Piston ring end gap ?

[biosehnsucht]

Any recommendations on setting the piston ring end gap? I've seen various things on the 'net such as 0.004" per 1" diameter OR that and 80% of that on 2nd ring and manuf. recommendation for 3rd ring.

small gap makes for better sealing and more power but bigger is safer to reduce chances of binding as it heats up and expands.

at 84mm = 3.307" that would be 0.013" gap or rounding up to nearest size I think my feeler gauge has would be 0.014" (err on side of safety).

Does this sound good ? I know most have just had shops build their motors or used pregapped/OEM rings, but a few of you I'm sure have done it the hard way... I'm leaning towards 0.014" myself, certainly would seem silly to go smaller since it WILL expand as it WILL be pushed

[float_6969]

I can ask my machine shop on Monday what they are gapping my rings at. Mine was SUPPOSED to be 84mm, but CP screwed up and only made them an 83.5mm. They said they'd get me the right ones if I wanted, but I'd have to wait another 2-3 weeks and then have the block bored and honed AGAIN. So I just told them to send me the correct rings...

[biosehnsucht]

Well, ended up gapping the top rings to ~0.019" and the middle to ~0.025"... didn't gap the 3rd rings, they were all about the same and the FSM specs show such a wide range of tolerances as to not matter..

First reason for these gaps is that no matter which cylinders we put the rings in, we got 0.019 on 3 and 0.015 on the other, so we widened up the 0.015 to 0.019; then for the 2nd ring we had 0.006, 0.008, 0.025, and 0.007, or something to that effect.. so we widened up the other 3 to match.

Now, this might seem big, but looking at the FSM 0.025 is JUST within OEM specs, and being I'm overbored that widens the gap some more. Also, I saw a few places on the web saying 0.04" per 1" bore and 80% of that on 2nd ring, but OE specs make the 2nd ring bigger and a page on Federal-Mogul's website recommends doing the same, they also have a list of recommended bore-gap ratios, and for supercharger and nitrous street (nothing for turbo) they recommend 0.0055 - 0.0065 for the 2nd ring, so we figured being boosted, high RPM, and etc better to go w/ the 0.025 we already had to work with..

[float_6969]

My shop gapped them the other way. The 1st had more gap than the 2nd. I was also supprised at the amount of gap that they were supposed to have. I thought it was a much more narrow opening. But the guy doing the work has a Pro-Stock drag car that's got a 2 stage nitrous with well over 1000hp he built, so I've got faith in their engine building abilities!