4.3omc i/o and motor conversion to mercruiser

[Lou C]

Re: 4.3omc i/o and motor conversion to mercruiser

"The conversion (including labor), should cost no more than about $2500-3000. The kit is about $350 retail and the drive will be modified for free if you buy it from SEI or one of their dealers. Expect about 6 to 8 hours of labor by a tech has done the install before. I can do one with my tech in less than 3 hours."


Just wondering what modifications need to be done to the drive...can a standard Merc drive also be used with this conversion...or does it have to be modified by SEI for it all to work?
It sure is more financially practical than the SX conversion...those drives retail for big bux unless you can find a good used one...like they are double the cost of an Alpha new...and 3 times the price of an SEI...

I can still get good service on my Cobra and my mechanic can rebuild them in his shop...he went to the OMC school and has all the special tools...so for now I am OK with how it is but if he retires one day and I want to keep this boat...its either that or a complete repower with Merc stuff...

 

[Ducatinut]

Re: 4.3omc i/o and motor conversion to mercruiser

"Just wondering what modifications need to be done to the drive...can a standard Merc drive also be used with this conversion...or does it have to be modified by SEI for it all to work?

Lou--

Any "Gen 2" drive can be modified. The modification is simple, not even requiring that the drive be disassembled. However, the measurements are pretty critical and any variation can potentially cause issues. Having SEI do the modification preserves your warranty and ensures that the dimensions are correct.

Besides, once it's officially released to the public, a DIY'er can purchase every part needed for around $2K(including the drive) and you get a warranty that can't be beat (if you ever actually need it).

It sure is more financially practical than the SX conversion...those drives retail for big bux unless you can find a good used one...like they are double the cost of an Alpha new...and 3 times the price of an SEI...

Volvo & Merc are REALLY proud of their drives (I think that your prices are conservative). Plus, that Volvo dealer is going to nail you to the wall for the other little parts that you need (gimbal housing - $400+, raw water pump - $150+, new prop - $150+).

That observation was a prime mover in this project. It also produces a side bonus, the kit should work fine in an SX-derivative rig with the addition of a shift interrupt system (next on the list). Keep in mind that the SX is effectively a Cobra with VP guts.

I can still get good service on my Cobra and my mechanic can rebuild them in his shop...he went to the OMC school and has all the special tools...so for now I am OK with how it is but if he retires one day and I want to keep this boat...its either that or a complete repower with Merc stuff...

If you can get service for your drive, an investment like this doesn't make a lot of sense, until you need a new lower unit or whatever. The Cobra is a great drive (better than the Alpha, IMO)

There's still a lot of very nice Cobra-powered boats out there and this gives their owners a choice when it comes time for a new drive.

Fair winds,

Chris

 

[rodbolt]

Re: 4.3omc i/o and motor conversion to mercruiser

last cobra to SX conversion kit I priced was almost 8000 dollars by the time it was gonna be installed.
we fixed the original cobra unit .
shop I currently work at has no tooling for cobra units the shop I worked at in portsmouth VA still has all of it so thats where I send them.
that is a neat looking conversion and the SEI products I have sold and installed always worked as advertised and ya simply cannot beat that warrenty.
infact I wont rebuild alpha drives anymore due to the low cost and warrenty of the SEI.
the SX doesnt need a shift interupt switch and will outlast the alpha 5 to 1 easy.
however the SX is about 5K new.

 

[Lou C]

Re: 4.3omc i/o and motor conversion to mercruiser

Lou--

Any "Gen 2" drive can be modified. The modification is simple, not even requiring that the drive be disassembled. However, the measurements are pretty critical and any variation can potentially cause issues. Having SEI do the modification preserves your warranty and ensures that the dimensions are correct.



If you can get service for your drive, an investment like this doesn't make a lot of sense, until you need a new lower unit or whatever. The Cobra is a great drive (better than the Alpha, IMO)

There's still a lot of very nice Cobra-powered boats out there and this gives their owners a choice when it comes time for a new drive.

