1990 7.4 365 HP Magnum
 

I need advice. Wanting to bump the horsepower of this engine up to 500 hp. If I understand right for the bravo one that is about all it will handle.It is a 1990 242 LS with 350 [well maintained] hours. Is this capable with cam,aluminum heads,intake and headers? Rectangle or oval port?? If someone has done anything like this let me know. Or is there a better way to spend the money to acheive this hp??Appreciate any input. Thanks Gus

If you could find a low hour Merc 525 EFI take-out you might be in the same price range (if you sell yours complete) with a much better result, look, dock manners and resale value.

Check the classified's. Someone like BAM Marine could possibly handle the whole deal including arranging for the swap. I expect this could be done in the $15-17k range...maybe with 1 yr warranty. You won't likely get out of you 365 to 500 HP upgrade for significantly less.
Remember, the 525 EFI is more like 540 HP and comes with all the Merc fail safe systems.

Purchase a used 525SC blower setup, and enjoy. There have been some nice deals in the classified, and spam section.




Darrell.

Whats your budget?

Here's one way of doing it----The Merc 365hp is a very good baseline engine...4-bolt mains, forged crank, rods, and pistons and with rectangle port heads. Do a clean-up work in the bowl area of the heads, install some hydraulic roller cams and lifters that will make power up to about 5500rpm, add some roller rocker arms, single plane Dart intake manifold, Holley 750-800cfm carb, and some aftermarket exhaust manifolds such as Stainless Marine or GIL, Dana, or something comparable and you will hit 500hp no problem...with decent docking manners. The key to it all is starting with a better breathing exhaust system as I have already mentioned. Have fun.

Hoping to acheive this around 5k. I will do the labor . Looking at cam heads intake from edelbrock also like the idea of a supercharger. Thanks for the input so far. Will post choices and costs as I recieve them. Anybody locate a supercharger let me know. Thanks again Gus

mrfixxall
 

Freshin yours up and slap a procharger on it, their a little easier on the drive then a roots style blower when planeing out..

Bad,
You will need heads, intake, carb, cam, lifters, pushrods, likely valves, seals, retainers, valve springs, gaskets, exhaust system, misc rigging, flame arrestors, etc. These parts are close to$10,000. There is a lot more to a reliable engine build process than "labor". If you only want to spend $5,000, you won't get to 500 HP. The list of parts that you can re-use is shorter than the list of parts you will need. There is also machine work you may need like: hone the lifter bores, maybe the cylinder walls, cut the heads and cut the intake manifold to fit, etc. All this investment without new bearings? New oil pump and align hone the block?
If your thought is to just bolt on parts to your existing set-up, you won't likely get to 500 HP and the risk of engine failure is high.

When we were starting, we thought about this process just like you....now I know.
A quality engine builder like Eddie or Dean would be the best investment you could make.

Good luck on whatever you decide.

I appreciate the straight shooting from everybody. Now The question is is it worth 15k to satisfy my male ego.Still exploring options. Gus

is there anything wrong with your heads ?
or your bottom end in the motor ?

if you can do the work yourself you can easily make 500hp with that motor, and probably come in under the $5,000 range

Ive had a lot of car motors ( I know boat motors are a little different) and usually the car motors are seeing more top end rpm so theyre making more peak power but 454 inches is not too hard to make 500hp with on pump gas
Ive done a few street motor setups
that have made over 650hp with stock rect. heads, stock bottom ends,

