A buddy of mine has a 1993 31ss Sonic w/ carburated 502's and the cast iron manifolds are becoming brittle and flaking away. They're bolted to stock Mercrusier stainless steel elbows, which appear to be in good shape. He's looking to replace the manifolds and elbows w/ stock Mercrusier manifolds and elbows, which are both cast iron w/ ceramic insides. He's also considering Stainless Marine manifolds and elbows. Is there any noticeable performance gains w/ the Stainless Marine vs. the stock? Also why isn't Mercrusier making the cast iron manifolds bolted to stainless steel elbows as replacement options?

As long as he needs exhaust anyway, I would ditch the stock merc exhaust and go aftermarket. The stock merc stuff has been the death of many engines including mine.

Stainless Marine is definitely the way to go.
They weigh 1/2 as much and don't have that wet joint that leaks into your engine over time.
I gain 150-200 rpm over the stock cast stuff.

I just got my stainless marine... and it looks sweet!

Merc stopped offering the SS risers because of the deterioration they cause to the cast-iron manifolds. You'll love the Stainless Marine units.
Lighter, breathe better and look great.

I agree with the others...get the Stainless Marine exhausts if you can. Depending on how many mods you do to the engines the more the aftermarket exhaust like the Stainless Marine will work for you. As Cozzi said, they're much lighter, allows the engine to breath much better, look great and long lasting---you can't lose! Thos estock Merc cast iron manifolds are very heavy, look terrible and are extremely crude in performance. Boat anchors are about all they're good for! Have fun!

I'd check out Revolution Marine at www.revolutionmarine.com They are definately the best value around.

stainless marine,nice upgrade.give us a call,we can help w/ your purchase
954-237-0332

Stainless Marine. However, if he wants to go cheap for right now, I have a good condition exhaust off my 2000 7.4 MPI if they would work. About 250 total hours fresh water only. Got a new motor going in and what's left of the old one will be sold.

I think I read that a Stainles Marine exhaust has never failed and caused engine damage. I've never had them, but that's the route I'll go when I do.