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Vendor
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6,472 Posts
Not sure why you would burn the strap off the plugs if it was rich? Didn't you pull some jet out of it last race at Cecil and it picked up instead of slowing down? What jet did you pull out, nitrous, fuel or both? Did you do that on the .30 pass? Oh yeah..........make that picture smaller so I don't have to put it on my 50" TV to see it.
 

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Grandpa
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6,479 Posts
Discussion Starter · #5 ·
yea me niether! I pulled 2 jet sizes out of both nos and fuel,but I left the timing alone Hell for all I know I could have ran it a few runs with the piston like that,just seems wierd . Like I told you Sat, # 2,4 and 6
were all nipped off. 2 and 4 are ok just this one was hurt. Just getting real frustrated!! its ready to go back together now already though
 

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Registered
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373 Posts
Not sure why you would burn the strap off the plugs if it was rich?
Piston crowns up because of rich condition, too much fuel traps under the ring groove and then explodes a few strokes later and crowns the piston. Now the rings don't seal correctly, oil gets in, detonation occurs and burns the strap. All of this occured in a few seconds, probably on the same pass.
This is what I believe probably happened.
 

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Vendor
Joined
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6,472 Posts
That's a good point. Oil and nitrous don't mix well and if the/when the oil was getting past those rings it was probably a detonation fest. I think that's what happened to mine last time it blew up in 2006. Bob put a thicker ring I think on top to help keep scraping the oil.
 

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Tony McKellar
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4,812 Posts
Piston crowns up because of rich condition, too much fuel traps under the ring groove and then explodes a few strokes later and crowns the piston. Now the rings don't seal correctly, oil gets in, detonation occurs and burns the strap. All of this occured in a few seconds, probably on the same pass.
This is what I believe probably happened.
Wow, this is the explanation I've been waiting to hear,I never knew what caused the bulge in the ring lands in this type situation,thanks!
 

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Grandpa
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6,479 Posts
Discussion Starter · #9 ·
I am assuming that it would need to be way rich in order for this to happen correct?I just cant figure out why it nipped #2 and 4 also.theses no detonation showing on the head in either cyl.
 

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Senior Frog
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10,443 Posts
A new set of slugs,rings and bearings and your good to go....Me I wasent so lucky :)
I have learned that most brand name published tune ups are
fat as hell and not very good to use at all. Why MFG's feel its safer to run fat VS lean is beyond me
I made a few simple changes on my tune and went back out with alot more steam and a cleaner tune up.......
 

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SOFA KING WHAT?
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43,675 Posts
A new set of slugs,rings and bearings and your good to go....Me I wasent so lucky :)
I have learned that most brand name published tune ups are
fat as hell and not very good to use at all. Why MFG's feel its safer to run fat VS lean is beyond me
I made a few simple changes on my tune and went back out with alot more steam and a cleaner tune up.......
I know you've been messing with nitrous for awhile, notice how the recommended tune ups haven't changed even though everyone knows they are not as good as they should be.
 

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First round fodder...
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3,602 Posts
get some numbers together and post'em. jet sizes,timing, retards, and fuel pressures. looks like fat cond. to me. how fat did the plug read???(the ones not hurt)
 

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Grandpa
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6,479 Posts
Discussion Starter · #16 ·
ok here it is. I was at [email protected] 5.5fp. 30base timing pulling out 15.
I run an 8.50 index class and the car went 8.41.so I did this...
dropped the outers down to 34n30f and the inners to 32n 30f.left everything else the same. next pass the car went [email protected] the plugs on the left side looked alittle rich,but I didnt think it was that rich.I gotta get this POS figured out!LOL!
 

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SOFA KING WHAT?
Joined
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43,675 Posts
ok here it is. I was at [email protected] 5.5fp. 30base timing pulling out 15.
I run an 8.50 index class and the car went 8.41.so I did this...
dropped the outers down to 34n30f and the inners to 32n 30f.left everything else the same. next pass the car went [email protected] the plugs on the left side looked alittle rich,but I didnt think it was that rich.I gotta get this POS figured out!LOL!

Man that's odd. We ran the 18 degree set up in Tom's Chevelle Saturday at Cecil with 34n 32F pulling 12 out from 32 and went 8.11/166, I know the air was funky later in the day, when did it happen?
 

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Vendor
Joined
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6,472 Posts
Man that's odd. We ran the 18 degree set up in Tom's Chevelle Saturday at Cecil with 34n 32F pulling 12 out from 32 and went 8.11/166, I know the air was funky later in the day, when did it happen?
The race before this one at the beginning of month.

Check those jets out and make sure nothing is plugged up and if you can hit them with a pin gauge or something to make sure they are all the same.
 

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"Darkness"
Joined
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4,942 Posts
ok here it is. I was at [email protected] 5.5fp. 30base timing pulling out 15.
I run an 8.50 index class and the car went 8.41.so I did this...
dropped the outers down to 34n30f and the inners to 32n 30f.left everything else the same. next pass the car went [email protected] the plugs on the left side looked alittle rich,but I didnt think it was that rich.I gotta get this POS figured out!LOL!
You picked up ET and MPH after you changed to smaller, staggered jets?

Have you ever tried smaller,leaner tuneups with more jet spread? Those 4 jet spreads run fat no matter what.
 

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The nitrous guy
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7,189 Posts
Too much timing takes straps off plugs. Has nothing to do with the N/F tune usually. Can't see the top of that piston, but likely that happened over time from a rich tune beating on the rings. I would say that you just got lucky and caught it at this point, before it got worse. If it got oil in there and detonated bad enough to take the strap off, the piston would be burned, with alum sprayed everywhere. The heat is what kills the ring lands. Extra fuel washes the cylinders down, the rings get extremely hot, they transfer the heat to the piton, piston starts to fail from excessive heat in the thinnest spot (usually at intake pocket). As piston goes down, it tries to pull the top off, as it comes up, it pinches the second ring. Once the second ring is pinched, oil is sucked in the chamber and you get the burned pistons that everyone sees. The ones with the side torched down to the pin. All this is caused by fuel. I would say you got the above piston before it pinched the second ring. I would also bet all the tension is gone from the rings on that hole. Appears you have 2 issues. A rich tune and too much timing, causing 2 different problems.

Just saw your tune ups. You are extremely rich, especially in the heat of the summer

Monte
 
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