1988 3.0 and 1994 3.0 swap

[markhodges78]

I have a 1994 seapro with a mercruiser 3.0 engine it's starting to show signs of oil blow by pretty bad. I checked the compression and all cylinders were around 130psi.
The engine runs pretty good for the most part the with the only issue being that when I come off plane it ideals around 900-1000 rpm.
If I blip the throttle it will settle down to 650. also I have verified that's it's not in the cable! When this happens I go back and force the arm back with out any change in rpm because it's already setting against the idle cam. It's almost as if the engine has un burnt fuel that is burning off.
So the reason for this post is this I have a 1988 3.0 that I just removed.
Its from a boat with a rotted floor that has between 169 to 178 psi of compression across the cylinders. So my question number 1 is can this engine be made to work with my distributor and coil while maintaining the same specs as the 1994 engine..

Question number 2 I also have a boat with a mercruiser 4.3 engine in it. Would the extra performance ( speed ) gained from the 4.3 be worth the increased fuel usage. Right now I get about 32 mph with just me on the boat with around 11 mpg of fuel usage.

Thanks Mark

 

[alldodge]

Not sure but think the 1988 might be a 2.5 maybe @Bondo might know for sure

As for the 4.3 it will burn a slight bit more fuel because it weights more then the 3.0

So long as you stay away from WOT it should be fine

 

[Scott Danforth]

the 4.3 will actually use less fuel overall than the 3.0

remember, with 3.0's you want to stick with 1990 and older or 1991 and newer to not mix generations

 

[Bondo]

Not sure but think the 1988 might be a 2.5 maybe @Bondo might know for sure

As for the 4.3 it will burn a slight bit more fuel because it weights more then the 3.0

So long as you stay away from WOT it should be fine

Ayuh,..... A 2.5l has just a pulley on the crankshaft,......

A 3.0l has a pulley, 'n harmonic balancer,.....

 

[markhodges78]

Not sure but think the 1988 might be a 2.5 maybe @Bondo might know for sure

As for the 4.3 it will burn a slight bit more fuel because it weights more then the 3.0

So long as you stay away from WOT it should be fine

it says 3.0 on the valve cover so I assumed it is

Yeah I realize the 4.3 may burn more fuel but do you think it will be worth the performance gain.

Thanks Mark

 

[markhodges78]

the 4.3 will actually use less fuel overall than the 3.0

remember, with 3.0's you want to stick with 1990 and older or 1991 and newer to not mix generations

As in not mix the parts off the blocks or not mix the engine with the stern drive ?

 

[markhodges78]

Ayuh,..... A 2.5l has just a pulley on the crankshaft,......

A 3.0l has a pulley, 'n harmonic balancer,.....

I will check this as well

 

[Scott Danforth]

As in not mix the parts off the blocks or not mix the engine with the stern drive ?

Both

 

[markhodges78]

Both

Sorry if it's a stupid question but is a 3.0 engine not a 3.0 engine. Engine swapping is completely new to me

 

[alldodge]

If i

it says 3.0 on the valve cover so I assumed it is

Yeah I realize the 4.3 may burn more fuel but do you think it will be worth the performance gain.

Thanks Mark

I would do it just knowing g what you have said

 

[Scott06]

if there is room under the engine hatch / compartment i would swap in the 4.3 definitely worth the work. Issue will be if you have a doghouse style engine compartment it may not be wide enough, and the 3.0 uses a front engine mount vs the side mounts on a 4.3. If the stringers arent thee for side mounts they need to be fabbed up, nit sure if this is within your capabilities. If you go this route you will need to step up about 2” in prop pitch. Nit sure if wye pipe will fit your later gen 2 transom housing

you can swap your complete 1988 over as long as you keep the flywheel and coupler for the 88 with it. In 1990 the 3.0 went to a single piece rear main seal and triangular flywheel mounted coupler vs crank mounted coupler on earlier ones. If you have these complete should swap over.

 

[markhodges78]

Thanks guys you have all given me plenty ideas to check, confirm, and decide on truly appropriate it

 

[Scott Danforth]

Sorry if it's a stupid question but is a 3.0 engine not a 3.0 engine. Engine swapping is completely new to me

in 1990 the motor went thru a major re-design for 1991. the crank went from a 2-piece to a 2-piece. at the same time, the block changed, the head changed, the pistons and rods changed. the use in boats went from the 153 tooth flywheel to the 168 tooth flywheel

yes, while they are both 3.0. best not to try to mix generations

so for your 1994 boat. stick with a 1991 or later 3.0

or swap to the 4.3 which will require a complete motor/drive swap

 

[Bondo]

in 1990 the motor went thru a major re-design for 1991. the crank went from a 2-piece to a 2-piece. at the same time, the block changed, the head changed, the pistons and rods changed. the use in boats went from the 153 tooth flywheel to the 168 tooth flywheel

yes, while they are both 3.0. best not to try to mix generations

so for your 1994 boat. stick with a 1991 or later 3.0

or swap to the 4.3 which will require a complete motor/drive swap

Ayuh,..... That should say, from a 2 piece rear main oil seal, to a 1 piece rear main oil seal,....
Which required a crankshaft change, 'n a block change to match,....

 

[markhodges78]

Ok so I pulled the 3.0 engine out of the donor boat today the serial number is C338853 The crank does have a harmonic balancer on it and the coupling bolts to the flywheel with 3 bolts

 

[Scott06]

Ok so I pulled the 3.0 engine out of the donor boat today the serial number is C338853 The crank does have a harmonic balancer on it and the coupling bolts to the flywheel with 3 bolts
View attachment 371361
View attachment 371362
View attachment 371363
View attachment 371364

That serial shows both style couplers were used early and late so maybe doesnt denote two or one pice rms… parts 25&28

Crankshaft, Camshaft, Water Pump (140-3.0l / 181 Cid) for Mercruiser (120 HP / 2.5l140 HP / 3.0l R / Mr / Alpha) Engine

www.marineengine.com

either way if yiu keep the complete engine together should fit basically drop in…

 

[alldodge]

The balancer shows its a 140hp 3.0

 

[markhodges78]

Well it's official I'm going to be converting to the 4.3. The engine bay area is actually a few inchs bigger in my boat then it is in the boat that the 4.3 is in now.
I believe that the 4.3 was an option for my boat as well but it doesn't have the engine mount beds for one .
Should I continue with this thread with question about building the beds or create a new thread ?
Thanks Mark

 

[alldodge]

I'd start another