1995 Sport Nautique Throttle Body vs Multiport EFI

[pbarwick]

I have read about the numerous problems with the TBI on this site, but nobody has converted to the Multiport EFI from the Throttle body. I was told by PCM that I have the GT-40 heads, so a lower and upper intake manifold with rails, injectors, and a new ECC should be all it takes correct? I do not understand the difficulty in the Multi-port upgrade vs the carburated down-grade, except for cost. I live in Wisconsin, where the EFI positives are very nice to have in cold weather and in fuel efficiency. Has anyone done this conversion from Throttle Body to Multiport? If so, please send me links, docs, whatever you can to help. Also the exhaust system in the 1996 Sport Nautique routes different I see which helps with the smaller clam shell for the engine and extra storage behind shell. Does anyone know how to switch exhaust linkage to newer design? I love my boat, I just want it better. Thanks a ton in advance. Ski ya later.
PCM says my engine is a 285 horse EFI 5.8L. Others on this site have a 300 Horse EFI 5.8 with throttle body. Is PCM incorrect?

[Mikeski]

RE: 1995 Sport Nautique Throttle Body vs Multiport EFI

Carbs worked great in our boats for 30 years, FI for the past 10 years. My money would go to a nice carb. Swithing to multiport will probably cost between $2-3k versus a carb's $200-400 cost. That cost difference buys lots of gas. If set up correctly the only major difference I would see is having to give the throttle a pump before the first start in the morning. To change the motor cover you will need to change the muffler to the 96 style, I considered it doing it on my 95 but decided it was not worth the cost and trouble.

[darrel409]

RE: 1995 Sport Nautique Throttle Body vs Multiport EFI

My buddy who has a 99SN w/ MultiPort FI GT40 drove my 95SN w/ Carbed Pro Boss. He told me my boat felt like it had more power out of the hole, more top end, quicker throttle response. I couldnt get him out of the driver seat this weekend. 13 years and 600 hrs on my motor never a carb adjustment or issue...knock on wood.
Horse power numbers vary depending on who is being quoted, PCM, CC... plus some are "at prop" others are measured "at crank"... Its just a number. I've heard that the TBI, tuned well, will out run the carb and multiport fuelly motors.
Have you had problems w/ your TBI set up?

[DavidF]

RE: 1995 Sport Nautique Throttle Body vs Multiport EFI

Sure, you can make the switch. But, I was told by PCM that a properly running TBI engine with the GT-40 heads make more power than the GT-40 multi-port injected engines. I think the main reason is that the TBI engines move 950 cfm of air as the mult-port engines move considerably less. Fuel consumption is an issue with the TBI engines.

[pbarwick]

RE: 1995 Sport Nautique Throttle Body vs Multiport EFI

The engine gave me some minor trouble the last time I had boat out, after starting and running cold it maxed out about 33 mph and was running rough, like it was not firing on all cylinders or had a clogged fuel line. A little while later it was running fine. I assumed it was due to the engine not being fully warmed up, but afterwards that didn't make sense because I let it warm up on boat launch first. I have picture of engine I will try to post after I read how. Thanks guys for your feedback.
I want to do engine work for fun, so I was thinking on how to upgrade what I have without complete rebuild. On summit racing I found the intake manifolds and on Holley I found the Fuel injection system. I was thinking about increasing horsepower to the mid 300's with increased airflow and fuel. The marine engine vs non-marine scares me a little however and I can't find any docs to say this is a bad or good thing to do with the fuel system. Fuel injection is much safer, but what marine pieces do I need etc?
Sorry for all of the questions, this site has been a wonderful reference for all of my questions.

[westlake17]

Before you do anything else, get the TBI Manual from Skidim, part# L190140, $10.00. When I bought my -94 with TBI, it was running like crap. After studying the manual I managed to adjust the fuelpressure, and the throttle position sensor. Now I would not want to trade in the TBI for a carb, or even a MPI! I think Skidim also can supply most of the parts for the TBI, like the fuelregulator diaphragm, IAC-valve, injectors, MAP-sensors and so on. In my opinion the TBI is not as bad as people say! Adjust the TBI properly, and keep it!

[Fast351]

Short runner setups like TBI usually work better at higher load than long runner setups like the port injected Ford manifolds. Reason is the short runners flow more (considerably more) at high flow.

This is why, in drag racing, the carbs generally outrun the fuel injected cars. The long runners on the fuel injected motors work great on the street, where they have much better torque. But once it got to balls to the wall high horsepower WOT performance, tough to beat a carb manifold with short 4" runners.

For marine applications where you're running higher RPM constant load, short runner manifolds (whether carbed or fuel injected) tend to work better.

[bobchris]

theres a lot more to change than just the intake, you'll need a new wiring harness and need a new ECM made for a MPI application and all of the other little things too.

[pbarwick]

The holley setup comes with the wire hareness and the ECM and some nice laptop software to program the ECM. I like the idea about the TBI manual submitted above. I will check that out.
Thanks again.

[DavidF]

Holley makes a marine version of their 4V-950 cfm TBI setup. The PCM TBI factory unit was manufactured by Holley with a customized ECM (to work in conjunction with Protec) for PCM.