hillbilly pony

So that being said for a NA 347 will the .010-.020 (top) .018-.028 (bottom) stock limits be ok??

67mustang302

What does the piston manufacturer say for your application?

hillbilly pony

Keith black calls for .016 top ring.

67mustang302

You want atLEAST the minimum gap. I prefer gapping a bit on the fat side myself, combustion occurs so quickly that you don't lose much power from larger gap, maybe a few hp which doesn't matter much in a street car. Too much gap will live, too little gap won't. ESPECIALLY if you add boost or spray. I'd rather lose 3hp than have ring end butting and broken pistons.

hillbilly pony

Seems like a huge range cause even ford spec is like max of .038. .016 seems small to me. so about .020 would allow for spray in the future safely? KB says manufacturer specs for bottom ring. got any suggestions for a safe range??

tinman

I don't think that .016 is too large.
Old school rule was always .004 per inch of bore.......

hillbilly pony

Does that equation apply to the bottom ring also?? or does it need to be bigger?

tinman

That .018-.020 should work out on the bottom ring OK too....

capri debris

N/A... .018 top and .022 second.

Boost or spray... .020 top and .024 second.

Second ring is ALWAYS supposed to be gapped wider than the topso combustion gases can escape from beween the top and second rings, so the top ring only has pressure on it from the top and not from under it or it won't seal against the cylinder wall properly. Every set of rings I've installed has this recommended in the instructions and it makes sense.