Transmissions and gear ratios

[RAWicklund]

Well I've got my engines ( Steyr MO256) 240hp now I need to match up some transmissions.

Doing a site search.... My 1st choice is a zf45A 8 degree down angle. 2-1 ratio.

This choice was divined from consensus of the site search.. not math.

I'm comparing the Steyr's to the Yanmar 6's.

I would prefer the 45a's over the 63a's due to a 35lb. weight differance.
Does it matter?Does anybody here run the 63a's? Any problem with the size?

Same preferance and reason over the Twin disc 501's.

Anybody out there have any opinions on a better choice??
Thanks
Ray

[Kevin]

Ray,
I forgot to tell you I have the 1.5 ratio. Bone stock running gear.

The MO256K43 has 250 Hp and 450 torque.
The MO256H45 has 250 HP and 500 torque.

The variation in power is due to the turbo style and size. KKK Vs Holset I think.

My old MO236K43 are 212 HP and around 350 torque if my memory serves me correctly. They raised the HP to 230 after I bought mine.

It would be great if you could stick with the same gear I have but the torque may be too high on yours.....not positive though.

[Bruce]

The weight difference will not matter.
Normal gear ratio for that HP range would be a 2:1 in a 31 in most anything over a 3k rpm.

Other boats may not have the prop clearance to run a 2:1. the other issue is running gear expense.

Some 28"s have 1-1/8 shafts who's safety twist rate can be close or under the recommended margine using 2:1 ratio without the expense of replacing the running gear to larger diameter shafts.

I've used the 45's on small block gas. I myself would use the 63.

[scenarioL113]

I have the 45a's in my B28. I am only running 150HP Cumins 4BT's. I think the 240HP you are running would be maxing the rating on the zf45a's.

Double check the specs. The 45a's sure are light though. I installed them by myself by hand with not too much effort.

[RAWicklund]

Thanks for the input.

I delayed getting back to reply since I was waiting on a deal to go thru on (1) zf63a.

I don't have possesion of the gear yet, but the deal is agreed on and my check is in the mail.....$1350 for a factory rebuild w/warranty.
Still in the market for 1 more... but not in any hurry.

ZF's internet site has an engine matching calculator that claims the 45a is a good match. But the customer rep. echoed the advise from others about the 63a upgrade.

One of my biggest concerns was available space.... but that concern seems unfounded now.

Kevin... I'm sure I'll be picking your brain in the future.

Once again, I'm not in a rush to start this repower project. I want to at least be ready to hang a "For Sale" sign on my B28. Before I start on the 31 again.

Thanks again for all the input.

Ray