[GTO]

This fall after I smoked my buddies 33 Dodge Coupe, again, he pulled his tunnel ram 454 BBC because "There's something wrong here!". He was right and I'd like to share this problem and maybe get some of your thoughts. Some of us use Perfect Circle Rings on our Pontiacs so I think this is relative. During cruises he used to go through a quart or so of oil, about ~100 miles. Before he pulled it apart a compression test showed no problems. When he had it apart 6 pistons had broken ring grooves. The funny thing was that the ring grooves were broken upwards. The Tech guy at Ross said that the cause of the failures were the P.C. rings. He said that those pistons could easily handle 250HP NOS. What happens is that the rings seal so good that under NOS they actually create a vacuum in the cylinder which pulls more oil down the valve guide. The oil collects on top of the second ring and because a liquid does not compress it pushes up on the top ring and breaks the ring groove. The grooves were not made to take upward presure. He will be calling Perf. Circle to see what they have to say but for now I would just like to know from some of you guys, "What do you think of this?". Thanks...ERIC V.

[GTO]

This fall after I smoked my buddies 33 Dodge Coupe, again, he pulled his tunnel ram 454 BBC because "There's something wrong here!". He was right and I'd like to share this problem and maybe get some of your thoughts. Some of us use Perfect Circle Rings on our Pontiacs so I think this is relative. During cruises he used to go through a quart or so of oil, about ~100 miles. Before he pulled it apart a compression test showed no problems. When he had it apart 6 pistons had broken ring grooves. The funny thing was that the ring grooves were broken upwards. The Tech guy at Ross said that the cause of the failures were the P.C. rings. He said that those pistons could easily handle 250HP NOS. What happens is that the rings seal so good that under NOS they actually create a vacuum in the cylinder which pulls more oil down the valve guide. The oil collects on top of the second ring and because a liquid does not compress it pushes up on the top ring and breaks the ring groove. The grooves were not made to take upward presure. He will be calling Perf. Circle to see what they have to say but for now I would just like to know from some of you guys, "What do you think of this?". Thanks...ERIC V.

[Scott Misus]

How can a ring seal "Too well?" Isn't it suppposed to create a vacuum? Wouldn't the fault lie in the valve guide and its excessive tolerance?

[PONTIAC DUDE]

First question: 250 HP? if you run the stock ring gap, the rings butted & lifted the piston top. 2nd: Timing, if you don't retard enough it will lift the top of the piston. Compression with octane determine the amount of retard along with cam profile. I don't believe the ring caused the problem w/250 as I've run 400 hp with moly rings & no problems. I've run TRW, Ross, Wiesco, Badger, Silvolite, & Kieth Black with out any problems following the RULES of NOS. I've seen lifted piston tops, but all could be traced to lack of knowledge or misuse. More info needed as in timing & octane, compression to get to the real bottom of the problem. Later, dude.

[LarryF]

Check out the website for KB pistons. There is a lot of good information there that applies regardless of whose piston you are using. They talk about a very small amount of blow-by being useful to keep oil from getting past the oil rings and up into the combustion chamber, but it is really to prevent detonation. This sounds more like one or more of the problems that Pontiac Dude posted.
http://www.kb-silvolite.com/1toc.htm

[GTO]

The only reason we thought that this could be true is that the motor was fresh and it was using oil. The oil consumption problem was not mentioned to the tech guy before he told us his theory. Here's some more info: 3700#, TH400, 3500 stall, 4.56 gears, 29.5 by 10" tire, 12 to 1, Eagle rods, Ported oval ports, tunnel ram, 2 600 Holleys, 2 stage NOS 150HP and 300HP, 6 deg. retard on the 300HP, top ring Gap widened for NOS according to Perf. Circ. specs., CC Mech. roller 264@.050 .651 lift 110 lobe sep. and he ran 114 PRO FUEL at the track. I'll agree that the guy's story sounds a little bizare but he say's they've seen this problem before. He gave my buddy a good price for replacement pistons and told him to stay with a good set of standard, not gapless, rings.THANKS...ERIC V.

[PONTIAC DUDE]

Yo, first off 6 degrees is not enough retard for that compression even with 114. rough formula is 2/3 degrees for every 50hp. this will lift the piston. seen it!! also SP & PC recomendations are to tight. .028/.032 min.& the second one to .018 & it won't use oil if the hone pattern is correct. I also coat the tops for heat dissipation. (mirror finish.) check you intake fit as I've seen oil drawn thru the bottom of the intake at the ports. check your runners. Also dome pistons in a BBC will lift right above the intake relief on the flat side right? flame propagation is very poor with a dome on NOS and the load is all on the area around the reliefs. that's why BBC with a FT and the aluminum 88 cc head is the ticket. Oil in the cylinder with NOS is an accident waiting to happen anyway, so I don't even know why he even tried to spray it. Check intake guides as exh usually won't cotribute to this problem. Hope I help supply some things to look for? Also stay with the regular rings no gapless. there was a good article on the Fastlane NOS board on that subject. see-ya, Later, dude.

[GTO]

Your right about the piston lifting around the intake valve relief! We also only retarded our motors 2 deg. for every 100HP. this will change now. Thanks for all the great advice it's good to have a place where you can get a good second opinion. ERIC V.