Mercruiser 350 Mag MPI Towsports Engine HP Upgrade

"I have an '04 Centurion S

"I have an '04 Centurion Ski boat with the 315hp 350 Mag MPI Towsports engine and the standard 1:1 Velvet drive inboard transmission. My question is ... are there any performance upgrades that can be done to this engine to bring the HP up to the 330hp to 350hp levels? Can the ECM be reprogrammed or tuned to increase power or are there any Mercruiser or aftermarket performance parts that would increase power?

I'm not looking to go faster, the boat will do 45 ~ 48mph as is, I just want more power for pulling.

My current prop is an Acme 12 X 11.5 three blade Nibral unit.

TIA,
Steve"

"Cheapest thing to do is get t

"Cheapest thing to do is get the prop pitched down about one inch, or put on a prop with less pitch. This will give you better low end pull, as it will let the engine get higher up in its RPM band from a dead stop, which means more torque.
Ideally you want to have 3000-3500 RPM almost as soon as you drop the throttle from a dead stop. If you are bogging along for the first 40-50 feet at less than 3000 RPM, you are not getting your best pulling power.

315hp (crank) is pretty much tops for the 350 MPI.
You could put in a 6.2L (383) MAG MPI which is rated at 350 crank hp, but the cost would be substantial. Its the same block so there would be no weight difference.
Otherwise you would need to swap out to a 496 or a 502 big block. Forget the 454.

You could also consider a Whipple or ProCharger add on supercharger system. Whipple make a nice bolt on unit for the 350/6.2 engine which they claim will add 40% power, with minimal weight gain. You will need to get your ECM reflashed also.
The nice thing about a Whipple is that it is a positive displacement belt driven blower, which means that you get boost at any RPM; not just WOT like some systems. This is great for tow sport power making. You can check out blowers at CP Performance. They have a website.
Just some thoughts.
Rod"

"I was looking at the spec dif

"I was looking at the spec differences between the Tow Sports Black Scorpion 5.7 330hp and the 350 Mag MPI 315hp. On paper, it looks like the major differences are the intake systems and the throttle body diameters. The Black Scorpion uses a tunnel ram intake with a 90mm throttle body and the 350 Mag uses a two-piece, long runner type intake with a 75mm throttle body. Both run on 87 octane gas, so I'm assuming the compression and valve train are the same.

Any idea if the Black Scorpion intake and throttle body are available thru a Mercruiser dealer or aftermarket?

I'm guessing that extra 15hp would be fairly expensive? The blower idea would be pretty cool, but I'd be concerned about the long-term durability of the engine with such a system. I'm guessing they're pretty spendy as well."

"I am not sure, but the Black

"I am not sure, but the Black Scorpion may also use larger valves. The cam may also be more agressive with higher or longer lifts.
Both the 5.7 and 6.2 use 1.94/1.50 valves.
I think you are right about the CR; both will be about 9.3 to 1.

Unfortunately Merc don't publish dyno curves for their engines, so it is impossible to tell if the Black Scorpion would give you enough extra torque at mid range to even be worth the bother.

If you had to order all the parts from Merc the bill would scare you silly I bet. You may find what you need on ebay. Someone out there may have blown one up and replaced it with a big block.

You may find someone out there who could reflash your ECM module to squeak out a few extra foot pounds. I have had my Jimmy, Sierra and my Harley all reflashed, and the results have been impressive in all cases.

Rod"