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3.7 conversion to ?

R

Reddman

Member
Hi all,

I have a 21' glass boat with the 4 cyl. 3.7 liter motor. Last time I hit out it would not get on plane. Upon inspection I found water in #4 cylinder. I was told this is pretty normal for this motor. So I would like to upgrade maybe to a V6 or ? Any hints on what motor would make for a good replacement & still be economical?

Thanks for hearing me out & any advise.

Reddman
 
There are several things that need to be considered.

What are you looking to accomplish? More power, A lot more power, fishing, pleasure boating, pulling skiers or tubes or knee boarders?

How much space do you have between the transom motor mount now?

Depending on the space this could determine what motor you use. A V8 needs more forward space to fit the a V6. What that is exactly I am not sure as most boats are shrink wrapped for the winter so I cant measure one now.

Also a 3,7 and the smaller 3,0 4 cylinder motors uses a front motor mount and NO side motor mounts like the V8 and V6 use. The v8 and V6 do NOT use a front motor mount.

What this means is you may need to come up with some king of mounting platform (stringers).

Your boat now has a transverse (side to side) stringer where the front motor mount, mounts.

V8 and V6 motors have stringers that are from the transom and go forward typically all the way to the bow. Yours may have these after the cross/transverse stringer there now but they don't go back to the transom.

So you would need to make some and fiberglass then in place. If you choose that path then height, width and the gap or distance between them would need to be acquired. Most any boat with a v6 or V8 could be used for gap measurement but the height depends on your hull design.

So if we come up with the space you have from the transom to front motor mount and any additional space before the floor that would be a start.

Then more dimensions on the hull/bilge and getting the stringer width and thickness needed.

A V6 with a 4 bbl carb will be ~ 200 hp
A V8 305 with a 2 bbl carb will be ~ the same but more torque .
A V8 350 4 bbl will be ~260-270 hp and even more torque.

Then comes the outdrive ratio...

Your current outdrive ration is most likely 1.84:1

A typical V6 is looks to be the same 1.84:1

A V8 typically is 1.50:1
 
kghost,

Thanks for the info, We use the boat for fishing in the Columbia river, crabbing & pleasure boating in he San Juan Islands. Looking for a little more power. Hull has both stringers, front to back & side to side. It is a full walk around with a small cuddy. I am leaning toward the V6 since the outdrive is new & is 1.84:1. I will get the measurement from the transom to the front mount & get back with the info.

Thanks

Reddman
 
If that is the case then you may get out of this easy.

What I would suggest is to search for repowered boat that had a V6 and went bigger and maybe you could get a complete motor then all you would need is a few extra parts.

Craigslist has them and I have seen a few over the past year. Or check with marina's in your area.

I am not 100% sure if the transom mount will be the same but maybe some others here can add that info.

Gen I which your is (outdrive) went to 1990
After 1990 it became Gen II

Not sure if there is any difference in the transom mount....

One thing for sure is, get rid of the factory fuel pump set up and replace it with a stand alone marine electric fuel pump such as Holley or other major brands.........They are much more dependable.
 
Ayuh,..... While not completely painless, the 4.3l swap is the best bet goin', to replace a 470,....

If nothin' else, because the drive ratio will work Ok with it,....
 
Thanks for the input guy's.
This boat is a 1990 Freedom 21' walk around, gen 1 outdrive. Do I need to find a pre 1990 motor for this or will a newer motor work as well?
 
Have you, or would you consider finding a donor boat with a Volvo Penta system, such as the AQ205 (GM SBC 4.3L V-6), and the AQ series stern drive as a replacement?
This would give you nice smooth Cone Clutch gear engagement, in lieu of Merc's Dog Clutch gear engagement.
With the AQ series........ there is no concern for annual engine coupler alignment, no rubber hub drive coupler issues, no Gimbal Bearing, no SI or SA do deal with, etc.

I have done several of these or similar type conversions. All have been very pleased.

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Volvo-Penta-AQ205A-SP-Abbildung.jpg



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fastjeff said:
I hope that V-P unit has power trim. Mine didn't and it got a bit chilling messing with tilt pins!

Jeff
Click to expand...

Jeff, I certainly understand that.
I specifically listed an AQ series drive that did offer PT.

Many of us forget, or just don't know, that beginning with the 290, all VP drives following are Power Trim drives.
When we reach the "C" and later, they are excellent drives.

The AQ series gasoline engine line ran into and through 1996, and in the Diesel engine line, into 2000, all right along side of the SX and DP-S style Gimbal System drives..... AQ series being the better main suspension fork/pivot tube geometry.



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"""""""""This would give you nice smooth Cone Clutch gear engagement, in lieu of Merc's Dog Clutch gear engagement.
With the AQ series........ there is no concern for annual engine coupler alignment, no rubber hub drive coupler issues, no Gimbal Bearing, no SI or SA do deal with, etc."""""""""""""



The Mercruiser outdrive clutch dog design has been in use for over 50 years.........No issues what so ever and shifting into neutral does not require the drive to be spinning.

The alignment is ONE AND DONE! I have never touched mine and I have owned my boat for 21 years.

My boat is a 1987 with the original coupler...............and only a second gimbal bearing over 29 years (non sealed and needs to be greased annually) new gimbal bearings are sealed and are non serviceable so they last much longer.

The (SI)(Ugggg) or shift interrupter works perfectly well. Again mine is 29 years old and still functions perfectly. I have never had to do anything to it.

Why waist money on a brand that is expensive to repair, Hard to get parts for, even harder to find a qualified service center?

Mercury is like Chevrolet........they are everywhere and so are the parts and service centers............and people who know how to fix them..........
Unlike Volvo Penta..........Just like there auto's............
 
Hi guy's,

Here's my 2 cents on this. Last summer I hit something with the lower unit. I was not comfortable with just replacing just the lower unit so I had the complete outdrive replace with a brand new one. $3600.00 There for I will go with the Mercruiser & stay married.

Reddman
 
Reddman said:
Here's my 2 cents on this. Last summer I hit something with the lower unit. I was not comfortable with just replacing just the lower unit so I had the complete outdrive replace with a brand new one. $3600.00 There for I will go with the Mercruiser & stay married.

Reddman
Click to expand...

With that now known, I too would stay with the Merc.


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Jack,

I seen that yesterday, nice unit & good price. But I am going to hold off until I get the damage repaired from the storms we had this winter.

Reddman
 
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