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03-16-2020, 01:04 PM
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Lance,
Do you see any signs of detonation?
Pappy
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03-16-2020, 02:11 PM
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Quote:
Originally Posted by mfain
Lance,
Do you see any signs of detonation?
Pappy
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A lot on #4, the one that cracked and burned and just a couple small pits on #1. Tops of all the rest of the pistons look great, including #8 with broken ring land.
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Lance
1985 Monte Carlo SS Street Car
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03-16-2020, 02:21 PM
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Quote:
Originally Posted by SSLance
I'm still very happy with the power this combo made so I'll not be making any drastic changes to the recipe, just fortifying some of the weaker parts inside and putting it all back together once again. It'll just take a bit longer and cost a bit more is all.
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Same situation with mine. Just upgraded the weak parts. Rods, crank. One thing we did was replace all 8 sleeves (Brodix aluminum block). We needed to replace 4. Then we would have needed to bore them .030" over, to match the other 4. Or, replace all 8, and now have a standard bore block, which will allow for some freedom in the future.
Only money...
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CP29
There is no such thing as too much power, or too much tire!
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03-16-2020, 02:23 PM
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Quote:
Originally Posted by SSLance
A lot on #4, the one that cracked and burned and just a couple small pits on #1. Tops of all the rest of the pistons look great, including #8 with broken ring land.
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Might want to investigate the source of the detonation - usually an octane, timing, or AFR problem. Cast pistons tend to give up early (broken ring lands or cracks at the wrist pin), but even good forged pistons don't like detonation. Were you running an AFR gage or monitoring EGTs? With a nominal compression ratio, octane should not have been a problem, barring excessive timing advance. Sounds like there might have been something in the tune at some point that was causing problems - just my opinion.
Pappy
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03-16-2020, 04:41 PM
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I was not data logging at the time, but I have plenty of WOT logs showing the tune performing as desired.
I'm still leaning more toward something happening in that cylinder that raised compression or lowered octane enough to cause the melting of the edge of the piston. There were several mechanical failures there and all of the rest of the cylinders were fine.
We may have been close to the edge and a minor variance put it over, not discounting that...but if it truly was only tune related, it would have shown more damage across the board and most likely would have happened earlier.
It had been pushing antifreeze out recovery tank for two events prior, indicating the start of the real problem. The burnt piston is more of a result of that problem than the tune.
But yes, I probably will back it back away from the edge next go ahead.
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Lance
1985 Monte Carlo SS Street Car
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03-17-2020, 04:05 PM
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Too bad you had to tear it apart again Lance, but addressing the possible shortcomings will continue to make your engine more bulletproof. I enjoy following your journey because except for a minor setback such as this your car is a contender amongst much higher dollar builds out there. Keep it up and let us all learn and enjoy with you as you go.
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Chris
1969 Firebird: injected Pontiac 462ci, T56
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03-17-2020, 06:02 PM
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Just throwing this out there, what were the ring gaps set to?
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03-17-2020, 07:44 PM
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Quote:
Originally Posted by CamaroAJ
Just throwing this out there, what were the ring gaps set to?
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That is on my list of things to check.
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Lance
1985 Monte Carlo SS Street Car
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03-18-2020, 08:31 AM
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Quote:
Originally Posted by SSLance
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This may be the answer you are looking for. A long rev limiter hit is tough on your bottom end, especially with cast pistons. When I had my ZL-1 built, my engine builder preferred I raise the rev limiter vs. bounce it off repeatedly.
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Todd
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03-18-2020, 09:12 AM
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OMG Todd, I had forgotten all about that incident.
You very well may be onto something there.
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Lance
1985 Monte Carlo SS Street Car
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