3.7 L 170 188 190 224ci mercruiser

JT78

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Jan 9, 2021
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13
Let’s start a discussion what you hate what you like about this engine.along with other fixes I have made a few modifications to mine
I’m trying to revamp this bad boy and turn it into what it should have been . Any discussion on this beast is welcome
 

Scott Danforth

Grumpy old guy who plays with boats
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Jul 23, 2011
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34,063
lets not. its been rehashed to death. however for some reason the search function isn't pulling up the past lists.

assuming you have all the updates done over the years...... larger heat exchanger, exhaust elbow change, etc.

so much easier and cheaper to pull the motor and drop in a proper motor that has support. unless you have twins closer together than 34" then you are stuck with the platypus motors

issue #1, aluminum block and iron head. only an engineer that went out for lunch and smoked peyote then listened to the accountants would do this. dumb as dumb could be. solution - edelbrock aluminum head (ford FE motor - 460)

issue #2, the open deck or floating bores. cylinder bores need to be stabilized. usually results in some minor machining and a 7 gauge laser cut "spider" is welded in the top of the deck to keep the bores from moving around

issue #3 the charging system. both the anemic charge coil in the front damper and the required water cooled regulator. these are outboard parts. Mercury Marine used these because they were cheep. 'nuff said

issue #4, 5, 6, 7 - using a rubber raw water impeller as the cooling water circulating pump. rubber not intended to run that hot. using a custom made cam without heat treating the cam drive stud was simply stupid. relying on cheap seals to keep oil and coolant from mixing. most peiole putting a scew in the weep hole because they thought they "fixed it" seriously, there should have been a real waterpump

issue #8 - motor is half the pistons and rods from a Ford 460 with a GM patterned flywheel and a GM like timing setup all while connected to a custom mercruiser crankshaft. this means you are stuck with the stock grinds for the cams for a boat

now, these motors have been used in various hotrods and these are the fixes for the shortcomings in a car (most can be used in a boat).
aluminum head with some modification is easy (boat friendly)
the open deck fix is a bit more difficult unless you have access to a 5000 watt laser or larger and a machine shop.(boat friendly fix)
with a bit of work, a new front damper can be had. and if you want, an alternator can be fitted. (alternator conversions are common in boats. no need for the damper change unless your racing)
a bit of welding, an electric water pump from either Mezzier or davis craig can be used for a circulating pump. especially when re-routing the cooling lines, etc. (this is a hot-rod only mod)
there are a few hot-rod cam grinders that can make a decent cam. (again, not needed in a boat)
normally these motors end up with a custom header and custom intake.

by the time you take the motor out, and fix all the items that need fixing, a 4.3 would have been installed and you could have been back on the water for much much much less time and water. unless your boat has twins closer together than 34"
 

nola mike

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Apr 22, 2009
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2,679
Having just done this, I disagree. All the shortcomings listed are there. I ran the crap out of mine for 12 years without the cam issue. Never blew a hg. Never overheated. Did the alternator fix, which was like $300 and 2 hours. A non issue. The 4.3 is significantly heavier, which makes a big difference in a small boat. The 4.3 is for sure the better engine, but for most people I think you're better off keeping the 170.
 

JT78

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Jan 9, 2021
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I love both your responses Scott I love you’re a grumpy old guy who plays with boats the grumpy part especially cause I’m a grumpy middle aged dude lol. I’m also a machinist by trade and have to do 70% of our factory maintenance, we also do heat treat case hardening through hardening air/oil quench nitride induction flame hardening ect. The pay sucks so looking for an out. But I restored my boat 76 cobia for some crazy reason went all in new stringers bulkheads transom deck and literally went overboard with it, big mistake I know but it’s been fun. Realizing my boat only has capacity for 900 and some lbs motor out drive and fuel I knew I couldn’t go from a 120 merc to a 835 to 865lb or whatever 4.3 to 5.7 I have had and currently run all sbc v6 v8 in my daily driver’s and I love them so weight for the boat became my issue. I started research and discovered this as I call it a diamond in the rough 3.7l . I’ve built 350’s 305’s Ford baby 6 inline. My daily driver is a 2000 blazer 4.3 that I built the motor in. My first car I built was a 81 Camaro with a 3.8 229 pred to the 4.3 I’m a Chevy guy all the way. But I ended up buying a boat for parts with an ‘86 190 so on a wim tore the motor down realized mercruiser failed a few spots but for the most I see it’s an ingenious design that’s shadows by a few flaws. I’d love to be able to find out how many are out there running today. I can go on forever about this motor. In 1989 this motor was producing 190hp @ 275ftlbs of torque 4.3 190hp at what 250 265ftlbs matches our forklift at work. But the 3.7l sipped gas better than the 4.3, and was lighter.

