I have been thinking about changing exhaust manifolds on my engines since I am doing complete rebuilds on both of them. My question is would changing over to the merc 496 manifolds be worth the money? The boat is 38ft and 15000 lbs. not a go fast just a cruiser. the max rpm is around 4800 and will not see that very often, just wanting to make them a little more efficient. What manifold should I use? the stock Mercruiser , the aluminum would be nice to take a few hundred pounds off the stern. Any suggestion would be a great help. I realize the stock Mercruiser chokes the hell out of the engines. Thanks to all Jamie

I use the Mercuriser aluminum 496 exhaust on almost all my BBC's. You will drop about 40lbs per manifold and riser alone and every motor likes better exhaust. You just have to come up with a place to mount your oil filter remote like I did.
I used a couple pieces of L angle and just reverser it.

I'm lucky on the oil filter, mine has a mount that bolts off of the bellhousing

I need a little schooling on the 496 exhaust manifolds , what is involved in installing the merc 496 manifolds on a 454 with the old style exhaust and 4in risers. I'm not worried about the exit or mufflers etc. I will figure that out later, I just want to know if there is any mods I have to do before I change them other than inlarge the bolt holes. What about the plumbing? my boat is fresh water cooled , I have seen 496 manifolds with water rail and with water rail conversions. I have no idea what all this is because I have never seen one in person. Will some tell me the differences in the 496 manifolds please.. Thanks guys Jamie