Sealed Power Brand Pistons with DuroShield Skirt Coating

[sandlapper]

From Melling M55 to M155
If you freshen an sbc and plan for a New OE-type Oil Pump --- might I suggest to look beyond the old standby Melling M55 --- Instead, suggest Melling M155.
About late-80s to mid-90s, GM & Melling reengineered (yes Improved) the venerable M55 pump --- their engineering studies revealed by increasing M55 5/8" OD pickup tube to 3/4" --- it improved Low to Mid rpm efficiency & stability --- it seems the overall pump design is great at Pushing oil but somewhat lacking in abilities to Suck oil. Increasing to 3/4" made a notable difference. Hence, all OE from that period thru today's sbc performance & race crates & new powertrain replacements get a standard volume-std pressure M155 with 3/4" OD pickup. If you phone Melling tech and tell them which pan you have, they can and will advise which Melling pickup part number to use with M155 pump. T shirt

 

[tom3]

I assume the coated pistons are designed for wear protection with the new oils used today with much lower barrier lubrication additives?

 

[sandlapper]

Tom, I don't think skirt coatings are so much about oil --- as it is about an ability to fit pistons tighter in bores.
Newer alum alloys have even less expansion --- newer machining processes/capability allows bores to be even rounder and with even less taper And with bore surface finishes which promote better ring seal --- a better bore surface requires less ring tension for seal and a tighter piston rocks less; also improving seal and thus efficiency. The polymer skirt coating is more for scuff prevention in tighter bores. A large portion of motors' wasteful friction is in the ring-to-bore interface --- less ring tension directly results in less friction and increased efficiency. It's all somewhat of a concert with many players.

So far, and in general, alloys that expand less are also more brittle; not a top choice for racers.

Racers use skirt coatings to ammend oil as you suggest; but that's a relatively small segment of the coatings market. While other coatings are used by racers to reflect heat.

 

[FS87LT]

Those coatings were around when we still had "SL" rated oils, with just over 1000ppm of zddp in them and 5W-30 had just become the normal "spec" viscosity motor oil.