you have the GM injection, you need the Mercruiser injection. A friend of mine rebuilt his motor new cam headwork put it on the dyno and barely saw any gains,,, we switched the injection and instant 50 HP before any tweaking or ECU remapping.

The downside is a used injection system sells for over $1,000 used ( I happen to have an extra one here by the way !!! )

 

to much $ for the injection Id switch to the carb first easier to rejet and tweak

 

well its your call,,, but Boat nut and I made the same trip at the same speed,,, he used 50 gallons of gas,, I used 32 !!!!!!!

Besides, buy a carb and mainifold and your close to a grand anyway.

 

good point

 

heres an email I got ,


Russ, the 330 horsepower is measured at the crankshaft, if it was measured
at the propshaft it would be 300 horsepower. Your engine is measured at the
propshaft, 310 horsepower, if your engine was measured at the crankshaft it
would be 340 horsepower. You have one of the best marine engines built, I
really like the cylinder heads and the fuel injection unit. The only
modification I would make to your engine would be the addition of a Gil
exhaust system and remove your camshaft and send it to Comp Cams and have it
reground (much cheaper than buying a new cam) to 212 degrees intake duration
and 218 degrees exhaust duration with a 112 or 113 degree lobe separation
angle (keep as close to the stock valve lift as possible). Call the Comp
Cams 800 number for advice. Install a fuel pressure regulator that will
increase your fuel rail pressure (it is located on the Mercruiser cool
fuel). Changing to an intake manifold and carburetor is the only way to
increase horsepower past 400 without having to mess with the computer. I
have a book I have written called BIG BLOCK CHEVY MARINE PERFORMANCE that I
can sell you for $19.95 ($17.95 + $2.00 ship) send a check to Moore
Performance, PO Box 1413 Monrovia, California 91017 (write BB Chevy Book
on the check and include your phone number)

 

crmax

It depends on what you want to do with your boat. If you are looking to make more power build a carbureted engine. If you are have problems upgrade your current injection. It is less expensive to build power with a carburetor.

Doug

 

thats what I thought now the desision hp or mpg

 

If you want minimal hassle and maximum time-on-water... EFI is the way to go....

better fuel economy too!

 

So what injection do I have on my 2001 MPI 7.4

 

if your flame arrestor is pointing forward you have the same as in the trucks with the 7.4 mpi which is the same as the 310 version for marine I think the truck version puts out 290 horse