I'am looking at purchasing a pair of factory Mercruiser aluminum Exhaust with riser pipes.Are they any good ? I'am looking at making about 450-500 H.P.What would they be worth?Are these any different than the old cast iron stock exhaust other than they are aluminum?Any help would be appreciated.

If they have the center riser they have better flow than the logs.

The aluminum will save you some weight too.

An alternative option is the Dennis Moore GLM reproductions on ebay etc.

They are pretty cheap and most folks have had good luck with them.
They are called exact replacements but they are more like "suitable" replacements than exact. They are much cheaper than stock merc.
They are supposed to yield a slight performance gain.

Although my experience with Dennis was less than ideal, (caught him on a bad day maybe?) some folks have had decent results.

Are you talking about the Merc/Gil exhaust like these???? I think they are the only aluminum Merc manifolds.

Yes,these are the ones that say Mercruiser on the sides and the are made out of aluminum

They are made by gil for mercruiser, they will be fine for 500+ hp. I just got a set for my buddys boat to replace his cracked gils.

The GLMs are available in aluminum also.

They are not a stock merc part.

They are a reproduction.

Don't forget Revolution cast manifolds, I think they are better than the GLM units becuse they are a dry joint between the manifold and the riser and I think Revolutiion sells them for about $900 complete painted and about $300 more for polished. We have made 600HP with them on a N/A motor. Just another suggestion.

Ray @ Raylar

They get my vote also, good quality, dry joint and an unbeatable price. Put them on my buddies 560HP BBC 3 years ago, still looking good. They also have all the brackets to relocate the stock accessories that are mounted to the mercruiser exhausts available.