Got A NEW Toy!!! OMC ->> Merc Swap??

[Celebrity240]

Hi guys, i just got a new toy, '95 Chris Craft Concept 27ft. I got it at an auction, and its missing the motor and drive, otherwise in pristine condition. It is supposed to be a OMC 7.4L.... Im not a big OMC fan, all my boats always Merc, had one OMC before and I wasnt too lucky with it.

QUESTION:

Is it going to be a problem changing the Transom Assy?? Bolt on/ Bolt off??

What would be some challenges I would face with this swap, considering the only OMC part still on the boat is the transom. Will the motor mounts be an issue... since i believe they are both still same 454 blocks right? Short or Long??

Thanks!!

 

[Don S]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

Being a 95, we need to determine exactly which outdrive you have. It's VERY possible you have an SX Cobra which is actually the Volvo outdrive, and not the old OMC dog clutch outdrive. Do you have an pictures of your drive?

 

[Celebrity240]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

no drive, no motor, only the transom assy, so starting fresh

 

[Don S]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

no drive, no motor, only the transom assy, so starting fresh

How in the heck did I miss that in the original post.:redface: :redface: :redface:

The cutout is the same as the Mercruiser. Remove the OMC, install the Mercruiser.

 

[Celebrity240]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

Originally its suposed to be a king cobra I beleve

 

[Celebrity240]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

Ok perfect, so how about for the block, will the mounting holes line up? 7.4 omc and 7.4 merc should be the same block right?

 

[wire2]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

Yes. OMC or Merc 7.4 (454) are the same GM block. But I believe the transom assembly is different, so you'll need to get Merc transom assy, gimbal assy and leg.

 

[HT32BSX115]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

Ok perfect, so how about for the block, will the mounting holes line up? 7.4 omc and 7.4 merc should be the same block right?

Howdy,

Your engine mounts may not be in the same place on the mounting blocks in the floor so you may have to fill in the lag-bolt holes and drill new ones.

You'll also need to drill 2 additional holes at the top of the "cut-out" to accommodate 2 additional studs in the Bravo transom mount.

You should be able to use the existing steering cable and helm.

With a boat that big, you'll probably want to find a 454/502/496 mated up to a 2.00 or 2.20:1 ratio Bravo III.

It'll be an easy install. I pulled my previous OMG 460 King Kobra and replaced it with a 1997 454 & 1.81:1 Bravo III. I was lucky, I found the engine and drive (everything) for about $5K and I was able to sell all my OMG junk piece by piece for about $3500!


Good luck !!


Rick

 

[Bondo]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

Ok perfect, so how about for the block, will the mounting holes line up? 7.4 omc and 7.4 merc should be the same block right?

Ayuh,... You're changing to All New, the bolt holes won't matter...

 

[Celebrity240]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

5k? wow good deal, i hope i get as lucky as you did. Why 2.00, 2:20, i was thinking 1.50?? The boat is still a more or less a cuddy, it pretty shallow, not that heavy just long.

Howdy,

Your engine mounts may not be in the same place on the mounting blocks in the floor so you may have to fill in the lag-bolt holes and drill new ones.

You'll also need to drill 2 additional holes at the top of the "cut-out" to accommodate 2 additional studs in the Bravo transom mount.

You should be able to use the existing steering cable and helm.

With a boat that big, you'll probably want to find a 454/502/496 mated up to a 2.00 or 2.20:1 ratio Bravo III.

It'll be an easy install. I pulled my previous OMG 460 King Kobra and replaced it with a 1997 454 & 1.81:1 Bravo III. I was lucky, I found the engine and drive (everything) for about $5K and I was able to sell all my OMG junk piece by piece for about $3500!


Good luck !!


Rick

 

[HT32BSX115]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

5k? wow good deal, i hope i get as lucky as you did. Why 2.00, 2:20, i was thinking 1.50?? The boat is still a more or less a cuddy, it pretty shallow, not that heavy just long.

Hmm, Are we talking about the same boat?

Length: 27′ 0″
Beam: 9′ 0″
Draft: 2′ 10″
Weight: 5000 lbs
Fuel tank size: 80/97 gallons
Water tank size: 20 gallons
Hull type: Deep V
Deadrise: 20 degs
Production year(s): 1992 - 1996
Engine options: Single Stern Drive Gas 310 hp Volvo
Cruise Speed: 25 mph






27ft is a pretty good size boat. (5000+lbs.....probably 6000lbs with twins)

You might do it with a Bravo I but it's going to be somewhat slow out of the hole and it's going to have a LOT of slip accelerating and at cruise speeds. I would only install a Bravo III or Volvo DP. A boat that heavy would want either twins or a dual counter-rotating prop drive.


I did a little google search of other Concept 27's. They made a LOT of them with 250+hp twins or BB VP Duoprop installations.

They seemed to rate the cruise speeds at less than 30mph and top speeds around 35-40....


Even with a 2.20:1 Bravo III ...........24P props might be over propped with a carbed 454.

 

[Celebrity240]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

hmmm... ok maybe i should look into getting a 502 in that case......?

 

[Celebrity240]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

Hey i just tought of something, i got 2 350's sitting beside my house with all accessories, if i get the 454 block by itself, will the accessories work from the 350's??

 

[Bondo]

Re: Got A NEW Toy!!! OMC ->> Merc Swap??

if i get the 454 block by itself, will the accessories work from the 350's??

Ayuh,.... A Few, but Very few...