242ss upgrade to 500HP

[DWeiss67]

I have a 1990 242 ss with a stock 454 @ 330Hp LH rotation and a mirage 21 pitch prop. It has a Bravo 1 Drive, 1.50 gear ratio and @ WOT 4600RPM's she will do 50mph by GPS. I’ am going to work this engine this winter. I don’t think it has ever been out of the boat, she only has 1052 hrs on it and I can tell the risers are starting to go so who knows what else is eaten through.

Once I have it out and broken down if the block is good, does anybody know of any marine packages to buy or should I just piece meal it as I go? I've been on EBay but that stuff seems generic. I want to keep it normally aspirated, not to much room under the engine cover as it is. I would also like to use aluminum as much as possible to lower the weight of this beast; however, I live @ the Jersey shore and we are in and out of the salt water but it is always flushed out do you think that route is more trouble then its worth?

Any Ideas would be appreciated; this is my first boat rebuild so I am looking for a starting point and as much HP as practical.

 

[aquaforce]

The sky is the limit ;D ;D ;D


Speed cost money so how fast do you want to go ;D ;D
How about that for rhetroic ;D ;D


I am in the home streach of almost the same thing. My 242SS is an 87 and it started with an Alpha but I changed it to Bravo drive. My gear ratio is 1:36 and for that reason I am stroking my 454 1/4 inch. The added torque should make the plane time and acceleration just like stock with 1:50 gear, and a LOT more top end. ;D ;D
Many boaters here are running aluminum heads. In fresh water there is not to much concern with corrosion but the salt is different. Running aluminum in salt can survive by avid flushing or the best thing to do is buy heads that are marinized or you can have it done. The difference of marinized or not, is having the coolant passages bronzed or ceramic coated to prevent corrosion problems. It works very well for all around performance, weight and longevity. The stock intake on my 454 mag HO is aluminum and merc never had it coated. Surprised me but it has lived in both fresh and salt for about 620 hrs.

You will definately need to re-cam the engine. My 330 hp 454 had oval port heads and intake which are a major power killer. You need better heads and intake both to make power with that setup. Making those changes the current cam profile would be a limitation and therefore need to change it. Yep your looking at a whole sale change out of most of your engine parts.

One easier way to do this is buy a merc HP500. Much faster, easier and a lot less work. It just so happens that a member here has one for sale.
CUDA has one that I considered. I opted out for a stroker setup but if you want a good merc engine that would save you time and money, you could IM cuda and buy his. He has a very good price on it. Then you could sell your engine and put it towards a quicker solution and I garantee you it would be cheaper. Plus you will have to change carburetion and prop and drive shower (if your not already running one) and, and, and, ;D so you will need money for that too

I am installing a 4 1/4 stroker kit to make mine a 496 and I am several thousand dollars out already. Yea it will be a sweet payoff but it takes a lot of time and $$$$$ this way. I went with proComp aluminum heads with 2.250 stainless intakes and roller valve train. We are expecting 555HP at 650 torque ;D ;D ;D The dyno will tell all 8)

I have been unshrouding, porting and matching my heads up all day today. Not going to finish one head all this weekend. Bummer.

Do you have pics?
Good luck on your project

 

[t500hps]

To make 500HP the only good parts you can re-use are the block and accessories......crank, rods, pistons, heads all need to be upgraded.

 

[aquaforce]

To make 500HP the only good parts you can re-use are the block and accessories......crank, rods, pistons, heads all need to be upgraded.

That is just about it in a nut shell.


Also...If you use parts like a forged steel crank that is the internal balanced design then you will have to buy a different balancer pulley. The stock pulley is for external balance. Then the flywheel either has to be machined and balanced for internal or replace it. Either way it is money.

 

[DWeiss67]

Thanks for the info guys. I thought it would have to be a total overhaul. I know aluminium is gonna be a problem but I think the weight savings will out way the negative aspect with the salt water. I thought about buying a crate engine that allready puts out 500hp and that might be an option down the road when I get it out of the boat and see what condition the block is in. For now this is mainly a winer project you have to have something to do.

I would like to see 70mph if possible the only concern that I have is the engine cover, if I put in a manifold that rises to high I will not have the space for the crab to fit without major retrofitting the lid to accommodate it. I put some of that space bed foam on top of the crab and closed the lid to get the shape and spacing and man there is not much room for anything let alone a bigger crab. Has anyone come up with a solution other then cutting and reglassing the lid?

I would like to keep this project at around $8000 I only paid $15000 for the boat so it hard to turn a good deal into a money pit, the boat is very reliable in its current setup and in great shape. I would like to try to keep it that way, at least as much as possible. Its no fun sitting dead in the yard, but then again 50 is lame too.

 

[aquaforce]

The room under the cover would fit a late model 496HO believe it or not. I have measured it by mercs install specs. There is a thread here about it. The risers I think would rise up behind the seat back and clear but I haven't put my engine in to check that part yet. Some room for a close fit can be gained by shimming up the cover where it sets down. Probably not room for a super charger but I'm staying NA.

Merc also remanufactures the 454HO which is available as a 383HP fuel injected engine. That 383 is prop hp and not engine hp. Depending on where that hp number is measured makes about 30 to 40 hp calculation change in prop speeds which would be 2 at most 3mph difference. If you ever look in the classified section of offshoreonly.com you can see prices on this package. It would run your boat at least 62mph. Not a bad option for the money.

If you build yourself $8k would get you the power your after. That would be parts and machining alone. If you pay for good forged parts and have it assembled for you then you could spend $15k pretty fast.

It is workable ;D

 

[Mopower]

A friend with a 242ls cloned an HP500 for his. Now .030 over (509 cu in) and 535 hp. 24" Bravo @5300 GPS's at 69.99999999mph Speedo is a little more optimistic :