3.7 to 4.3 swap?

[Rick Stephens]

Don't encourage him.


Everyone else should have cake and ice cream. But Mike needs more HP like a cat needs another hairball to puke on your bed. He loves his Mercruiser abomination. And rightly so. Think of the spare parts collection he would be foregoing.

 

[stonyloam]

Yeah and I can use a lot of those parts

 

[nola mike]

Don't worry Terry, it will probably be a few years at least. Haven't seen Eric around lately, you'd be the last 470 man standing. Had 11 in the boat today, I didn't like how it handled. I'd worry about an extra 400# back there. Plus fuel economy. 4.3 might be worth it if I could get 210+ hp without doing anything crazy. Would love efi, but might be tough to find a junker hull. No Rick, why did you go with the 4.3 v. 5.7?

 

[stonyloam]

11!??? That 5.7 would have sunk it

 

[Rick Stephens]

No Rick, why did you go with the 4.3 v. 5.7?

Mike, a couple reasons. First was, I had a complete 4.3L Vortec, Alpha1 Gen2, power package sitting there on a fallen apart deal. Second, my (little) 17 foot boat came with 2 engine package options, the 3.0L or the upgrade to the 4.3L. So I knew it could handle the 4.3. It was a close fit, but a 5.7 would have fit pretty much the same. I just can't imagine needing more than the 230 or so HP this motor is putting out, this boat screams. Mainly, like you, I didn't 'need' more power. I mostly fish and pull the kids around on wakeboards, and a 3.0L will get you to the fishing grounds as good as a 454, only a lot cheaper. But, midlife crisis intruded and that 4.3 called to me, over and over.

The one place I really could use more power is I like to ski and my 25 year old 3.0L was pretty pathetic getting me up. I turn 60 this winter, and just had knee surgery to clean up a problem caused throwing hundreds of batting practice pitches a day while coaching HS baseball. I don't figure I would ever get back up on the ol' 3.0. I don't think I'll have a problem with the 4.3, haven't tried yet though.

You might question my 230 HP claim. That is just what I figure my motor is putting out. The block is pre-Vortec and pre-balance shaft. The top end is Vortec, roller cam, Performa intake and Edelbrock 1409 carb. That is according to Merc a 230 HP (at the flywheel) motor WITH the balance shaft. Without a balance shaft I should be a bit higher as turning the balance shaft costs around 15HP. I virtually never open up the secondaries on the carb. The boat smokes along compared to the 3.0L days. More motor than an old goat like me really needs. I do look forward to coming across the young guy who sold it to me though. I figure to offer to race him for a C note - tell him I got a new prop. He bought a dedicated ski boat that would have handily beat the 3.0L

 

[nola mike]

210+ hp would probably make the swap worth it. And no hurry, so I can take my time looking for a deal. I think a 4.3 would be the way to go--my hull is just too light for a v8. I'd also be able to keep my gen 1 outdrive (maybe?). It looks like the balance shaft started appearing in '93 in cars, when in boats? Is it as simple as finding a non-balance short block and throwing vortec heads on it? And I'm sure I know the answer to this, but is it possible to use the FI from a truck motor? Otherwise, can I use a stock 4bbl carb/intake/cam to get to 210hp?

 

[nola mike]

Also, my buddy just blew the coupler on his formula with a 4.3, was going to fix and sell--I might look into it. I know it has a 4 bbl carb, but don't know the rest of the particulars...

 

[Rick Stephens]

Doesn't matter whether you go with or without a balance shaft. Vortec though, absolutely. Nice part with pre balance shaft is the steel timing cover instead of that near useless plastic one. The reason GM went with a balance shaft is the V6 is so unbalanced. But smoother running has its own advantages. Some folks have complained over vibration with non-balance shaft V6. Mine seems to run smooth enough.

I think your main criteria is going to be Vortec, which adds a solid 20HP. Which means '96ish or later or a trip to the salvage yard for a set of heads and an intake.

 

[nola mike]

I've read (and you yourself said Rick Stephens ) that the balance shaft robs 15 hp. Looking up the HP ratings on these things, talk about confusing. The highest rating that I could find for carbed models was 205, though I'm not sure if that's a prop or crankshaft rating (looks like merc went back and forth on these). If that's a prop rating, that would probably be close to the 230 crank that you're talking about. My 170 would probably be only rated 155 or so at the prop, so that would be a huge difference. Guessing that I'd also need a 1.5 outdrive for that though. I currently have a 1.84 with a 23p prop...

 

[Bondo]

Guessing that I'd also need a 1.5 outdrive for that though. I currently have a 1.84 with a 23p prop...

Nah,.... That's 1.65:1 territory,....

 

[Rick Stephens]

I'm running the 1.84 outdrive that came stock on the donor boat with the 4.3L. I thought the 1.65 was for the 5.0L.

