I'm running 365hp mags... I'm thinking of upgrading my exhaust. I've been told I don't need to replace the manifolds but to just upgrade the risers. Has anybody done this... did you notice any difference?
I'd like a nice set of stainless steel risers to bolt on my stock Merc manifolds... does anybody offer a reasonably priced product to accomplish this... or do I need to bite the bullet and upgrade both the manifolds and risers?
Thanks in advance.

C M I $1995.00

I'm pretty sure the primary runner design of the cast iron Merc exhaust manifold's are not near as good as Stainless Marine or a GIL aftermarket exhaust manifold. Simply bolting on some stainless pipes will look A LOT better and sound better, but as far as performance goes it won't do much. I prefer something like the Stainless Marine exhaust manifolds with one piece stainless steel tailpipes that go all the way through the transom. They will probably increase your RPM by as much as 200-300rpm and maybe 15-20 additional horsepower on your stock 365hp engines. You might see 1-2mph gain IF ANY on top---you also might see a little better performance in the mid range/cruise as well. But they look much nicer and dress up the engines a bit and they're lighter and sound much better. Then if you choose to add or upgrade your engines with a better cam or port the heads, etc. then your engines will be more sensitive to these mods because of the better breathing aftermarket exhausts that you already have and they will perform well for you. Hope that helps---have fun!

Someone else might chime in hear and add some thought to it as well.

One time I put GIL 6" risers on stock merc manis and picked up about maybe 25-50 rpm. It sounded alot better, but there was very little gain on a 300 454. The only reason I did it was the Gil Manis were going on the new motor and I jsut felt like seeing what would happen with a riser swap.

Not worth the $$ if that is the only upgrade you are making to the exhaust. I really like my Gil set up and it lost a little power on the dyno but picked up 8 ft lbs tq (not my set, a freind of mines).

I agree with the guys above. Don't waste your money on just stainless risers. Get a good set of aftermarket manifolds and risers.

Thanks again guys,
I've done some research... a set of stainless risers from IMCO go for about $800 a set.
Eddie Marine offers their standard "thunder" system for about $1200 (manifolds and risers, not polished)...
This is probably a case of "you get what you pay for".
I bought a boat with with carbed mags, and with HP500 intakes... stock carbs and exhaust. I'm looking to compliment the intakes with a better flowing exhaust and carburetors... exhaust seems like the first logical step.

Check out Stainless Marine. Just put two sets on my uncle's 454. Great product and excellent service.

Check out these guys. Polished are about $1200 per set.Revolution Marine

Team V,

Buy an exhaust system that has a one piece stainless steel tailpipe that has a rounded elbow like a Stainless Marine or GIL comes with. You do NOT want to buy an aftermarket tailpipe set up that has sharp turns or 90* angles----that's what Merc has on their stock risers so why buy an aftermarket exhaust system that has the same type of riser???? Those 90* sharp turn risers slow the exhaust flow down and cause the engine to be ROBBED of power---and that's not what you want! You want the tailpipe exhaust flow to go as easy as possible as it takes a turn in a different direction---SMOOOTHLY. Stainless Marine, GIL or CMI are set up this way.

Again, I would take a good look at the Stainless Marine exhaust system. They are reasonably priced too.

If you go with a true header, you'll see almost a 30hp gain. If you were looking to a cheaper alterntive to the cmi elbow tops (an excellent choice) I'd recommend the lightnings.