of 1st....its pulling harder, great, then hit 2nd....it pulls into 6200 or so and then it goes away, no power... let off the pedal and as I did I heard the old "rocks coming off the tires into the wheel well noise" and knew something was in pieces, turned it off and just coasted through the traps.... got out and looked for oil and shit sticking out of the pan, nothing. Towed to the pits Pulled the plugs and coolant shot out. Proceeded to pull the carb, valve covers, all plugs. It shattered a piston,pin and the H beam lumberjacked the cylinder through and coolant filled the crankcase and went in through that cylinders opening valves into the intake and "plane sharing" cylinders. 'Dual plane intake' so you can figure how. It was no.5 Could have been the tune, easy, could have been past tuning that knocked off a ring land and it was a ticking time bomb.. I'm leaning more toward the tune that day. This motor consists of the following '78 360 block .040 KB hyper quench domes set @.030 quench .004 skirt Herbert street solid roller .575 251@.050 108 288dur Morell rollers drop in style Portered J heads 284/196cfm 2.02/1.60 K motion 800 220lbs@ 1.75 seat 495 open Comp magnum arms Ohio crankshaft nodular iron 4" crank Ohio h beam rods w/arp 2000 cap screws 10.1 comp 8.9 dynamic =185 psi cranking Mildly ported LD340 dual plane Demon 780 dbl pump TTI step headers 3" exhaust to bumper 245 60 14 bfg 3.73 gear 4spd 3200lb or so car weight As a friend would always tell me... "always remember.. if you're not breaking shit,you're not learning" I had a great time, I was even excited to find out what went. I'll post more pics as I get it all out of the car, but I can already see it all, windowed that cyl. In the end, the crank held up, the rod never left it as a matter of fact, the lifters are cherry, the cam will need touched if not a regrind, no bent valves.... It is what it is....and that is I already have another block in the machine shop as I type this... I love this shit.