Ringland breaking at intake relief
#1
Junior Member
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Join Date: May 2003
Posts: 2
Ringland breaking at intake relief
I have a 4.155 bore 393cid 18-degree SBC. Heavy (42 pill in fogger) NOS. I put about 10 nitrous runs on engine and it started smoking. Pulled head expecting damage from lean NOS tune up, but found the pistons in various stages of damage, looks as though the ring land is flexing and breaking at perimeter where it is thinned for the intake relief. It has a 2.20 valve so it really crowds the edge. What can be done to prevent this from happening? Rings are dropped .29 inches from face, gas ported JE flat tops. Need help, I'm afraid it will ruin another $$$ pistone set.
#3
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Join Date: Dec 2005
Location: Rutherfordton North Carolina
Posts: 192
Send the pistons to Swain Technology and have them ceramic coated on top,this really helps pistons that are thin in the valve pocket area.we do this with all our N20 and turbo engines.Bill
#4
Senior Member
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Join Date: Mar 2007
Location: mich
Posts: 208
mmitchel, how long are the rods 6"? to get 393 you most be running a 3.630 stroke with the 4.155 bore? you problem isn't heat related right? the piston isn't melted at the ring land right? if the piston isn't melted and the problem isn't cause by heat then coating the pistons is a wast that will not fix the problem. move the ring pack down ..050-.060 more and that should do it. the oil ring will need a support rail but from my math it should have one now. the coating a good idea for some safety margain from a missed tune up but wont fix the ring land being to thin at the edge. the extra .050-.060 will give you a piston that is .350 down from your .290. good luck with it
#5
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Join Date: Mar 2004
Location: Maine,USA
Posts: 1,204
Originally Posted by billhendren
Send the pistons to Swain Technology and have them ceramic coated on top,this really helps pistons that are thin in the valve pocket area.we do this with all our N20 and turbo engines.Bill
Valve size, 2.200
Piston relief,is cut deeper to accept the 18 degree valve,which inturn means a lesser distance to the 1st ring land.
Nitrous means more heat on the top of the piston,coating I believe will help.Also oil sprayers from the connecting rods will help cool the bottom of the piston.
Do your home work on a better ring stack on the piston.
All piston qualitys are not all alike,different type grades of aluminum alloys.
And I am prolly forgetting more but thats off the top of my head,maybe this will bring more to the discussion.
Gas port the piston to get a better ring seal.
Use a good hell fire ring with plenty of ring gap= atleast .007 to the inch
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#7
Member
MASTER JOURNEYMAN
Join Date: Apr 2003
Posts: 48
Re: Ringland breaking at intake relief
Originally Posted by mmitchell
I have a 4.155 bore 393cid 18-degree SBC. Heavy (42 pill in fogger) NOS. I put about 10 nitrous runs on engine and it started smoking. Pulled head expecting damage from lean NOS tune up, but found the pistons in various stages of damage, looks as though the ring land is flexing and breaking at perimeter where it is thinned for the intake relief. It has a 2.20 valve so it really crowds the edge. What can be done to prevent this from happening? Rings are dropped .29 inches from face, gas ported JE flat tops. Need help, I'm afraid it will ruin another $$$ pistone set.