 

[nola mike]

Forgot about the 1.65. Either way, I'd need a new outdrive. If I can reprop my 1.84, than the swap isn't worth it What prop are you running Rick Stephens ?
Gotta figure out what years to look for on a donor, and whether the balance shaft is something I should try to avoid. Tell me if I have this right:
Bottom ends: Performance wise, pretty much the same with the exception of balance shaft. 1 v. 2 piece rear main seal at some point, is that a big deal? At some point they went to a serp belt, which adds a few hp?
Pre-93 or so, no balance shaft. Still not sure how important this is
Top ends: Would want the vortecs--post '96? Guessing these are easy 'n cheap to find at the wrecker
Fuel: 4bbl carb is probably the most realistic option (v. EFI). Did they all use the same Rochester q-jet? The thought of working on one of these is not appealing. I know I can go aftermarket, but I'd have no idea how to tune it. Guess I can learn.
Intakes: Are there just different intakes for the 2 or 4 bbl versions?
Ignition: TB IV or V, assuming this isn't a big deal.

Breaking news: Just saw that my boat was offered with a "OMC 175", which appears to be a 4.3. Guessing '86 would be a cobra, so there's a good chance that I already have my mounts where I need 'em, right?

 

[Rick Stephens]

I went to a 21 pitch 4 blade Solas Rubex on the 4.3L with the 1.84 ratio drive. It was on sale at iBoats at the time and came with hub, nut and washers kit. That was my shot in the dark since I didn't have a decent test prop. Worked out well since it tops out at about 47 MPH and 4800. I think I could get 50 MPH if I got a better prop for speed. Bit I don't really care all that much and the 4 blade 21 jumps out of the water like a tractor pull.

I doubt you have mounts. However, the lid is likely to fit since the manufacturer would want the same one for all motor options.

I think you'll have to weigh what you find a good deal on as far as ignition, balance shaft and carb. There were Roc QJets and Weber 4 barrels used by Mercruiser. I had a QJet on my donor motor, but it needed a 1 inch adapter to fit the Edelbrock Performa square bore intake manifold. That made me an inch too high for the doghouse. So I bought an Edelbrock 1409, which is a square bore and rid me of the adapter plate, and calibrated it. There a few of us on the forum who have done the calibration pf the 1409 on a 4.3 Vortec and can save you a lot time and effort. It isn't hard, I did changes of jets, needles and rods sitting in the water a number of times. And checked spark plugs for different operating ranges right on the lake to get it perfect. The Weber is identical to the Edelbrock 1409, so all the Mercruiser parts like stainless fuel line from the pump, fit either. I MUCH prefer working on the Weber/Edelbrock over the QJet.

Ignition is what it is. If the day comes you have to replace the module on a Thunderbolt IV/V do what I did and just get a Delco Voyager EST. Cheaper than the module for the whole setup.

I don't think I would care whether a motor had the balance shaft or not. I suppose you could always leave it out. The harmonic balancer is different though, they consider that an internally balanced motor and the balancer is doing a lot less. So scratch that idea. Either way, nothing wrong with a balance shaft - all 4.3's ended up with them as of '92 on the GM line, prolly '93 at Mercruiser. The balance shaft block does not have a provision for a mechanical fuel pump. So you have to go electric. Some pre-balance shaft blocks do not have the mechanical pump opening, mine is one. At first that bugged me, seemed one more thing to go wrong. But electric pumps are in everything these days and are pretty good. I used the OEM Airtex pump without paying Merc prices.

Takes a lot of time to study up the parts you'll need. A donor boat is likely to come with an outdrive, maybe an appropriate prop to start out with. I enjoyed the hell out of the project and ended up not spending much since I sold off EVERYTHING I pulled.

Rick

 

[Bondo]

Breaking news: Just saw that my boat was offered with a "OMC 175", which appears to be a 4.3. Guessing '86 would be a cobra, so there's a good chance that I already have my mounts where I need 'em, right?

Ayuh,.... You Don't want anything OMC,......

Go for a post-96, with a 4bbl carb,.....

Mine is a '94/ '95 with the balance shaft, 'n 4bbl,.... been a Great motor for the last couple thousand hours of run time so far,....
Got Vortec heads for it, but don't wanta waste time on this ole barge, got others in progress,...

 

[nola mike]

No, Bondo, the point about the omc was that if a 4.3l was an option from the factory and was a cobra, the boat might not need any mods for a merc 4.3...

 

[Bondo]

Gotcha,....

 

[nola mike]

Peoples' heads would explode if I went from a 470 to an OMC

 

[stonyloam]

Going to have to learn how to winterize that new engine, no more 5 min. and done. Would hate to see a nola mike cracked block thread some spring

 

[nola mike]

Won't be this spring. I'm still working on the interior, and have a few "real" projects to do before I tackle a "fun" project (per my wife). Looking for some reman 4.3s (ouch). Interestingly, michigan motorz has their 4bbl vortec listed as 225 crank hp, which would be sweet. Still wishful thinking currently. I'm curious as to how tired my engine actually is. Compression has always been good, but It seems like it's lost a step. May throw a vacuum gauge on for fun. Going to see if my stringers need new mounts or not today. Seriously though stonyloam , if you had to replace your engine, and could drop in a v6 with 50% hp, you wouldn't do it?

 

[Scott Danforth]

Peoples' heads would explode if I went from a 470 to an OMC

No, we would just have you committed