Converting Penta SX to Mercruiser Power need advice

I have the opportunity to buy a late model boat that the motor was pulled out of. Dont know the exact motor, but the outdrive is a Volvo Penta SX.
I have a fresh Mercruiser 898 305 V8 that is sitting in my shop waiting for a hull. Sounds like a great opportunity but am unsure of what will be required to make the Merc mate up to the Penta. I also have access to a late model Alpha One complete outdrive so I could just go with the A1, however I know that the Penta is a much smoother drive.
Here is what I know I will need and please throw in your input and advice. I really appreciate it.
Bell Housing
Flywheel
Coupler
Possible new starter to match the flywheel
Fresh water pump?? (read something about that somewhere)

All input appreciated.
Dane

Re: Converting Penta SX to Mercruiser Power need advice

Use the Merc coupler and the original flywheel and starter.
The bellhousing is also the same thing as the OMC Cobra housing.
Raw water pump (not fresh water pump), you can get a crankshaft mounted pump. Volvo used them for years on the 5.0 and 5.7's, and you can even buy the pumps from NAPA. Wiring harness plug should hook up with no problem.
Exhaust manifolds and risers will need to be the Volvo/OMC Cobra style to match up with the exhaust Y on the transom shield.

The bigest problem with this swap is not knowing what came out of it.
You do need to know the gear ratio. Do you see any model numbers or Volvo serial numbers on anything?
Do you have the exhaust y mounted to the transom shield

Re: Converting Penta SX to Mercruiser Power need advice

Bubba1235 said:

Pardon my asking but,,, why would you get rid of the best drive made in favor of a Mercruiser?

Click to expand...

I guess cause I am not sure how much of a pain in the rear it will be to connect that drive to my merc motor. I will keep it if I can.

Re: Converting Penta SX to Mercruiser Power need advice

I have no past experience with VolvoPenta motors or drives. Did they always use OMC/Cobra motors and is OMC/Cobra always based on GM block?
The exhaust Y is there. It is a SX-M with a 1.60 ratio. I have the serial number if that will help. So really all I need is the Bell Housing from an OMC/Cobra or Penta for GM V8? THe merc has risers and was hoping I could re-use those and just put new bellows on, but I guess I need to look at a pic of the two risers side by side to see the difference. The exhaust risers will be the most costly part of this swap...
Thanks for the help!

Re: Converting Penta SX to Mercruiser Power need advice

Volvo went into a joint venture in 93. In 98 the bought them out completely. OMC no longer exists. BUT, VP used the Cobra transom shield, bell housings, and kept the overall OUTSIDE appearance of the outdrive till around 2006.
Then that changed also
Many of the parts fit from the Cobra. The trick is, to know the difference. I do this for a living and used to be a Volvo certified tech before moving here.
The 1.60 ratio is the ratio for a small block Chevy engine. You lucked out.
Even if the manifolds are expensive, you have a great drive. In the future you can also replace just the lower unit to make DP drive out of it. You will never believe the difference that will make.

Re: Converting Penta SX to Mercruiser Power need advice

Thanks for the History and info!! Do I need manifolds or just the risers?
Would the DuoProp require more HP than my little 305 could give it? I would love to have the DP!
So just to clarify, I need to get the following parts:
Raw water pump
OMC/Cobra Bell housing
OMC/Cobra Exhaust Risers and bellows.

Thanks!

Re: Converting Penta SX to Mercruiser Power need advice

You will need manifolds, and risers, and probably some thermostat housing changing and rethinking. Changing from one engine style to another isn't always obvious and you could run into a bunch of unknown problems along the way.
Get it all running with the SX (single prop) first. The DP is also used with a 4.3L carbed engine, not a problem. But don't put the cart in front of the horse at this point.
You need to get an engine in there and working first. Then upgrade if you need/want/can afford to.

Re: Converting Penta SX to Mercruiser Power need advice

Thanks again. I found a complete manifold and riser kit with gaskets on ebay for $419. and an OMC bell housing for $100. Not too bad. So the Merc coupler will work for me? Someone told me I would need a different coupler, but he also told me I would also need a flywheel... You have the edge on experience thats for sure.
Let me know if you ever need a good deal on props. I will hook you up. My brother owns PowerTech

Re: Converting Penta SX to Mercruiser Power need advice

I don't know exactly if the coupler will fit or not. The splines will be the same, but I have no idea if the depth of the coupler is the same as the Cobra or not. But at 300+ dollars It might be forth finding out. They look about the same after seeing both, I just never put them side by side to check. Maybe you could find a marine store locally where you could compare them.