LMM ring gap question

[57ringo]

I'm curious what the guys that build these engine are using for ring end gaps? I've got an 07.5 LMM +.020 bore, stock cam & heads, EFI LIve tuner, EGR delete, 4" exhaust, stage 1 turbo upgrade. I'm using Mahle cast performance piston # 930036075 that comes with rings # S42160.020. LMM +.020 bore, stock cam,heads & injectors, EFI LIve tuner, EGR delete, 4" exhaust, stage 1 stock turbo replacement. This is a cab & chassis with flat bed towing a 32' trailer some of the time. The guy at Mahle said .025" but that would depend on my application. .004"-006" x 4.075" so that could be from .016"-.024" but also I've read where Fingers suggested in another post
"0.012"-0.018" on the top ring. Open up another 0.005" at most for severe hot rodding, but no more. IMO
0.020"-0.025" for the second ring. I prefer to keep this one tight, but philosophies vary here. Keystones seal better with less inter-ring pressure. Or so I am told."
Suggestions?

 

[Fingers]

GM Spec is as you quoted me. 0.012"-0.018"

However, my understanding is the GM rings are cast and the Mahle are steel. (i could be wrong.) They expand differently. With that in mind, I would still shoot for 0.018"-0.020" for the top ring, which puts you in both ranges.

 

[malibu795]

Mahle states theirs should be .004" min per every 1" in diameter .004*4.055=.01622

 

[57ringo]

thanks, Should the second ring be a little more?

 

[Harbin_22]

Mine are around .030 and I have the blowby to prove it :roflmao: But seriously do have a lot of blowby n compared to a stock engine, but I make a lot more power so I'm OK with it

 

[Fingers]

Don't mix Forged specs with cast. Forged rings need more gap. They do not seal as well and have a lot of by-pass regardless of gap and heat up a lot more.

The Keystone design seals much better. As a result, the rings stay much cooler. Add to that the oil gallery helping to keep the rings cool, (BTW that is why the gallery is there) and the Cast specs can be much closer. Even in high performance engines.

 

[melms23]

GM Spec is as you quoted me. 0.012"-0.018"

However, my understanding is the GM rings are cast and the Mahle are steel. (i could be wrong.) They expand differently. With that in mind, I would still shoot for 0.018"-0.020" for the top ring, which puts you in both ranges.

This is how I looked at it when assembling mine. For my application I felt comfortable with .018 - .020"

 

[57ringo]

The rings that came with the pistons are steel.