Engine Swap, EFI or Not??

[dlktdr]

This is my first post here so hello everyone...

I recently just bought a 89 SeaSwirl boat with the 351W engine in it, OMC cobra leg. The bellows were shot and had ruined the gimbal, u joints and both oil seals. I have replaced all these parts over the last few days and all looks good now.

I have a roller, fuel injected, HO 302 engine in a old van sitting in my backyard which runs great. The 351 isn't running so great and risers had been replaced and I wonder if the old ones were letting water in. I was thinking about swapping the two engines come this winter. I know the motor mounts and exhaust manifolds should just drop right in there but I am new to the world of fuel injection. Can I simply disconnect the computer from the van and hook it up or would I need a special computer made for marine use.

The other thing I thought about is just getting rid of the 302's intake & fuel injection and going to a carburetor.

What do you guys think? Also where would you install the O2 sensor on this kind of boat. Or should I just forget it and rebuild the 351 I have?

 

[beermunk]

Re: Engine Swap, EFI or Not??

This is my first post here so hello everyone...

I recently just bought a 89 SeaSwirl boat with the 351W engine in it. The bellows were shot and had ruined the gimbal, u joints and both oil seals. I have replaced all these parts over the last few days and all looks good now.

I have a roller, fuel injected, HO 302 engine in a old van sitting in my backyard which runs great. The 351 isn't running so great and risers had been replaced and I wonder if the old ones were letting water in. I was thinking about swapping the two engines come this winter. I know the motor mounts and exhaust manifolds should just drop right in there but I am new to the world of fuel injection. Can I simply disconnect the computer from the van and hook it up or would I need a special computer made for marine use.

The other thing I thought about is just getting rid of the 302's intake & fuel injection and going to a carburetor.

What do you guys think? Also where would you install the O2 sensor on this kind of boat. Or should I just forget it and rebuild the 351 I have?

Be prepared for the answers you get, most if not all will consist of "rebuild your current block."

This is because your marine engine is made for exactly it's purpose - to run near or at WOT constantly. Your automobile engine was made to run at 1/3 throttle most of it's life. Then take in consideration trying to swap out a closed coolant system for a seawater system. Next is the electrical, spark arrestors and everything else that defines a marine engine and you have a lot of money and a lot of time for not a lot of gain.

Rebuild your 351 or if you have the means, buy a new marine block of your choice.

 

[dlktdr]

Re: Engine Swap, EFI or Not??

Yeah that makes sense, what is any different in the marine block 351 from a standard automotive block? I am no expert at this, I thought they were the same as automotive blocks except for the exhaust manifolds, output couplings and the coolant system, and a few explosion proof components like the starter. But most of this stuff I thought will attach directly to a 302 block.

I'm sure your right rebuilding the 351 block is going to be a lot cheaper and easier for little gain to no gain, just curious more than anything.

 

[beermunk]

Re: Engine Swap, EFI or Not??

Yeah that makes sense, what is any different in the marine block 351 from a standard automotive block? I am no expert at this, I thought they were the same as automotive blocks except for the exhaust manifolds, output couplings and the coolant system, and a few explosion proof components like the starter. But most of this stuff I thought will attach directly to a 302 block.

I'm sure your right rebuilding the 351 block is going to be a lot cheaper and easier for little gain to no gain, just curious more than anything.

I believe you are right, if you are talking about the physical piece of iron that is the engine block. Should be the exact same. Everything else though in the marine is built to a higher, tighter standard because they get revved high for extended periods of time.

 

[bruceb58]

Re: Engine Swap, EFI or Not??

First off, the only things different between the two engines will be the casting plugs and possibly the head gasket and even the cam. You would not want to use the fuel injection system becuase of many issues besides just the safety issue.

The fact that you are replacing a 351 with a 302 would be puzzling to me. Why would you want to go down in engine size?

 

[dlktdr]

Re: Engine Swap, EFI or Not??

Safety issue with EFI, what makes it less safe than a carb?

