their is a easier way to go fi,,not coast guard approved YET tho..you will just have to find a way to mount the o2 sensor..

http://www.professional-products.com/EFI_3.php

I've seen mass flo systems work very well in cars. However, I'd be very careful in applying that to boats, completely different animal with completely different fuel to air requirements. Check to make sure they have done performance boats first.

MoTeC, or if thats too spendy, Haltech.

No O2 sensors needed, because it never needs to go closed loop and can run off the base map.

Run a crank trigger, cam sensor (in the old distributor or aftermarket), a TPS and a MAP sensor.

No need for mass air flow sensors or any of that other stuff.

Been doing it on race cars for a long time with MoTeC M800 ECU, but MoTeC now has a new M84 ECU for a fraction of the price.

Simple stuff.

I'm old enough to remember when everyone with race cars and street performance cars were afraid of EFI too. But Carbs can't even come close to a good EFI system for throttle response, cold or hot starting, and fuel economy.

And a well controlled AFR doesn't hurt when trying to make HP either.

well if anybody wants to do this I have a complete(less flame arrester) merc EFI setup, on running boat, everything, from wiring, intake, lines etc...$650 Rob

The problem with most of these systems is they require an O2 sensor. Water will kill an O2 sensor faster then anything. You can do a closed loop system, but be ready to spend a lot of time tuning. There are a lot of ECU's out there that will do the job. You can even use a GM ECU with EFILive or HPTuners software to build your own. Heck I even considered a Mega Squirt build your own ECU. The problem with a closed loop build your own system, is you need to create a base map to get the engine running without hurting it. When I priced out the pieces and parts, I found out I was better off going with an ACCEL DFI system. At least with this system you can find base maps to download to get you close to what you need. In the end you will still give up horsepower to a carb. The atomized fuel can cool the intake charge 20 degrees making it more dense, thus more power. Before you do anything, at least look at the Pro-Systems SV1 carb it has a totally different venturi system that gets you the throttle response you get out of EFI and isn't as sensitive to high overlap cams at idle. All I know is, if I had any more throttle response then I have now with my BG 850 I'd be breaking drives everytime I hit the throttle.

After my quick post yesterday I called Mass Flow and talked to a very knowledgeable man named Sean. They do make a version for marine application that does not have an O2 sensor. They claim to have improved low end torque along with great improvement on fuel consumption. I am planning on going ahead and getting two of these systems. One thing to remember is that the manifolds they use are not marine - brass water passages so I will be buying and sending to them the new Holley EFI manifolds #9901-211 and the matching Holley fuel rails for them to use with their system.

Cliff

Hey Cliff, noticed in your other thread you are running early 80's 330HP motors.

I know this doesnt pertain to your initial question, but here are my thoughts.

According to mass flows website (just took a quick glance) and it looks as if their big block system is 3,000 dollars give or take. That puts you at 6,000 dollars just in your fuel system. in my opinion, and please dont be offended, but you are throwing away a ton of money if you go this route VS what results you will get out of it.

Now, what i would do, is either pull your engines and sell them complete for say 4-5k dollars. Take that 6k you are gonna spend on this efi system, and put that plus what you get for your motors, towards a pair of low hour takeout 502 or 454 MPI magnums. You will go from 330HP mills, to either 385HP or 415HP EFI engines, with much stronger forged internals. Your engines have cast cranks, cast pistons, weak rods.

Good Luck, MT

If those #'s are correct, I couldn't agree more.

How about a used Mercury EFI setup? Replace the harness and Computer with GM speed density setup? The distributor and sensors are GM and will plug right in. You will need to add the O2 sensor to the exhaust.

This would probably be the most cost effective Conversion.
I did this with my Donzi engine.

Jeff

I don't mean to highjack this thread but it pertains to exactly what I am doing with my boat right now. I have an 89 with twin 330hp 7.4's and one of them is blown. I got a great deal on a pair of Gen V MPI 330 with low hours (1 has a lower end knock) so I was planning to replace my 1 motor in my boat with one of the good motors I bought. I was going to convert the Gen IV in my boat to MPI with the bolt on's from the spare motor. From what I've seen I will have to replace the heads on the Gen IV with the newer style heads because of the carb choke heater? Other than that the blocks should be about the same correct? I also read a little that I will need specific head gaskets for the cooling system?
Anyone have experience with this?