obrien24

iTrader: (2)

I am looking at building this combo to install into a boat. My goal is to keep the revs under 6000 if possible, but I am trying to make 550 to 600 crank hp, and 550 tq. I am looking for suggestions on a cam for this engine. Also, will the stock head to the job, or should I look for head that has been ported?
I have the components to make this engine fuel injected using the MEFI 4 ECM, but I am not opposed to going to a carb.
Any other suggestions would be appreciated.

Schwanke Engines

iTrader: (1)

Well, you would need to have the heads and intake ported if you want to make that HP level. I think the Mefi will work just fine, you would need to get one you could tune on, I believe AZ speed and marine is the only option for boats. I think you are going to find you will make more TQ than HP with this setup due to the cylinder heads. You could get it to go the other way around with LS7 heads, but then you are talking big bucks.
Why don't you give me a call and we can get something put together for you that should get you to your goals.

obrien24

iTrader: (2)

Having more tq will certainly not be a problem. I was looking into arizona speed and marine, but they have closed down. I have found the software that will allow me to tune the Mefi, or I could go to innovation marine engines and have them work on the tune ( it will just be expensive). Innovation actually did the marinization on the stock LQ9 that I have. What do you think I will be looking at for a cam in this combo?

I have your number, and I will see if I can give you a call in the next couple of days.

AmericanMuscle8.1

What size/kind of boat and what drive/gear ratio are you planning to run?

I think your going to run into a few problems. First is if your boat has any hull or weight to it at all, it's going to take some torque to get it on plane. If you pick a heads/cam setup that doesn't build torque until over 3000rpm, your going to sit and wait on it to plane (if it can). If it has a real strong top end to it, it's going struggle until it planes off and then be all over the rev-limiter on the top end. Use a Mercury Racing 525 as an example. That's a 502ci EFI NA motor that builds close to 550 crankshaft horsepower @ 5200rpm. Even building peak horsepower that low in the powerband, its torque curve is still pretty soft under 3000rpm and still struggles to get larger boats on plane (look at any performance tests out there). Not knocking that engine at all, it's awesome, but if 502ci making 550hp @ 5200rpm has trouble getting boats on plane, a 416ci engine making similar horsepower at an even higher rpm is going to have a hard time getting a boat up out of the water.

Crusader builds a 375hp LQ9 6.0L that has awesome performance. 5400rpm redline and great acceleration. Unfortunately they only build it for an inboard, but with some a bellhousing and coupler swapping there's no reason it couldn't push a sterndrive boat.

Last thing... I think you will have a hard time keeping an engine together running it over 5400rpm. Oil temps will climb, possibly oil foaming issues, and you will have sustained high loads on everything in the motor. You will also need closed cooling because you don't want to pump lake water through aluminum heads or an aluminum block.

Just my 2 cents from a marine engine guy.

obrien24

iTrader: (2)

The boat is just over 22', and I am not sure yet on weight, since I am going to be changing things a bit. I will be running a bravo 1 1.5 ratio. This engine was already set up in a boat, so I have CMI headers and tail pipes, race mount, and closed cooling system for it. If I was running in fresh water, the closed cooling woundn't be needed but in salt I will def. need it. The engine was in a 24' Cigarette and ran about 72 mph but it was turning up around 6200. This engine was completely stock internally as it came from GM, and only had the exhuast, closed cooling, and MEFI 4 efi added to it for marine use. Innovation Marine said the engine made 422 hp on the dyno. Now I have torn it down to the short block for now since I plan on building it bigger to help make the extra tq that I will need to get it up and running. You also have to realize, that most boats are not even on plane until they are over 2000 rpms and they are struggling at that point. Granted that can very quite a bit with so many different applications.

The engine also has an oil cooler so that will help with the oil temps, and I plan on beefing up the valvetrain a bit to handle higher rpms for longer periods of time.
I am planning to build this engine to handle the revs, but it won't be there for long periods of time. No more than propbably a minute. I am not one to hang it out for too long.


As a far as the 525 engine goes, yes it is a great engine just like the previous 500's. What you have to realize though about the larger boats getting on plane, is that they are usually running a tall gear ratio with high pitched props for top end speeds. A good example would be the 36' Cats that I used to build for Spectre Power boats. This boat with the 500 EFI or 525 usually ran a 1.36 ratio with atleast a 34" prop. That was good for 110 mph in most applications, we even had one boat with some custom 36" props that ran 116 mph.
Thanks for the input.

Schwanke Engines

iTrader: (1)

here is a LS3 headed 440 in a boat down in New Zealand,
The video is quite large, but it is worth watching. There are 2 more links on our home page under the title, Brian Direen - New Zealand Boat Videos.

Enjoy