Has anyone toasted a forged aftermarket #7 piston?
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Lean mixtures or detonation can kill any type of piston.
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That I understand. I'd like to know if someone has had the same problem with an aftermarket piston in the 5 or 7 cylinder. I changed mine out to forged Mahles. When I did I could see how easy it was for any of the stock pistons to let go. That hole in the top of the factory piston comes very close to the top ring land.
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Originally Posted by LV Vette
(Post 1560159256)
I hope this is not a stupid idea, but if # 5 and #7 are the problem due to lean AFR, what would happen if you use a slightly larger injector on these two? It just popped into my head, so what do you think?
Thanks, Clayton from Las Vegas :flag: |
Originally Posted by RED99
(Post 1560159274)
I"m thinking a single plane carb style intake with a 90° elbow on top where the carb would go would work better for F/I. This would push the air down in the center of the motor and equally divide the air.
Do the maggies have the same problem? |
Originally Posted by APS
(Post 1560159369)
It's definitely a piston heat related issue as those cyliners run much hotter due to much leaner air fuel ratios. It's quite easy to see this when you actually measure the EGT and AFR on each individual cylinder.:)
Peter Can you quantify this, Peter? For instance, how much spread do you see between the AFRs from cylinder to cylinder? |
Originally Posted by leojnknsC5
(Post 1560215252)
YOur computer will be constantly in a state of confusion from adjusting the air fuel ratio when 5 and 7 fire. The cylinder after 5 or 7 will end up too lean.
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What about a different heat range plug in #5 and #7?
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:lurk:
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Originally Posted by Warp Factor
(Post 1560219883)
I'd think the opposite would be true if 5 and 7 are leaner to begin with (as Peter stated) and injectors are selected to help even this out.
Anybody who's blown 5 or 7 would be wise to pull the composite intake manifold and replace it with one that centers the incoming air to the center of the manifold, like a carbed manifold. Then see if 5 and 7 still go lean. |
Originally Posted by APS
(Post 1560158576)
Bill, Number 5 and number 7 cylinders generally fail first as those cylinders run a much leaner air fuel ratio than all other cylinders. If you run lamba probles on all 8 cylinders as I have you will see why the #5 and #7 cylinders fail frequently. :cheers:
Peter If you are showing say 11:1 AFR in the collector, about how much leaner is the #7 running? |
:lurk:
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Something else to consider is switching to a Evans Water pump and T stat, they noted much less flow on the odd side bank, their pump evens out the flow on both banks and flows alot more than stock. May help keep things more stable...
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I have been thinking the same thing. Along with there special waterless coolant.
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Originally Posted by 427 LS1
(Post 1560223554)
Something else to consider is switching to a Evans Water pump and T stat, they noted much less flow on the odd side bank, their pump evens out the flow on both banks and flows alot more than stock. May help keep things more stable...
I have been impressed with this setup over the years, on every engine type I have switched it to. Well worth it on a road racer. I have had intake flow problems over the years on various engines, and they all have one or 2 cylinders running leaner than the others, and I just work the intake until I get the flow much closer to matched. 2% or less cylinder to cylinder flow variation seems to do the trick. The guy that said do not push them to the freaking edge had a very good point, which leads to the dyno and AFR measurement arguments, as well. If your tuning data is not perfectly accurate, in combination with "tuning for numbers", these things tend to happen more often. Match the airflow, stay off the edge, use accurate tuning data, and the problem % goes way down. |
GM should have known after 200 sprayed passes, upto 250rwhp hit, that upping the shot to 285rwhp on an absolutely bonestock longblock LS6, I would finally break a ringland. See my point, these motors are monsters from the factory, and with a spot on tune can go for some time at the limits. The only reason I had problems at 285rwhp was I messed my tune up and added 4* timing instead of pulling said timing. Can you guess what cylinder went with the resulting mega temps this motor saw, and 665rwtq at about 3500rpm. Oh and the a/f was 10.8 through out the dyno run.
http://www.fquick.com/images/vehicle.../206333150.jpg http://www.fquick.com/images/vehicle.../206333149.jpg Robert |
Originally Posted by EnglandGreen
(Post 1560155934)
Toasted 5 & 7. The usual suspects.
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just went to the machine shop to check what the problem was on mine today. Of course, lucky number SEVEN!!!
mine isn't too bad.....looks like a slight flat on the piston spot where it may have gotten too hot and some dimples in the cylinder wall. So what should I do on the rebuild?!?!?!?! brett |
rebuild forged..You might need a new block as well. Have it checked real well...
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