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So I'm putting together a 6.0L LQ9. I'm reusing the factory hypereutectic pistons. I re-honed the cylinders so I bought new rings. I got a Hastings ring set with a plasma moly steel top ring and a ductile iron 2nd ring. I'm trying to gap these and the Hastings gap chart seems way bigger than any other info I can find on the internet. I understand that you need a little more gap with a hyper piston as apposed to a forged or cast, but this seems a little high to me. I'm running a 150 to 200 shot of nitrous on this motor. This is the chart right off there site.
So I have a 4.000 bore. That means they are recommending a 0.034" top ring gap and a 0.026" second ring gap. That seems very large on the top ring, Also I thought the 2nd ring gap was supposed to be larger than the top ring? Anyone have any incite? And yes I know nitrous can be hard on plasma moly rings. But being that this is a Holley controlled progressive shot on a street car the chances of detonation are very low. The tech at Hastings recommended these rings for my application once I told him how the nitrous will be controlled. But he also told me to look at this chart for my ring gap.
Last edited by Phobos84; Apr 21, 2021 at 06:59 PM.
No expert here, maybe call the manufacturer and double check.. But IMO that sounds way too large. A lot of ring packs are Moly uppers and I don't think I have ever heard of anyone running a gap like that on stock LS pistons. Even guys with drag only setups and/or pushing a lot of boost only go to about .030" on the top ring.
No expert here, maybe call the manufacturer and double check.. But IMO that sounds way too large. A lot of ring packs are Moly uppers and I don't think I have ever heard of anyone running a gap like that on stock LS pistons. Even guys with drag only setups and/or pushing a lot of boost only go to about .030" on the top ring.
Well I didn't call but I emailed them today. This guy told me to set the top and bottom ring to 0.030 for a 150 shot of nitrous. More if I was going to go with a 200 shot. I might try a different brand.
As the guys before mentioned its the piston makeup and amount of nitrous thats setting your end gap. Hyper pistons with their high silicone content really put a lot of heat into the upper ring. It may sound larger than normal but when its up to running temp. they will close up.
Well I guess I feel better about using these rings. Do you guys think I need that much gap being that the shot is progressive? It will only be at a 200 shot for a real short time. Most of the time it would be way less being that the shot changes with rpm.
Thanks guys for the advice.
Last edited by Phobos84; Apr 21, 2021 at 09:00 PM.
It’s a double edge blade. w/o the juice big gap loses compression BUT with juice it closes up a lot. If the rings end gaps butt together and close up it’s all over. The cost of running the juice.
I posted this same question over on the LS1tech forum. A member there sent me an insert from a GM service manual for the LQ9.
(service manual LQ9).
Piston Rings
Piston Ring End Gap - First Compression Ring - Measured in Cylinder Bore - Production 0.31-0.52 mm 0.012-0.02 in
Piston Ring End Gap - First Compression Ring - Measured in Cylinder Bore - Service 0.31-0.59 mm 0.0122-0.023 in
Piston Ring End Gap - Second Compression Ring - Measured in Cylinder Bore - Production 0.51-0.77 mm 0.02-0.03 in
Piston Ring End Gap - Second Compression Ring - Measured in Cylinder Bore - Service 0.51-0.84 mm 0.02-0.033 in
So my understanding is the "Production" section is for when the engine was new from the factory. The "Service" section is for if a GM tech does a rebuild. So on a rebuild the upper limit on a stock engine is 0.023" for the top ring and 0.030 for the second ring. So I guess me going to 0.034 on the top ring and 0.026 on the bottom isn't that bad. This is the first build I have ever done with hyper pistons. Everything else has been forged either in cars or ATV's so gaps this big are new to me.
Those rings gaps aren't too far off for what I use with pump gas and high boost. I typically set my ring gaps around 0.075 - 0.08 x bore for boost on pump gas with stock pistons.
I went 0.09 x bore for my last high boost pump gas build and it survived on 93 octane at 30 PSI and I never had any blow-by issues.
Odd ring gap question
