moly or iron top ring?

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66dartman

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On this 318 bracket engine I am building I am leaning towards an iron top ring sealed power ring set. I know the moly rings last longer, but don't they take longer to seat? This engine will only power the car to the strip and bracket race, so it doesn't have to last 100,000 miles. My planned 4.88 gear swap will kill its highway use!! I am using KB-399 pistons with 57cc chambers for 12:1 compression so it will be a 110 octane motor if that makes any difference.
 
all 3 types are iron rings... the facing is either plain iron, used with a fairly rough hone finish; chrome platied facing for use with a fairly rough surface finish, and molybdenum coated facing for use with very smooth plateau hone finishes. moly seats fastest with the right finish and little lubricant. chrome takes the longest to seat, but lasts the longest. they are all iron rings with different face coatings.
 
More important is what finish did your shop leave? Moly faced rings on a rough finish means the moly gets torn off an the ring becomes plain iron. With moly, it has to be a very fine hone finish. Then, the rings will seat in the first few seconds to the cylinder walls, and the first loaded pulls to the piston ring lands. If the bores are finished with the std hone, something between smooth and what a ball hone or fine hand hone leave, std iron will seat best, but will need the older method of smooth acceleration uinder light load, then decel, then repeat for a few miles. They will continue to seat for the first 500 miles or so. If the bores are rough finished, you can use a chrome facing, but it will take a while to seat. It will wear much longer, but it takes a while (in miles or hours) to really seat. Most ring sealing issues with moly rings are because the wall finish is wrong.
 
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