Moly filled vs plain ductile iron top piston ring 2

[Lou Scannon]

I've done some searching, and nothing I found specifically addresses my question. I am rebuilding a factory turbocharged engine that originally came with a chrome faced top piston ring. These rings are no longer available, so my choices are a typical moly-filled top ring, or a traditional non-filled iron top ring. What are the pro's and con's of each, considering that I intend to make use of a great deal of the engine's inherent power capability?

 

[EHudson]

Moly has better scuff resistance than chrome. The only time it may not be the best choice is in very dusty conditions were the dirt may get trapped in the pores of the moly and act as an abrasive. If you have good air filtration or do not operate in dusty off road environments, opt for moly.

Rule of thumb: If the engine makes more than one horsepower per cubic inch, (60 hp/liter), then a nodular (ductile) iron or steel is the best choice as a base ring material - for strength.

The plain iron ring is strictly a low cost option.

 

[Lou Scannon]

Doing a little more searching on the net, I found out that ductile iron rings are relatively new and not to be confused with old-fangled cast iron. My question is, for my application, am I better off with a new style ductile iron ring with no fill, or one with that is moly-faced?

 

[EHudson]

Ductile, also call nodular or spherical graphite iron has been used in piston rings for at least 40 years. Moly has been used as a wear surface on rings for about the same length of time. There is nothing new about either

Get a moly-filled, ductile iron ring.

The ductile iron is stronger and will stand up to pressure better than grey cast iron. The moly is wear resistant and scuff resistant.

 

[Lou Scannon]

Thanks for the info. The latest findings in my web search lead me to the same conclusion. Thanks again!

 

[Tmoose]

basic moly filled rings can lose their moly whjen subjected to detonation. Detonation is pretty much a given in a turbo engine.
Plasma moly has a stronger bond, but it is still weaker than chrome's bond.

 

[Lou Scannon]

Great info! I will be sure to get the plasma sprayed variety of moly rings.