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Looks like detonation to me. A few reasons why detonation occurs is Cylinder temp too high,Very lean mixture,Low quality fuel(low octane) and too much spark advance.
The section on the skirt which is blue and carved out looks to have been caused by the flame travel.
 

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this is a hyper. piston if that changes anything. How about rich?

yep problem #1 KB Hyper

how muck n2o was on it?

could you be more specific of the combo and tune?
 

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Discussion Starter · #12 ·
its a sbc 350 street motor. was using nx gemini twin plate 150 jets. 8 psi of fuel pulled 5 degrees from 34. 1000#s bottle pressure. 1/4 mile pass.
 

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The piston skirt does not appear to show any dry scuffing which is normally seen on a rich tune.
What fuel where you running on the gas?Maybe try a better fuel next time and a set of forgies!!!!
 

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I have made a lot of passes with the wifes car, SBC 383 with KB Hyper-U-Junktic pistons using nitrous. Goes 12.4's on motor, 11.5's with a 125hp shot. Wrong fuel, 93 Super Unleaded, wrong plugs, FR2LS AC (extendeded tip), ran 12.0 A/F ratio on wideband and only pulled 4 degrees. Can't believe I never melted that thing!
 

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Who designed the cam for that and what is it supposed to be? How was it degreed in?

How much compression do you have and what is the quench/squish distance?

What is the engine and what is the header size?

Ed
 

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From my own experience with hyper pistons... looks like you lifted a ring land. Maybe not on this pass but some time recent. From there the flame and pressure were gonna go down. Remember something about the NX kits. The horsepower ratings they give with their tuneups is rated for wheel HP. So look at that 150 shot as really close to 200.
 

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Lifted a ring land, probably on an earlier run. This causes a bad ring seal so oil gets in past the rings, detonation occurs and burns the piston up next pass. You were probably too rich to begin with.
 
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