Using a 2.0 gear ratio lower unit on a 200HP Mariner

[powrguy]

What problem would there be by using a 2.0 lower unit on a 2.4L Mariner 200 (1986) that could not be accomodated for with a prop change to a different pitch? The bad lower unit on it now has a 1.87 ratio, and it seems that going to 2.0 should not be that big a problem.

How about DukeDog?

 

[Yepblaze]

Re: Using a 2.0 gear ratio lower unit on a 200HP Mariner

You would need to re-prop it, and to do that might require more than one prop purchase till you find which new prop will now work best for you.

 

[powrguy]

Re: Using a 2.0 gear ratio lower unit on a 200HP Mariner

You would need to re-prop it, and to do that might require more than one prop purchase till you find which new prop will now work best for you.

As I understand the concept, a 2.0 ratio means the engine turns 2.0 rev's per 1 rev of the prop shaft, right? If you changed the prop to get nearly the same ratio change (approx. 7% changed), you could go from a pitch of say X, to a 1.07X (16 to 15 pitch, for example) and get the WOT to be the same? Or am I missing something? I know the reason for the ratio difference in the higher output motors is to accomodate the range of props to achieve correct WOT with a given power output, I think, right?

 

[Faztbullet]

Re: Using a 2.0 gear ratio lower unit on a 200HP Mariner

Using a 2.1 ratio on a 200 will do the following with the existing prop:
1) Faster hole shot
2) Around 450 more rpm on top end
3) Will allow you to possibly go up one pitch size and maybe pick up 1.5-3 mph on top end.

When I used to hot rod and race we used the 2.0 unit with the reverse gear teeth ground off (smooth gear),C-130 full synthetic turbo prop shaft fluid and only 16 oz of fluid, this was good for 1000 rpm on top end.

 

[powrguy]

Re: Using a 2.0 gear ratio lower unit on a 200HP Mariner

Using a 2.1 ratio on a 200 will do the following with the existing prop:
1) Faster hole shot
2) Around 450 more rpm on top end
3) Will allow you to possibly go up one pitch size and maybe pick up 1.5-3 mph on top end.

When I used to hot rod and race we used the 2.0 unit with the reverse gear teeth ground off (smooth gear),C-130 full synthetic turbo prop shaft fluid and only 16 oz of fluid, this was good for 1000 rpm on top end.

Whew....you were screamin', then !

As I understand it, the bottom-line is I probably won't have to do much of anything with the ratio changed, and the performance MIGHT have a better hole shot, with a bit less top-end speed, then?



thanks

 

[Faztbullet]

Re: Using a 2.0 gear ratio lower unit on a 200HP Mariner

Tou are correct, if you was only turning 5500rpm this will put right @ 6000 which is ok. You can then run a little xtra weight or livewell full of water or have prop double cupped for some extra lift.

 

[Dukedog]

Re: Using a 2.0 gear ratio lower unit on a 200HP Mariner

Pretty much "right on" in above posts. Tha only thing I would add is that, dependin' on your motor height, ya might get a little more ventilation comin' outta tha hole. Tha 2 ta 1 will spin it up quicker. Extra cup would probably tame some of it though. But I like "ventilation"................

 

[Texasmark]

Re: Using a 2.0 gear ratio lower unit on a 200HP Mariner

I'd make the change in the lower unit and look at your performance numbers. You are only looking at a 11% change in propshaft rpm's. 11% on a 20P prop is 2.2 inches, noticeable on some boats, but maybe not that noticeable to you or just maybe you will like the performance better than what you have now. One thing is for sure: the engine (powerhead) will love you for it and you may pickup a mile or two per gallon. Also, unloading the engine may allow for rpm's to increase more than the 11% ratio which would make the prop spin faster and reduce your 11% difference.

Mark