 

[gadget73]

Re: Engine Swap, EFI or Not??

Also, trucks and vans did not get an HO 302. Its the 5.0 truck engine, which is similar to an HO, but with a different cam. I also would not replace a 351 with a 302 though.

 

[bruceb58]

Re: Engine Swap, EFI or Not??

Safety issue with EFI, what makes it less safe than a carb?

It is an automotive fuel injection and not a marine type.

 

[ryendube]

Re: Engine Swap, EFI or Not??

It is an automotive fuel injection and not a marine type.

whats the difference? what features do the marine system have that makes it safer.

 

[Roman S]

Re: Engine Swap, EFI or Not??

The saftey features of a marine EFI are many. I have a new 350 with EFI. It works wonderfully. However, it has special fuel pump cut outs; the fuel pump will automatically shut of after ten seconds if the engine does not start. My system is returnless, but many require a return fuel line to the fuel tank. The hoses and lines are also marine grade.
RS

 

[Bondo]

Re: Engine Swap, EFI or Not??

whats the difference? what features do the marine system have that makes it safer.

Ayuh,... Mostly the Wiring,+ the Fuel Management program, in the different 'puter...

 

[ryendube]

Re: Engine Swap, EFI or Not??

Ayuh,... Mostly the Wiring,+ the Fuel Management program, in the different 'puter...

ikn components are for the most part sealed due to moisture and lack of ventalation for fumes (ya who keeps the blower on) I guess that could be the reason for the above mentioned cut out or it could be a clear flood mode thing /shrug

 

[Honest Don]

Re: Engine Swap, EFI or Not??

A quick note here. All automotive efi's have a fuel pump PRIME ONLY on start up. after the engine starts, then it runs constant. when the engine stops, so does the fuel pump. To run EFI effectively you'll need an 02 sensor which is extremely difficult unless you have a SBC merc motor, or atleast manifolds, then you just get the adapter plate. The return line is plumbed to the filler hose for the fuel tank, and is done with a piece of 1 1/2, 1 3/4, or 2" pipe with a fitting (Mine is brazed on to ensure a tight seal) coming off to tie your return line into. This is pretty much the norm, and CP performance even sells one version. The fuel pump needs to be for an eFI motor to support to 40+psi fuel pressure, and will need to be external. These tend to run in the $150- $400 range.

I have a holley stealth ram attop a SBC. I simply cut a slice in the floor to drop the braided -6 return line through, then put another floor over it. I did have to fab a lot of things, but it works flawlessly, and the difference is night and day compared to the 650 holley and performer rpm intake from last season. There's no stumble, no warm up, no flooding out, it's simply turn the key and go. The off idle acceleration is absolutely ridiculous, and forget about the midrange. Motor easily revs to 6k, and is very comfortable at 5k.

Another thing to consider is that EFI will actually be safer than a carb because the fuel is incapable of venting into the bilge as it is sealed in the fuel system until injected into the cylinders. If you pop the hatch on my boat, there is never a gas odor- EVER!

Any questions on Swapping to efi and making it work, let me know. I researched this to death and learned alot in the mean time. It's not a project for the timid, but it can be done and is well worth it!

 

[Ole Sarge]

Re: Engine Swap, EFI or Not??

Any questions on Swapping to efi and making it work, let me know. I researched this to death and learned alot in the mean time. It's not a project for the timid, but it can be done and is well worth it!

I want to know everything! I recently did a 88-92 Chevy TBI conversion on my 71 Scout II rock crawler, it runs AWESOME! Huge difference. Some questions to get this started. What system did you use? MPFI, sequential, or what? I assume you just dropped the GM small cap HEI dizzy with 8 pin connector in... What ECM did you use? Do you have wiring or pin diagrams for it? My understanding is that MPFI doesn't really make that big of a difference over Throttle Body Injection. The huge jump is in sequential injection. My big question is how did you work the O2 sensor. I read something about an adaptor plate? How about knock sensor, map sensor, etc. Just mounted on the manifold like mother GM did it? That ought to get this discussion started in the right direction.