Ive done some that have made over 600hp with large oval heads also with some slight port work done to them, on pump gas and are very mild mannered

its all about setting up the right combination
I would have your heads ported and freshened,
depending on what valves you have possibly go up in size with them (depending on what you have)
possibly even milled depending on what your cc size is to get a little more compression out of the setup if you want
also gotta check what your height your pistons are installed at
the motor I just took apart had the pistons installed .050 in the bore which was killing my compression
so you might have to have the block decked again depending on where your pistons sit right now

go with a custom hyd roller cam from Bob Madera at Marine Kinetics
Good set of valve springs, retainers to match the cam specs
Crane or similar quality hyd roller lifters
correct pushrods
double roller timing chain
new main bearings and rod bearing if you need them
if yours are in good shape re use them
rpm air gap
or single plane intake, depending on what Bob suggests for cam selection
start with an 850 holley carb
new HV oil pump and pickup
possibly even add some ARP rod bolts to your stock rods if you have the extra money
proper ignition setup
and that should easliy see over 500 hp and 500 ft/lbs of tq

that stock magnum bottom end you have is a very good base to work off of and will handle 500hp without anything to worry about
its a good idea to do a leakdown test, compression test on your motor before you start taking everything apart, so it will give you a good idea of what your working with

that should not cost you anywhere near $5,000 if your doing all the checking measuring and assembly yourself

just keep in mind this is all based on if your bottom end and heads are in good shape

if you need anyone to do the head porting and intake manifold porting email me at [email protected]
I can put you in touch with someone local to me who does great porting work,
good luck
let us know what you decide to do

I can help you out in getting close your goals. If your interested just PM me. I can probably even dig up some of the old dyno sheets from 1992.

Looking at B&M 250 Blower with 2 750 carbs. What are the pros and cons with this setup??? Gus

For the HP numbers your looking to produce, there really are no cons to the setup. If it needs to be rebuilt, The Blower Shop Is able to do it. It should be a great package when your done.


Darrell.

Thanks for the input. Gus

you still need a exhaust set up 1st, DEAN GELLNER ENGINES AT 216 398 8500 can get you all the parts needed and stainless marine exhaust a dry set up is 2800 to 3600 for gen 2 or gen3, I have a dry gen 2 for sale for 1200, if I don't trade it saturday. but DEAN can put it together or sell you the right parts. He is one of the best. and stay away from edelbrock heads the dart and afr are way better same money, and intakes to dart single plane is what merc used on the hp 500 with a 800 holley carb. art

It is really not worth investing 15k in a 15k boat. The boat will still be worth about 15k.

I do think you could get by with 10k though if you find some good deals on quality used stuff. You would probably be better off buying another complete engine and keeping your stock one in storage. Reinstall the stock engine when its time to sell.

I didn't think of that, Great idea, theres a lot of motors in the classifeds for under 10,000 and 500 plus hp. and yah he can use the 365hp as a back up or when he sells the boat sell it with the 365hp. I am doing that this spring going to sell my boat minus the 509 no power or but a stock 454 in it.

Keep in mind that you may need external Hyd steering if your speed is approaching the 70mph range.

Missed the two blowers Mike had on a couple weeks ago,but landed the two from MTG Motorsports. Should be here in about a week. I appreciate all the input. Keep it coming,I need all the help I can get. Thanks Again Gus

Finally have a B&M 250 dual carb blower in my shop and ready to start. I have located a v-6 module to help with idle. I want any input that will be helpful on installation,maintenance,anything to protect the engine ( gauges,electronic sensors) ,etc.Appreciate all the information so far. It has been very helpful to this point.Water is still up in this area may get to water test if all goes smooth. Thanks Gus

What is your overall plan????? I would at least change the head gaskets to Cometics or Felpro Marine's. Might as well get a valve job too.

Hoping to gain about 10 mph. Switch back to stock upon resale.What type of valve job? Want to protect the motor as much as possible, egt gauge,etc. I appreciate any suggestions. Thanks Gus

Have a valve job done on the heads while they are off and you are changing the head gaskets.

Have you done this kind of stuff before??????
Do you know how to read spark plugs??????

Ok on the valve job will do. Have done motor work in the past,small block only. If reading the spark plugs means the fuel mixture lean or rich by coloration no. I would appreciate nothing being left to chance.I will not take any suggestions or instructions as implications that I am not knowledgable. I really do not want to trash my motor by doing something stupid,so please give me all your suggestions. Thanks Gus