thank you for your responses again loved both
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
34,063
I would not jump from a 2.5 to a 3.7

i would jump from the 2.5 to a 3.0 (direct bolt-in and only about #8 heavier)
I would jump from a 2.5 to a 4.3

the 2.5/3.0 and the 4.3 weight the same, and the 4.3 is shorter

the only reason the 3.7 could burn less than a 4.3 is how its commanded. both motors have a BSFC of 0.4#/HP/hr
 

nola mike

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Apr 22, 2009
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2,679
I would not jump from a 2.5 to a 3.7

i would jump from the 2.5 to a 3.0 (direct bolt-in and only about #8 heavier)
I would jump from a 2.5 to a 4.3

the 2.5/3.0 and the 4.3 weight the same, and the 4.3 is shorter

the only reason the 3.7 could burn less than a 4.3 is how its commanded. both motors have a BSFC of 0.4#/HP/hr
Agreed. I certainly wouldn't go out of my way to install one, though if I had a good engine already I'd consider it. The 3.7 only made 190hp with the 4bbl carb, which is pretty rare. Either way you're making new mounts. My 4.3 actually burns less fuel then the 3.7. I'm thinking that the 4bbl is more efficient with only the primaries open. That said, I'm still one of the only, if not only, supporter of the 3.7 around here. As far as power goes, the juries still out for me. So far I'm a bit disappointed with the 4.3. Top speed is maybe 1-2 mph better, but I'm still working on carb tuning. I haven't skiied behind it yet, which was a big motivation for the swap. I think I underestimated the effect of an extra 2-250# in a 1500# boat. As far as the overall engine, the 4.3 is much smoother. Though the results are similar at wot, the 4.3 doesn't feel like it's working hard at all to get to 40+ mph.
 

JT78

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Jan 9, 2021
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Mine is an 86 190 4bbl doing research I’ve read it’s 6 inches longer than a 3.0 but I measured everything between the 2 it’s only a little over 3 inches difference, l guess did good when I rebuilt all stringers motor mount for the front ect. I gave myself the option for all but inline 6 lol. But my boat is rated for 975lbs engine out drive and fuel a 4.3 is 865lbs with out drive full tank that’s 20 gallons is about 160 lbs that’s over my max 3.7l is anywhere from 150 to 200lbs difference which makes sense all aluminum but head crank rods and cam. This motor is pushing out 275 ft lbs of torque. I have read the pertronix conversion helps with vibration also if you go with pre balance shaft 4.3 you’re going to deal with a rough running engine. I pulled the engine down to check everything before I ordered the first item for it. Have no clue why this motor was taken out of service spun free no sign of blown hg but the end of the cam was grooved. Someone was putting either bad municipal water or well water in it cause the water passages were filled with calcium. I think the speedy sleeve is not the best fix for the cam cause you would have to remove it to get timing gear off. I will attach photos of before and after of my fix. Cast iron with rubber seals are a no no rubber hardens and will act as a turning tool against soft material.
 

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JT78

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Jan 9, 2021
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Having just done this, I disagree. All the shortcomings listed are there. I ran the crap out of mine for 12 years without the cam issue. Never blew a hg. Never overheated. Did the alternator fix, which was like $300 and 2 hours. A non issue. The 4.3 is significantly heavier, which makes a big difference in a small boat. The 4.3 is for sure the better engine, but for most people I think you're better off keeping the 170.
Do you still run yours
 

JT78

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Jan 9, 2021
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You might have to down jet it may be too much fuel I’m pretty sure even the quadrajet has smaller jets for the smaller displacement motors. Also I bought a new 600 edelbrock about 10 years ago I think it was the 1404 I had so much trouble getting it tuned in finally I pulled it off and went through it and found a bronze chip in one of the primary venturis I had to get it out the hole with tweezers put it back together new air horn gasket and it ran beautiful guess it got passed quality control.
 

Scott Danforth

Grumpy old guy who plays with boats
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Jul 23, 2011
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34,063
No way the pertronix ignition can fix the imbalance caused by a big 4 banger without adequate crank damping

You may want to actually weigh a 4.3 longtail and compare to the 2.5 you pulled out.
 

JT78

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Jan 9, 2021
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No way the pertronix ignition can fix the imbalance caused by a big 4 banger without adequate crank damping

You may want to actually weigh a 4.3 longtail and compare to the 2.5 you pulled out.
I’m not sure how just read a post recently I found that was an older post where a fellow claimed that but hey he could have had a bad misfire before he did the conversion.
 

Scott Danforth

Grumpy old guy who plays with boats
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Jul 23, 2011
Messages
34,063
a misfire is a sign of poor maintenance.

you cant smooth out the 3.7 with an ignition change
 
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