496 ho Exhaust Replacement

[Goldeneyee]

I just purchased a very low hour 2003 Donzi with twin 496 ho motors that had been in indoor storage for 5 years. It appears that salt water in the aluminum exhaust manifolds on the port engine has corroded through the area around the brass water nipple/hose area. The starboard set may not be far behind. It looks like manifold replacement time. Should I replace with Mercruiser and where could I find the best pricing; Or, upgrade to a competing brand of exhaust or headers. Would I gain any horsepower/speed with aftermarket exhaust and would they be compatible with the ho computer setup? The boat will be run in fresh water. Thanks... Bill

[Carl C]

You can find lots of pull-offs from suckers who bought CMIs. Very few people report a speed increase with CMIs on a stock 496HO so don't get suckered in by the phony claims in Powerboat. They are $5,000 bling. If you don't believe me then do a search on OSO.

[MOP]

I have heard several reports of the brass fittings rotting the Merc setups, anyone that has a set with the brass should change the fittings to S/S.

[oledawg]

Sounds like good advice to me!

[Goldeneyee]

Mop: The boat I purchased has 32 hours on the engines and was stored inside a building for the last 6 years. The port engine's exhaust manifolds are shot with a hole directly adjacent to that brass fitting. I should take a pic and send to Merc and let them ponder that for a while.... Bill

[MOP]

It boils down to Chinese brass is cheaper then Chinese S/S! It is like the elimination of the grease fittings on the gimble assy, they save on machining and fittings. We pay the price of planned obsolescence one of my main gripes with Merc, most other manufacturers strive for a decent product.

[Noble]

I put lightning headers on a 288 sunsation earlier this year and saw about a 1-1.5mph gain. The best part about it was the sound!

[flying tomato]

I have a set of glm exhaust manifolds that I will sell for 250.oo. They are 1 year old and are in excellent condition.

Flying Tomato, Lee

[Goldeneyee]

Thanks much for the responses. Has anyone on this board replaced their stock Mercruiser exhaust manifolds on a 496 Ho with aftermarket headers and realized any substantial performance gains? I know Dana and others claim high horsepower/torque gains. Thanks..... Bill

[mrfixxall]

Dont waste the money on cmi's unless you plan on going over 600 hp,a standard performance exhaust manifold is all you need with a ss riser..

Some use stainless marine, some use eddiemarine,..they are good units and for the price you cant go wrong..

http://www.eddiemarine.com/store/cart.php?m=product_detail&p=13693&c=63

http://www.stainlessmarine.com/index.html

[undertaker]

Thanks much for the responses. Has anyone on this board replaced their stock Mercruiser exhaust manifolds on a 496 Ho with aftermarket headers and realized any substantial performance gains? I know Dana and others claim high horsepower/torque gains. Thanks..... Bill


I put Dana headers on my 496HO did not see much of a gain...maybe a little more midrange.....they are less expensive tham CMI's.......AND they are nice bling....good luck:cool!:


Undertaker