Fair winds,

Chris

thanks for the info Chris...that gives me food for thought...when the time comes...I'll have to decide what's the best course of action...For now the Cobra is doing fine....I had my mechanic fix the shifting problems 5 years ago and all I've done since has been maintenance (bellows...gimble...trim lines) this boat is slipped in salt water 6 months of the year so it gets a lot of marine growth and looks pretty nasty but it works fine...if the transom assembly and trim rams are stil OK when the time comes...the conversion would make sense...but if corrosion is a problem by then (always a possibility with a sterndrive in salt water) then a complete conversion to Merc would make more sense....

BTW I have an older FW as well...they are solid boats...this one needed a deck replacement...I put it back together better than it was originally...the hull design was good enough to make it worth it in terms of ride and stability...hope to hold onto it for a long while if I can...

 

[vdomt]

Re: 4.3omc i/o and motor conversion to mercruiser

the sei conversion looks like the way i'll go but i'm not sure what gear ratio i need. i found one web site that said the omc 4.3 was 21/19 but i'm not sure that it's really what i have. is there some way i can find out what i have? If not what would some of you more knowledgable folk suggest? my boat is a heavy 7000 plus lb cruiser. i'm running 15/15.5 props and turning 4400 plus rpms. i have to run about 3800rpms and run about 27mph otherwise it seems to plow alot. i'd like to be able to cut the rpms some and still get the 27mph but don't know that i have enough power to increase gear ratio or if it's even an option.

 

[Ducatinut]

Re: 4.3omc i/o and motor conversion to mercruiser

the sei conversion looks like the way i'll go but i'm not sure what gear ratio i need. i found one web site that said the omc 4.3 was 21/19 but i'm not sure that it's really what i have. is there some way i can find out what i have? If not what would some of you more knowledgable folk suggest? my boat is a heavy 7000 plus lb cruiser. i'm running 15/15.5 props and turning 4400 plus rpms. i have to run about 3800rpms and run about 27mph otherwise it seems to plow alot. i'd like to be able to cut the rpms some and still get the 27mph but don't know that i have enough power to increase gear ratio or if it's even an option.

According to my OMC shop manual, you should have a 1.68:1 gearset. The closest thing to what you want is the 1.62:1. You could go to the 1.81:1, but I don't think you'll be able to prop it right. There's also the possibility of overheating the upper gears (don't ask me how I know) by dropping to a gear ratio that's too low.

Prop choice is more art than science. Every hull is different and everyone has a different opinion on what is acceptable (bellybuttons, etc). Use one of the many prop selectors (pretend like your boat already has a Merc on it) on the web to get close and find a reputable prop shop to work with. Our local shop will work with you when selecting a prop, basically, giving you the purchase value of your prop in credit if you trade for something different.

Good luck to you with your conversion - I think you'll be very happy with it. I was very pleased with the quality of the pre-production parts that I installed on my boat. First class stuff.

Fair winds,

Chris

 

[Ducatinut]

Re: 4.3omc i/o and motor conversion to mercruiser

thanks for the info Chris...that gives me food for thought...when the time comes...I'll have to decide what's the best course of action...For now the Cobra is doing fine....I had my mechanic fix the shifting problems 5 years ago and all I've done since has been maintenance (bellows...gimble...trim lines) this boat is slipped in salt water 6 months of the year so it gets a lot of marine growth and looks pretty nasty but it works fine...if the transom assembly and trim rams are stil OK when the time comes...the conversion would make sense...but if corrosion is a problem by then (always a possibility with a sterndrive in salt water) then a complete conversion to Merc would make more sense....

Lou--

The Cobra is a great drive if you (or someone else) knows how to take care of it. I've had Alphas and Cobras apart on my bench and the Cobra is the superior product (they had the advantage of learning from Merc's designs), but they can be a finicky devil to work with.

The transom parts on the 4-cyl boats are the same as the big blocks and are wickedly overbuilt. I've looked at a couple of Volvo SX setups and it looks like Volvo basically just carved their name into the OMC castings. That's a HUGE compliment to OMC, in my opinion.

I love my Four Winns, too. It's a traditional big water hull, solidly built and still gets compliments at the dock. Everything in the boat works (just shy of 700 total hours, 200 in the past 2.5 years), it starts every time, and handles easily for noobs and more experienced folks alike. The deep hull makes for a nice ride and I always seem to have a wakeboard boat or two in my stern wash looking for a smooth ride in the mid-afternoon chop...

Fair winds,

Chris