schrad

Just built a 6.0 this winter got it in the car and put 500 miles on it put it on the dyno for 8 pull and then drag race it for 4 passes and on the 5 pass blew it up got it home pulled the motor apart and found number 7 and 8 piston gone broken rod in number 7 and number 3 piston was cracked all the way around what would of cause this ? Was turning the motor to 6500

Prorac1

iTrader: (4)

Complete specs on the engine would help to diagnose the problem.

Doug G

Stock GM rod bolts ?

Piston ring gaps too tight and butted ?

Just guesses at this point.

schrad

Stock rods and crank arp bolts in bottom end flat toped piston hypereutectic board .10 over GM hot cam and GM ls3 heads

Prorac1

iTrader: (4)

I agree with Doug. What were the ring gaps? And did you have the rods resized or checked after fitting them with arp bolts? Did you rebalance the rotating assy?

TTur1996

IMO its sounds like you floated the valves. Are you sure it was 6500rpm?

schrad

Machine shop put the bottom end together so I don't no for sure what the ring gap is and the rev limter was set for 6600 so I wasn't over rev the motor

dogsballs

i revved stock 6.0 alloy bottom ends to 7500 with stock rod bolts. 6500 should be totally fine rev wise.

i wonder if the big end was pulled out of circle with the new rods bolts, and/if they were resize (i know katech say theirs don't do this compared to arp).

PTV? Fuel? tune?

schrad

Fuel was 93 and we had chip number 2 for msd what is ptv

TTur1996

Piston To Valve clearance.

fast89stang

iTrader: (2)

I shift mine at 69-7k, and sometimes 7300 if I spin to gain back some ET, I dont think 6500 should be a problem at all.

speedtigger

iTrader: (16)

Tight rings might be evident by galling of the cylinder wall (many vertical scratches worse on the cylinders that failed).

Too tight of piston to wall tolerances can cause the pistons to try to lock up in the bore(aluminum galling on the cylinder wall often gives this away typically)

Piston to valve clearance (This will be given away by broken or bent valves in the affected cylinders

Connecting rod failure (some times this will be given away by heavy damage in the bottom end, but top of the piston might have minimal damage but not always.)

By what little information we have here, I would be tempted to suspect pistons to cylinder wall clearance issue. Either too tight causing the piston to gall and seize in the bore or too loose causing heavy side loads on the piston skirts to the point where the skirt failed and the piston tried to turn sideways in the bore. Either of these could cause the things you describe.

TTur1996

Remember he had 500 miles and 8 pulls on the Dyno on it. If it was too tight the dyno should have shown some type of regression as the temp came up.

speedtigger

iTrader: (16)

That is a very good point.

schrad

Where think and the same with the machine shop that we got bad piston

Prorac1

iTrader: (4)

What brand were the pistons?

dogsballs

7 and 8, makes my think of a heat issue (heads not bled, properly, air pocket). or fuel distribution issue, borderline tune, maybe lean out due to no jet extensions on lunch.

7&8 go, then 3 is a casualty

TTur1996

The problem is, that he just came from the Dyno shop. Surely they had it tuned right and jet the extensions in.

ls67camaro ss

What was your oil pressure like just before it let go how your head gasket look

dogsballs

The jets wont get uncovered on the dyno, fuel will only slosh to the back if the bowl on launch