sorrento454

I´ve a sea ray 25 sorrento and exchanged the engine from a 454 (330hp) to 7,4LMPI and the engine have less power and consume more fuel! Do anybody have similar experiences with the engine? Any suggestions what to do?

East Coast B

I wouldn't think you would see any difference between these two engines when it comes to the power. The 330hp is actually 300 at the prop and the mpi is 310 at the prop. How much speed did you loose, did anything else change? Are you hitting the correct rpm range of 4200-4600rpm? Was engine properly installed and aligned?

Again, I don't think you shouuld see any difference in performance.

SeaRay Jim

Another Searay here. I wouldn't think you'd see/feel any difference either.

You could always do what I did and retire the 7.4 MPI.

Searayously, did you change anything else, drive, props, change exhaust etc.?

sorrento454

I had alpha (1:1,36) with 15" prop. Max speed was then 37 knots. When I changed engine the alpha was replaced with bravo1 (1:1,5). I know that the bravo will slow the boat a slightly but the difference is too big in my opinion.
With 17" prop the max speed is 33,5 knots at max rev 4200.
With 19" prop the max speed is exactly the same and max rev 3950.
The mpi engine seems very week compared to the old engine.
I´ve measured compression and that´s ok on all cylinders.

East Coast B

As you go up in prop pitch, your revs will come down as you've stated.

How heavy is your boat? I'm not familiar with your model. Still, being a 25 it can't be that heavy, unless it's a cruiserI would think a 17 or 19 would be banging your rev limiter.

Use this site for calculations http://go-fast.com/Prop_Slip_Calculator.htm
Plugging in your information, your running a high rate of prop slippage.

You should be running up to 4600 rpm with that motor, with that said, a 15" prop will give you 2-400 more rpm. Can't believe this should be the solution to your problem though. I definitely feel that motor isn't putting out the HP it should be.

Can't reiterate enough though that you shouldn't be seeing any difference in power with that motor compared to what you had in there.

Did you or a shop put the new engine and drive into the boat? New or used engine? Seems like your losing power somwhere, all cylinders firing? Engine aligned properly? Getting enough fuel?
I've had a 95 300hp carb 454 3200lb boat/mid 60's mph and a 98 454mpi 310hp 4600lb boat/upper 50's and I couldn't tell any difference between the two powerwise.

East Coast B

Just saw a pic of a sorrento.... it is a cruiser.... explains the slippage rate... You have a sport boat drive on a cruiser which is the reason you are finding the lower pitch props are working better. A bravo 3 /2.0 gear ratio would have been the hookup for that boat. My buddy has a 26 sundancer 2000 and the 7.4 310hp with bravo 3/ 2.0 and he's running about 44 with it. And that's fully loaded with all kind of extra weight, he carry's everything with him. Your pushing a lot of weight with 3 blades which is causing the large slippage rate.

With not being familiar with cruiser setups, only input I can give for your current setup is to try out some 4 blade props, they can do wonders for heavier boats without the bravo 3 drive. The 4 blades will decrease your slippage rate changing some of it into speed. Try props until you get to 4400-4600 rpm.

Good luck!!!