'99 twin 7.4 MPI's in a velocity 320. Already has stainless marine exhaust and K&N arrestors. Suggestions on worthwhile upgrades? I realize the internals are cast, don't want to get that deep into the motors. I was curious if these were worth converting to carbs? Would ignition upgrades be useful? Feel free to spend my $. Drives are bravos with hydro Q4's.

I have the same motors and talked to a guy from Merc Racing. He told me I could go 500 HP safely with them by changing cam and heads, ignition, etc. and still retain MPI. Haven't done anything yet as motors are low hours but when I do was planning to contact him for specifics.

Werd--just what I like to hear. Do you have a name who you spoke to? PM me if you'd rather.

I modified a 1995 7.4 carb motor years ago. I changed the heads to rectangular port, changed the cam, intake, and exhaust. The results were spectacular. With the speed increase of the boat I figured I gained about 120 hp.

This was all fine and well until I had a problem. After a hard run when cruising about 3800 rpm I spun the main bearings. It seems I got the oil too hot. The mistake I made was to use the stock oil cooler from the 7.4. It just couldnt keep up with the higher oil temps generated by the modified motor. So be careful. Get an oil temp gauge if you are going to mod the motor and a bigger oil cooler.

Ron

A few years ago I converted my 7.4 MPI to carb , after switching to SM manifolds. No big HP gains, but mid-range torque increase was good.
I eventually broke a rod, so I rebuilt the engine with a stroked crank , big roller cam and added Merlin heads and MSD igniton.

Its a cast engine with an ultra low performance intake. I wouldnt push it too hard. Need long block with better internals.

swap them out for something better! Why dump $$$ into those motors? Is it really worth the time and money?

You may have a good point. I guess I am looking for some of the cheaper (is there such a thing in the marine world?) upgrades to better enhance what is there. I would think that finding a couple used intakes and heads with new cams and ignition upgrades ($4K?) should yield good results for the $. Selling the two motors and purchasing two more would certainly cost 3-4x that, atleast. Am I too optomistic in my thoughts?

What are you looking to accomplish by spending $$ ? Speed? Reliable motors? Fuel economy?

I think I already have reliability and all that can be expected from economy and twins, so I guess speed. I would love for mine to have a stronger sound, maybe a little more lope.