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Premium Member
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OK, Iam going to throw myself under the bus here and let everyone know what went wrong with our 300 mi enduro motor. FIRST Iam NOT blaming the piston yet. The piston is a KB Premium Forged deal, #770 with a 1.395 CH, 36cc dome in a 496 tall deck. They are damn nice units with alot of good features if you look at the pics. The one in the motor is not coated like the other in the photo, and probably should have been. It's also had it's exhaust relief cut, exactly like the coated one, although not very much as the photo of the original piston will show. Mainly it was cut at a different angle, with most of the material taken off towards the top of the relief. It burnt thru right where the little bump is, in the underside photo(not the sharpy mark). That in itself seems odd. The exhaust was cut for another build, with a very long @.050, which the coated ones WERE going to go in, but I am waiting until I cut this piston up and see EXACTLY how thick it is there. Motor was conservetivly rich, 38* timing, 110 Sunoco 6300rpm. If they won't take this, even with the cut, they would never going to take what I had planned for them. THE REASON I am posting this is because I like the abuse Iam going to get from you guys hil:) and to let you know if you run these, DON'T CUT EM, and don't spray more than maybe 150. The larger dome pieces seem to be thicker in this area than this perticular part#. When I get it cut up I will let you know what I found, right now I am a little busy getting ready for the Thanksgiving Opener and the Kilo attempts in Dec.



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mo balls than $cents$
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dang! they do look like nice pistons, that's the 1st real pics i've seen of the pistons. please post up the cross section pics, be neat to see.
 

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Cantard
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5,017 Posts
Almost looks like where the hole in the bottom is (pic # 3) matches the spot in the top? Be interesting to see if any of the rest of the piston looks burnt on the bottom.
 

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mo balls than $cents$
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11,734 Posts
It will be a a few weeks, have a blower deal I have to get together and dyno'd before the first week of DEC, for the KILO attempts, and that's the block I am useing, so thje pistons will be coming out before then.
tease:D
 

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www.highflowdynamics.com
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1,161 Posts
So a piston burned a hole, no biggie it happens. Finding the limits of stuff is cool. :) And if you're not breaking parts once in awhile, then you're not pushing/finding the boundaries. Yeah, looks thin from what little info the picture (top view) can show. But don't cut it up; weld it up, reshape and use the set in a milder build. I know of plenty of pistons fixed as such and running strong...unless you are saying that the c/r would be too high regardless of head....hell, whack the dome off too and use 'em in a motor for your truck or sumthin....

LO
 

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Cantard
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5,017 Posts
UMMMM LakesOnly ahhh thats something that happens but never gets talked about.:D Buddy of mine just did that.... piston is still good but the block is broke in 3 pieces now. lmao
 

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grumpy old guy
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181 Posts
i read your post with some intrest because i have had this exact same thing happen years ago when i was running huge gobs of NOS on big inch motors----1 were the edges of the cuts @ exhaust and intake where they overlap or meet smothed over or did they have a sharp edge? it dosen't take much of an edge to start some bad things to happen and belive me being rich does't mean much if it can find a spot to get a hold of also you will probly find that at that spot that the metal is going to be thiner one thing to keep in mind with NOS that the thermal bang in the cylinder WILL find the weakest spot and from there every thing will go away i have been away from the NOS deal for quite some and things always change but back then the best piston combos i found were the weiso t-2000 series pistons for large amounts of bang juice there big things happening inside the combustion chamber when running juice i am just asuming that you are from the way your post reads if not there is still huge things happening in cyl. @ detination i will be watching your post to see what you find with intrest GOOD LUCK :)devil
 

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steelcomp was here
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26,512 Posts
Am I the only one who hates trying to read someone's writing who dosen't use punctuation?:)sphss

GN...all I can see is there wasn't much time spent finishing those pistons after ther pockets were cut. Sharp edges are asking for detonation under those conditions. I'm curious as to the thickness there as well. These are good pistons, but seems even they have their limitations when you start messin with them. That sure looks thin. Looks like maybe that little indent on the underside is your culprit. Ya know, there is a simple tool for measuring dome thickness. :D
The ex pocket looks a lot bigger than 1.88, too.

Lakes, sometimes you amaze me.



 

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300 mi enduro motor.
Motor was conservetivly rich, 38* timing, 110 Sunoco 6300rpm. If they won't take this, even with the cut, they would never going to take what I had planned for them.

How far did it get / how long did it run?

Is it NA?
What type of induction?
Is the 110 Sunoco leaded?

Steve
 

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Lurker
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1,417 Posts
Not knowing what this thing went through, how long it was ran or the thickness of the crown in that spot it is hard to tell what came first. But...I do know that the radius on the fly-cut needs to be about ten times what was used. Even if there was plenty of cross section in this area, all the stress from combustion stops and is concentrated at that corner of that sharp radius. If I was to look at that piston before being installed, I would guess that would be the failure point in the crown if there was one. A huge radius washing into the rest of the crown lets the whole piston absorb the stress and would make a huge differance. Again, if it was too thin in that area nothing would stop it, but if thickness isn't an issue, the flycut is the problem. Not only from a detonation issue (rest of piston top need to be dressed/contoured) but from the concentration of stress I mentioned above.
Been through that in the little NA stuff and FEA supports this thoery.
 

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I had Swain Coatings coat the sides of my pistons. They are about 20 mi. away from me.
Decided not to coat the tops.

What do you guys thing about coatings for the top of pistons?

Jim
 

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I had Swain Coatings coat the sides of my pistons. They are about 20 mi. away from me.
Decided not to coat the tops.

What do you guys thing about coatings for the top of pistons?
Coating the combustion chamber?

Jim
 

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steelcomp was here
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26,512 Posts
Not knowing what this thing went through, how long it was ran or the thickness of the crown in that spot it is hard to tell what came first. But...I do know that the radius on the fly-cut needs to be about ten times what was used. Even if there was plenty of cross section in this area, all the stress from combustion stops and is concentrated at that corner of that sharp radius. If I was to look at that piston before being installed, I would guess that would be the failure point in the crown if there was one. A huge radius washing into the rest of the crown lets the whole piston absorb the stress and would make a huge differance. Again, if it was too thin in that area nothing would stop it, but if thickness isn't an issue, the flycut is the problem. Not only from a detonation issue (rest of piston top need to be dressed/contoured) but from the concentration of stress I mentioned above.
Been through that in the little NA stuff and FEA supports this thoery.
Good eye...looked right past that. Definitely a factor here.
Warp...what's your thought on pocket dia. vs. valve dia?
 

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steelcomp was here
Joined
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26,512 Posts
I had Swain Coatings coat the sides of my pistons. They are about 20 mi. away from me.
Decided not to coat the tops.

What do you guys thing about coatings for the top of pistons?
Coating the combustion chamber?

Jim
It can't hurt. Turbo and high boost apps almost a must for reliability, and reflecting the heat inward instead of it being absorbed is worth power. I did a Buic Stg III V6 Turbo engine years back that made over 1K hp, and even the ex ports were coated.
 
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