Swappable Engines & Drives

[myoldboat2]

Is anyone else interested in a thread for the Adults Only section that would list what engines can be swapped and what sterndrives (or drive shaft housings and gear housings) can be swapped? It seems to be a fairly common question.

For example, I'm not currently looking to replace anything, but there will probably come a time when I need to replace my engine or drive or both. I have a 1974 Mercruiser 140 with Late Model I sterndrive. I'm curious if there is a way to go to more power without having to totally rebuild the transom and engine room. (I realize transom strength is a different issue; I'm just talking about dimensions, mounts, engine/drive compatibility and so on.) Thanks.

 

[cr2k]

Re: Swappable Engines & Drives

Not mention changing the upper drive or at least the gear ratio.

 

[Bondo]

Re: Swappable Engines & Drives

I'm curious if there is a way to go to more power without having to totally rebuild the transom and engine room.

Ayuh,.... Generally speaking,.... No....

 

[erikgreen]

Re: Swappable Engines & Drives

I'm curious if there is a way to go to more power without having to totally rebuild the transom and engine room.

Sure, there absolutely is!

They're called outboards.

 

[jtybt]

Re: Swappable Engines & Drives

Welllll, I can tell you that the merc cut-out hasn't changed between at least 1978( my boat) and early 1990's Bravo( what I swapped) so chances are the cut out has been pretty standard.

I know the early merc had different length upper drive shafts and different spline patterns but I forgot what was what.

OMC has had a few changes, as Don has posted.. I guess Volvo and OMC came together with the same drive and cut-out around '95.

Someone has got to know more than that.

 

[dubs283]

Re: Swappable Engines & Drives

I guess Volvo and OMC came together with the same drive and cut-out around '95.

Volvo bought OMC's sterndrive division in 1994 and part of the deal was Volvo was allowed to use the OMC Cobra name for a few years, these drives ARE Volvo drives, NOT OMC Cobras

 

[erikgreen]

Re: Swappable Engines & Drives

Joking aside, I think it would be helpful to list authoritatively (with research backing it up) which Marine engines are variants of which car engines, and which years of marine engines of the same type can swap.

Unfortunately you'll find that the options for swapping to a different engine type (upgrades) are very limited. This is due partly to the way Mercruiser and Volvo designed their drive systems, and partly to the need to design a boat for the weight of the engine you'll use. Some boats can use several different engines, but I think they usually try to balance the weight out by moving a few other items.

What you'll mostly find is the engine equivalents in Marine and Auto, IE stuff like 1982 GM V8 is sort of equal to MCM260. You won't find a list of motors you can swap in for a GM inline 6 easily with significantly more power, nor major tweaks you can make like hot rod cars that'll add enough power to be worth it.

Repowering is something you do if you have to or really like the boat, not something you do for more power. It's too much work and cost for anything but an expensive boat or one you love.

If you want more power, buy a bigger boat with a bigger engine.

You CAN rig your boat up with a non coast guard approved hot rod engine provided you are good with engines and have a machine shop... unless you understand boat engine performance though, you'll probably be disappointed with the results. You need different performance in a boat than a car, and the folks here who deal with standard parts won't be able to help much if something goes wrong.

Anyway, just my rambling thoughts. Carry on.