Thanks in advance for the info.

 

[Honest Don]

Re: Engine Swap, EFI or Not??

The system I used was a Holley Stealth Ram MPI. It comes complete with the commander 950 fully programmable and tunable computer, as well as an external fuel pump. The set up new is pricey, but I founf this little gem on craigslist for $1k.

From what I was told the difference is definitely noticable between TBI and MPI, but I don't know cuz i tossed the TBI set up i had when I scored the Holley.

I did use the small cap GM dizzy, and the commander 950 has the spark control to go along with it. The map sensor, as of right now, is just kinda hangin there... it'll get screwed to something soon.

As for the O2, you can buy and adapter plate on ebay for less than a $100 delivered. It simply bolts in between the riser and manifold. It's a pass through design to allow your cooling system to work properly, but I have block off plates and a custom built fresh water cooling system.

I also read in a forum some where last year where a guy drilled and tapped an exhaust port on one of his manifolds. O2 sensors like heat to work, but I'm not sure how well it would work because the computer is calibrated with a read and response time relative to the distance the sensor is from the exhaus ports.

Keep in mind also that you don't need an O2 sensor. You only need it to run in closed loop which will give you a more accurate fuel mix at lower rpms, while maintaining optimal fuel economy. After about 2/3rds throttle you should always be in open loop to ensure you never go lean and burn the motor.

I took everything off the motor that i could and mounted it to an aluminum plate bolted to the transom. The aluminum plate because I use it as a central grounding point kind like you car... less wires this way and much cleaner. Plus the thing is just bad *** to look at, and who would wanna clutter it up with solenoids and brackets????

The computer is mounted in a water tight electrical enclosure I picked up at Home Depot for $22. I used a boot from a used door we had at work to seal the harness to the enclosure. The wiring for the alternator I ran under the motor, as well as the power steering lines, again to keep it clean.

I chose to do the fuel system in braided stainless only because I'm guaranteed no leaks and no corrosion. The most invasive part was running the return line to the filler tube for the gas tank. Best way to do it for me was just cut a gap in the floor, drop it in, and then glass in a new floor over it... not as bad as you would think!

I'll try and get some pics together, and post them. In the meantime, if you want more info, or have more question, I'll be more than happy to help. I had to figure this out on my own, so I know how discouraging it is when there is little info out there on the topic.

And then there are the guy's that say you're wasting your time.. a carb works fine when it's set up right. Well the reallity of it is, a carb usues a float to maintain a fuel level, have you ever seen a boat that is always at the same level????? Or even level for that matter???? Fuel injection, when set up properly, is far more reliable, better with gas mileage, and response is night and day!

What I'm learning as I tackle these seemingly overwhelming projects, is that nothing is impossible, and it's usually not as bad as you would think.

 

[Ole Sarge]

Re: Engine Swap, EFI or Not??

Very nice indeed. If it is an MPI, it would seem feasable to just use a late
80's Camaro MPFI setup? The harness and ECM are pretty much completely seperate entities from the rest of the electrical system, should be not too bad a swap. That's what I did with the Scout. Trimmed the excess off the harnes, terminated a few un-needed pins on the ECM, provided switched and constant power and grounds for ECM and sensors. Wah-lah, working TBI! Should be the same for MPFI, only real difference is manifold, higher press. fuel pump, and maybe ECM wiring diagram. I'd like to make my own, kits are nice, but home made is AWESOME!

Didn't think about not needing an O2 sensor, I thought that once the engine warmed up it was pretty critical.

Thanks

 

[dlktdr]

Re: Engine Swap, EFI or Not??

Honest Don, thanks for the reply that setup sounds awsome. I have decided to go with a rebuilt 351 block and just keep the carb for now due to $$$ issues.. I was thinking about making some minor upgrades to get around 300hp total. EFI will have to be later..