So I've been looking at some boats and found one that I think is under powered. Its a 99 43 BT with 502 MAGs. If I can get the boat at the right price is it worth modifying them to around 500hp. What would need to be done and how reliable would they be. It already has exhaust so nothing needed there. Would a cam swap work with some new valve springs and push rods?

Just trying different options here.

Your only limiting factor is the budget you set.

I figure that just not sure what these motors like.

The stock Merc mag cam is pretty wimpy - especially on the lift side. Merc/GM intentionally went very conservative on the lift and duration because these things were going into everything from cruisers to performance boats to runabouts, and they had to support a warranty. A cam with more lift and duration would work together with your exhaust to get you close to where you want to be. The heads will be the limiting factor to getting much more than that. It might be worth finding a pair of HP500 cams and lifters that were taken out of another motor if you want to stay on a budget. Then match it up with the Dart style single plane and a pair of 800 cfm Holley's, and you will be close to cloning an HP500. If you plan on leaning on the engines at all, upgrading to inconel valves is highly recommended.

i disagree about the exhaust working with a hp500 cam,it will revert big time,also i believe the 502 mpi engine has inconal exhaust valves.

A 43 BT will take some serious power to make go fast. IMO, a cam swap and a few other items, wont do a whole lot for performance in that hull. It might get you 2mph. In this scenario, I would leave the engines alone, and run it and enjoy the reliability of the 502 mag. When youre ready to go fast, sell those engines, and build a pair of engines that will net some gains.

I believe to hit 80 in that hull, you''ll need 750-800HP a side, and 900's to see close to 90, and you'll need some stout drives to take it. A buddy of mine has a 46 with 575sci mercs and XR's. It runs low to mid 70's, and eats bravos.

I think Budman is living up to his name today. The limiting factor is the intake manifold. I do like Buds idea of the Dart style intake and carb though, it would be by far the best bang for the $$$ ( with a cam). IMO, the 502 mag mpi is a great engine to leave stock. I have one I've ran for 13 years and have only done oil changes and plugs. Its really staggering from a cost/time standpoint gaining that extra 5-10 mph. I guess I should take my own advice though as I'm in the middle of a 550 hp build right now!!

http://www.offshoreonly.com/forums/d...e-results.html

I didn't see where he said they were MPI motors - if that is the case I would definitely agree with what MT and lounge said about leaving them stock and enjoying the turn-key reliability. Mike, I'm in agreement with you about the reversion with the HP500 cams - you have to be careful depending on what exhaust is being used. He said exhaust is not an issue, so I took that to mean that he had some kind of performance aftermarket exhaust, but if they are the stock Merc manifolds, then yes, reversion would be an issue. There may even be issue with the Gil manifolds, as Merc had quite a few warranty issues with them. Careful research is in order if s022mag elects to proceed. Probably the best bet would be a pair of take-out performance engines or build a pair, and leave the stock motors as backups or sell them to finance the upgrades.