5/64 piston ring availability and ring gaps?

[RTsehibb]

For those who are using the Speed Pro L2355 forged pistons, or any other original 5/64" ring forged pistons, what ring gaps have you used? 

I posted previously about piston to wall clearance and hopefully this will help others who use the 2355 pistons.  (Thanks again for advice received).   

Speed Pro specs are .004 minimum for a 4" bore size, but I ran into a problem with availability on what seems to be seldom used piston rings as most pistons use the 1/8" rings now.  For a 69 440 Magnum bored .040 over mild build:

I have a finished bore size of 4.363"

Speed Pro L2355F .040 pistons

Sealed Power E-424K40 rings that have a .029" gap in the bores


Minimum ring gaps would be .017 and stock specs are .013 to .023?  Machine shop would like less gap than .029 so a ring set for a .045 over bore file fit down would be needed.  That would be a 4.365 ring size.  (Where I live machine shops are few and far between so I appreciate their attention to detail).

Problem is after searching, no 4.365's are available in the 5/64 size.  Even Total Seal confirmed this but they said for such a large piston ring, a .024 would be the minimum gap and that the .040 oversize rings from Sealed Power should work fine. 

So my question for the engine builders is how big can you go on the 5/64 ring gap on a mostly stock 440 rebuild?  Is .029 too big?  Since you can't file fit down the .060 over rings that are available, is their any other options?

Thanks again guys for your opinions or advice.   

 

[Challenger340]

So you put the Pistons in at .0045" Piston to Wall ?

I know of no .005" over file-fit rings in 5/64" on the 4.360" Bore.

I think given the same application factors as discussed earlier, given the "Heat & Fuel" Load, I would probably being targeting .024" -.026" Ring Gaps anyways to be safe on the large Bore exposure ?
Remember it's the top ring that see's all the heat and "tightens up" it's gap @ combustion temps during operation. The only concern with the 2nd ring is that it doesn't seal better and hold pressure then UN-seating the top ring seal.
And,
with these newer higher silicon 4032 Forgings, while the thermal stability is excellent,(in part because of more rapid heat transfer throughout it's structure), the top ring is still exposed as a heat sink with limited cooling.

So IMO, .029" will run fine.

Yep, if ya had ur druthers..... you may shoot a little lower than .029" ?  .... "maybe" ?     But again here, IMO, it will NOT have excessive blow-by at .029" and it will run just fine.

[RTsehibb]

Thanks Challenger 340, your opinion is what I needed.