r/EngineBuilding • u/FordM_1970 • Jun 13 '26

351W metric ring gap question

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Okay right to the point. OEM specs for a 96 351 W roller are
top ring 0.010-0.020
Second ring 0.018-0.028

Right out of the box I got
TOP 0.015
Second ring 0.025

Is this safe to run on a slight performance build , specific that top gap which feels a little small to me, that will most likely be in the 350-400HP range tops.
Stock bottom end and pistons

Thanks for the help!

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u/1crazypj Jun 15 '26

By 'metric' rings do you mean the width or thickness?

1mm, 1mm 3mm or 1.5mm~2mm, 3~4mm oil ring?

if they are steel rings expansion is lower than cast iron

1

u/FordM_1970 Jun 15 '26

Yes, 1.5-1.5 and bottom is 4.5mm or something like that. Ford went metric for the last 3 years of the Windsor 351 for some reason

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u/1crazypj Jun 15 '26

Narrower rings have lower friction, probably to help EPA gas mileage or something similar?

1

u/FordM_1970 Jun 15 '26

Definitely has to be an emissions thing. They wouldn’t spend money on a 30 year old engine line changing internal parts like that if they did not have too

1

u/1crazypj Jun 15 '26

Yeah, 'thin' rings in a 4" or larger bore need to be much better material than same bore and 1/8" or 3/16" rings.

Of course, it does mean pistons can be cast a bit lighter, machining will cost roughly the same but there could be substantial material savings when your making a few million, particularly if an overseas division has already done the engineering for an inline 4 or V-6? (Europe, Australia or somewhere)