Going from 1.32 gear ratio to 1.47 on 7.4L Mercruiser Searay Sundancer 268DA

[pessemist]

Need to do a full outdrive replacement on a 7.4L Mercruiser Searay Sundancer 268DA.

Originally had 1.32 gear ratio but the only affordable option seems to be the 1.47.

My question is it smart to attempt to use the 1.47 ratio on this heavy boat? I use a drive shower & synthetic lube.

The original prop was an aluminun 15.25x15. I think with the new 1.47 gear set I can go up one pitch size to 15.25x16? And get near the same performance?

I should say I baby this boat and seldom go WOT and always roll on power gradually. I know this engine eats the Alpha 1's.

I just want to know if this drive ratio change will result in serious problems with performance and/or with strain to the gears & shafts spinning a higher pitched prop?

[admin]

That particular engine is hard on the drives, but it sounds like you drive it with that in mind. Our warranty doesn't cover it with that engine, but alot of people use them. I would guess you probably will need a 17 pitch, but a 16 may work.

Tech Support

[C.Deese]

Im sure you have gotten an answer to your question already however im new to the forum because i didnt even know about it until the other night. After reading for several hours ,I realized there's a lot of information in the answers to a lot of good questions. These type forums are extremely helpful to the DIY'ers an for those who are intrested in just knowing a little more of how systems on their boat are supposed to work. This particuler post caught my attention with that odd 1.32 ratio question. The 1.32 upper gear sets were mainly for the high perf boats with 454's ,350 mag's etc. Only used for v-8 witch most came with 1.50 ratios. The difference between the 1.32 an the 1.50 was that they were very heavy duty with a lot more meat to handle the higher HP. Also these gear sets were installed in the gen 1 an i think the earlier MR drives might have used them. Im pretty sure the 1.47 gears wont work in this drive that you have. 1.47's are used in gen 2 drives. Nowadays boats with high perf eng's come with bravo units. Im glad i stumbled across this forum , SEI drives are built tough. I've installed quite a few an never had an prob. Good luck to ya mr. Pessemist. I like that screen name , Im one too. LOL

[kwagner]

Pessemist,
I have a "87" 268DA, and looking at the same solution that you chose. I, like you take pretty easy when rolling on the throttle, no hole shots, very seldom WOT ( only when the water is like glass). So, I was wondering how the 1:47 gearing is working out for you? thanks

[pessemist]

Just saw your post kwagner-

So far so good. I have about 50 hours on the stern drive unit and, so far, it has worked flawlessly, I did go through the break-in procedure exactly as prescribed. Right now I am turning a 16 pitch prop which is not enough as the engine can over-rev by about 200 rpms (4600 vs 4400rpms). I will soon switch to a 17 pitch prop which should be perfect.

I swapped out the lube after break-in and noticed no metal filings. I do run a drive shower and always roll on the power slowly and as smooth as I can.

Some research shows that the 268 Sundancer came with the 1.32 gear ratio. Basically that meant the two top gears in the upper case not only turned the prop a little slower but were far beefier than the 1.5 or higher ratio units.

This allowed them to handle the extra horsepower of the 7.4 liter big blocks. Even so, those engines could tear up the Alpha drives (especially with the shock of high performance boats hitting waves and allowing the sterndrives to take a pounding as the prop came up and then bit down again.

Failure of the Alpha's with big block engines was the primary motivator for the development of the Bravo drive which was much beefier. Our 268 Sundancers were only fitted with the Alphas for a couple of years (87'-88') before they were then built with the Bravo's.

At 4400rpms I can hit 33mph. But I try and stay near 3500-4000rpms and cruise around at 24mph.

I'll post back with eprformance numbers after I swap out to a 17 pitch prop.

[kwagner]

Pessemist,
I finally blew up the original 1.32 alpha, and was wondering how this has worked out for you? What prop did you end up going with?
thanks