I'm building a budget 350-400hp 355cid. I know that moly rings are better, however are they worth the extra money? What is the downside to cast rings versus moly?

Cast is what it says. Cast. Brittle maybe in contrast to moly.

Nuthin wrong with cast rings, I've put lots of em in engines
bach when. I remember when moly rings started coming on, people said they took a long time to break in. Nawww, they do ok too.

http://engineparts.com/p_lv_pistonrings.asp


You are budgeting this one tight, what's the price difference in moly vs cast?

Moly rings need to have a good finish hone with deck plate to seat quickly. Seal better and last longer than cast once they are seated.

Larger Dave

Street = cast.
Racing = moly.

I already have a set of new cast rings, but I think a new set of moly rings is around $40 (not much in the scheme of things, but still $40 that could be spent else where). I'll probably end up with cast but just wanted to ask opinions since its my first time to build a short block.

hey 40 bucks is 40 bucks. I wouldn't be afraid to run them.

When I worked in a engine shop back in the early 80s I was surprised to see Chevrolet was using a moly filled top rings with a cast 2nd ring back to at least 1966 (maybe much earlier) in all their gas powered V8s. If cost conscious GM thought the moly top ring route were worth a few extra bucks at the very least so should you. Having said that, cast ring will work ok but I never found them to last as long as a up graded moly top ring set.

It is a lot cheaper to spend 40$ now than prematuely tear it apart to rering it later.

I've built more 200-350hp cast piston/cast ring motors than I care to remember, and have never, ever, ever had a ring seal or durability issue with them. IMO they are much more forgiving of a less than perfect cylinder wall finish than any moly ring I have ever used.

At our shop we use all moly rings but we plate hone all our blocks as the moly ring is considered a premium ring over a cast ring.

But being a budget rebuild I am sure it was not plate honed and we consider that job substandard machine work compared to what we do at our shop.

On engines we have had on the dyno that was not plate showed a big big differance as far as extreme blowby over a plate honed block. And we see the numbers as far as torque and HP seem to be down as well.

Here is a good link to look over
http://www.camaros.net/forums/showthread.php?t=58964

Building a budget engine...that include boring/honing new pistons etc?
Go molly everytime....that extra $40 is best spent there in the long run
or just a quick hone as the bores are in tollerance?
Go cast.