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iTrader: (7)

I am running Diamond pistons and their rings in my LS6 383. The tech's at Diamond were basicly useless when I asked them how they wanted their own rings gapped. I have a 3.905 bore. Talking to a local engine builder he told me I needed to gap the second ring smaller than the top. I want to run a TNT 150-200 shot of nitrous on this engine in the future. I went with the standard .0045 per inch for the top ring and .0035 for the second ring. So they are gapped a hair over .018" on the top ring and .014" on the second ring. Now talking to another local engine builder, he is saying the second ring needs to be wider then the top. So what is what. I have read engine builds in the mags going both ways. I don't want to tear this engine down and regap the second ring but I will if I have to. I have had no problems so far but I don't want the rings to butt up on the bottle.

briannutter

having the 2nd ring smaller than the top went out 15 years ago. At a minimum the 2nd ring needs to be .002 bigger, many go .004, some of the top teams will go a well over .010 bigger (believe it or not). The compression ring only seals as long as the pressure is above it. What DOES get by the top needs to get by the 2nd as well to keep a buildup of pressure between the two from lifting the top ring. The best pistons also incorporate a pressure seal groove (accumulator groove) to allow more room before the top ring unseats.. -Brian Nutter-Wiseco Piston

Pray

iTrader: (7)

Thanks Brian. So in your opinion, is it worth it to pull the pistons out and re-gap the second ring? If I do, I should just add .002-.004 over the gap in the top ring? Will the lifting of the top ring cause blow by and oil consumption? Is the .0045 per inch gap on the top ring a good size if I want to run nitrous? Sorry for all the questions but alot of people I have asked want to keep the info to them selves. They just want to build the short block instead of tell me what I want to know.

briannutter

Give 'em a bit of a break. It's so easy to look like a dumb *** on the internet, most people won't contribute. Internet geeks that don't build motors will call you out if you don't fully explain yourself. It's just that I don't care

If it's still out of the car, yes..I'd re-do it. Your .0045 top is ok for a 250 shot with some break in before spraying, .0055 for a 300 shot with some break in. but I'd go .006 per inch if you're going "straight to the track on 300+ spray" with no break in. Yes go .002-.004 bigger on the 2nd. Yes, when the top ring lifts, the charge gets by, and the crankcase becomes pressurized..which can increase oil consumption (in other cylinders on other strokes) if not vented properly.

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iTrader: (7)

Thanks again Brian. I hope you don't think I was calling you out on any thing. I just know my limitations. So I go to the experts. I wasn't refering to any one on the net either. I was talking about the local engine building gurus around here.

I have been getting alot of crank case pressure but when I do a leak down test the all the cylinders come back 0%. So I would assume under power is when I am getting the lift and blow by. The engine has about 3,500 miles on it right now. I am swapping to a 408 and giving this engine to a friend of mine. He is a bottle junkie. I want to give him the best engine I can. So when I pull it out I will re-gap the second ring. I think he is only going to spray a 150 shot that I know of.

Brett

briannutter

Don't worry, my bit about posting was meant to explain why people who know don't often bother to post anymore.

That's the problem with static leak down numbers... anybody without access to a blowby meter doesn't have a way of deciphering truth from fiction when it comes to rings.

I'm not that familiar with Diamond's rings and certainly won't speak ill of them because of that reason. I think you ought to throw a new set in though that are gapped as we spoke. Use a diamond tipped nylon brush to clean the bores..Wiseco has them available if you can't find them locally. I've used most brands of rings out there and, when in doubt about an engines oil control problem, I'll go back to a standard tension conventional gap ring and call it a day. It's not the absolute most powerful setup, but it's performs admirably.

STOCK1090

iTrader: (1)

If it is going to get a steady diet of juice check the piston pin to piston clearance when you have it apart. Turbos and nitrious engines heat up the piston quickly and can cause the pin bore to grab the pin. .001 should do maybe a touch more if he will be using a big juice kit.

Check that leakdown meter. 0%???


Rich

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iTrader: (7)

That is good advice. I think pin clearance was .001-.0015 if I remember correctly.

I would roll the engine untill the valves were closed and I added air with my leak down guage. There was no air escaping any where. It didn't register in the guage and I couldn't hear any out the exhaust, intake, or going into the motor. That is how I got 0%

racer7088

Yes you can run even more. Next time you tear your oem GM engine down look at what the ring gaps really are. GM even runs more on the second gap and they are gapped larger than they say in their own specs. The more gap you run on the second ring the more the top ring seals usually and the drier the engine is as far as oil in the chambers as well. I would re-gap the seconds to at least .004 bigger than the tops. As brian says some pro teams like running a much larger second gap.

Pray

iTrader: (7)

Thanks Erik. From what I hear and read you are the man when it comes to engines. It looks like a tear down is in order. Do you agree with Brian on just buying new rings and doing the diamond brushing of the cylinders? I don't want to start any thing between the two of you. I just want confermation. Thanks.

Brett

racer7088

Brian probably just wants a new surface for the rings to mate to and to make sure the cylinders and their hone job are clean. This makes it an even surer thing that the rings will seal up great. I would also guess Brian is talking about the Sunnen PHT brushes? If it were in my shop I would run it through the hone for a touch up as well. Also even on a freshen you have to use the TQ plates if you are using a rigid hone like the Sunnen or Rottler stuff.

I would probably think you could use the same Diamond rings you have and just regap that second ring larger though unless you are having any other problems. I run bigger gaps then some to stay safe with any power adders. This way we never have problems with rings butting up under extreme usage. I am friends with Brian and he really knows his stuff so I don't really have any disagreements with him at all. I just want my pistons faster Brian! hahahahaha!

gametech

iTrader: (1)

I am NO ring expert, but I do know a few things about testing. That 0% leakdown statement scares me. There is no such thing as 0% leakdown on a motor, so there must be a problem with the testing equipment or operator.

racer7088

yeah obviously it goes without saying that regular rings will not return a 0% leak down number! I forgot about that too but you are right that it makes no sense.

Pray

iTrader: (7)

Thanks again for the advice guys. It is probably a combination of both operator and equipment. I have the summit leak down tester. It has never worked correctly. As soon as you hook it up both gages loose pressure. I thought the one on the left was your constant pressure and the one on the right was your leak down %. What I did was set both gages to 100psi. I pluged it in and the air would fill the cylinder, then the pressure from the tank would bring both gages back up to 100psi that they were set on to begin with. That is the only way I could do it with this jacked up gage. I just firgured since both gages read what they did before and I couldn't hear any air escaping there was no leak down which confused me too. II need a new gage.

Pray

iTrader: (7)

I just had the heads off last week and the cylinders looked pretty good. The engine has 3,500 miles on it now. It just put down 497/457rw in 91* heat on Saturday. So it is working okay but there was alot of smoke comming out of the breathers. That is why I think I am getting blow by and ring float.