Why am I breaking valves???? -=Roadracing=-
08-27-2007, 07:55 PM
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On The Tree
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Why am I breaking valves???? -=Roadracing=- In the last year I have broken 2 valves on 2 different motors and I can't help but wonder why.
The car is a 2002 Z06 that I run road racing track events with, I'm not hard on the motor, I shift right at or a little after 6k, 6200 at the most. I haven't mis-shifted/overreved either motor. (Rarley I'll hit the gate instead of the gear but I never aimed for 4th and hit 2nd) I heel toe downshift and blip the throttle to match revs coming into corners but not anything out of the ordinary at the track.
Tunes are conservative running less than 13 to 1 AF usually between 12.5 to 12.7 on the WOT pulls.
The car has full bolt ons, 1 3/4 Melrose Motorsports headers, Random cats, stock Ti mufflers, DeWitt's radiator with internal engine oil cooler, Blackwing, ported throttle body (by LPE), ported LS6 intake (by LPE).
1st motor stock LS6 bottom end with LPE heads, LPE GT1-1 cam (229in/242ex .631"in/.631"ex 114 lsa) stock LS6 valves, Comp 921 valve springs, Comp push rods, and Harland Sharp rebuilt stock rockers. I put about 2k miles on the motor and the way I figure the head of the number 8 exhaust valve broke off and blew the motor, broke the timing chain and cracked the block. I've also entertained other ideas, such as valve float, but I don't think the lightweight valve floated with a 921 spring, if anything I think we had too much spring for that valve. So there I am with a blown LS6, I figure this time I will have LPE build me a motor from top to bottom so it's done right.
2nd motor LS6 stoker Callies Racemaster crank, Manley H beam rods, JE pistons, LPE heads, LPE GT11 cam (215in/231ex .631in/.644ex 118 lsa), (I think the valves were Manley but I do know that they were Titainium intake and exhaust, Ferrea 99100 valve springs (150#@ 1.800" 475#@ 1.250" CB 1.050"), Comp pushrods, and T&D shaft mount rocker arms. This time the number 3 exhaust valve head broke off and took out the head and the block.
So WHAT THE HELL!!!!! Both times I tried to keep the valve train lightweight to minimize the chance of valve float etc, I keep the revs down and both times a valve head breaks off. Do I just have the worlds worst luck or am I missing something here?
The car is a 2002 Z06 that I run road racing track events with, I'm not hard on the motor, I shift right at or a little after 6k, 6200 at the most. I haven't mis-shifted/overreved either motor. (Rarley I'll hit the gate instead of the gear but I never aimed for 4th and hit 2nd) I heel toe downshift and blip the throttle to match revs coming into corners but not anything out of the ordinary at the track.
Tunes are conservative running less than 13 to 1 AF usually between 12.5 to 12.7 on the WOT pulls.
The car has full bolt ons, 1 3/4 Melrose Motorsports headers, Random cats, stock Ti mufflers, DeWitt's radiator with internal engine oil cooler, Blackwing, ported throttle body (by LPE), ported LS6 intake (by LPE).
1st motor stock LS6 bottom end with LPE heads, LPE GT1-1 cam (229in/242ex .631"in/.631"ex 114 lsa) stock LS6 valves, Comp 921 valve springs, Comp push rods, and Harland Sharp rebuilt stock rockers. I put about 2k miles on the motor and the way I figure the head of the number 8 exhaust valve broke off and blew the motor, broke the timing chain and cracked the block. I've also entertained other ideas, such as valve float, but I don't think the lightweight valve floated with a 921 spring, if anything I think we had too much spring for that valve. So there I am with a blown LS6, I figure this time I will have LPE build me a motor from top to bottom so it's done right.
2nd motor LS6 stoker Callies Racemaster crank, Manley H beam rods, JE pistons, LPE heads, LPE GT11 cam (215in/231ex .631in/.644ex 118 lsa), (I think the valves were Manley but I do know that they were Titainium intake and exhaust, Ferrea 99100 valve springs (150#@ 1.800" 475#@ 1.250" CB 1.050"), Comp pushrods, and T&D shaft mount rocker arms. This time the number 3 exhaust valve head broke off and took out the head and the block.
So WHAT THE HELL!!!!! Both times I tried to keep the valve train lightweight to minimize the chance of valve float etc, I keep the revs down and both times a valve head breaks off. Do I just have the worlds worst luck or am I missing something here?
08-27-2007, 09:05 PM
#2
Staging Lane
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I do belive your gremlin is spark knock,since it is the exhaust valve it keeps happen to. Detonation is no fun, been down that road to many times, that has happen to me as-well. It seems that the pcm is advancing to much timing .
08-27-2007, 09:28 PM
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On The Tree
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In the 383 I was running Torco fuel adative and all 3 times the motor was run at the dyno there was no spark knock at all. Also I would think that the knock sensors would pull timing if that was the case, or at least give me a code. I guess the temps at the track are going to be different than at the dyno, but I still think that seems odd. But so does loosing the head of your valve. 