what is the correct ratio

[betayv]

hello there 1995mercruiser with a 305 engine and a alpha gen II outdrive what is the correct ratio for the outdrive thanks.

 

[Don S]

Re: what is the correct ratio

1.47/1.50

 

[betayv]

Re: what is the correct ratio

thanks a guy was trying to sell me a 1.63 I know that wasnt the right one thanks again.

 

[betayv]

Re: what is the correct ratio

ok this guy just send me this email please let me know what you think

Here is a copy of the chart I mentioned, as you can see, a 305 should use a 1.61 ratio (or a 1.65 which was the earlier ratio). The drive I have is for a V6, and has a 1.81 ratio (or a 1.84 which was the earlier ratio). You'll note that the horsepower of the 4.3L V6 and the 5.0L V8 are not tremendously different. As a matter of fact, the newer 4.3L Vortec motors were 205HP and used the 1.81 ratio drive.

Moral of the story, I think the drive that I have available will be just fine for you, you can always adjust propeller pitch once the boat is assembled to achieve optimum all around performance.

mercruiser Alpha 1 Gen 2 (1991 & Newer)
Engine HP Liters/CID Cylinders Gear Ratio Tooth Count Year
3 Liter 130 3.0/181 4 2.0 24-24 1998-2005
3 Liter 130 3.0/181 4 1.94 20-24 1991-2005
4.3 Liter 175 4.3/262 6 1.81 17-19 1991-2005
5.0 Liter 230 5.0/305 8 1.61 24-24 1991-2005
5.7 Liter 260 5.7/350 8 1.47 20-22 1991-2005

 

[wca_tim]

Re: what is the correct ratio

depends on what you really want. either should be fine to be honest. with the 1.6 you'l lhave a little more torque and can turn a bit more pitch prop. The boat will more than likely be a couple mph faster also.

Note that some of the newer fast boats are coming out with 1.6 ration bravo drives now... It gets you into a little more efficient range of props... IF you reprop appropriately. the difference in 1.5 and 1.6 is only a couple of inches prop difference, but does give you a good bit more torque...

Note that the same is true but even more with a 1.8 - the ratio I had on my v-8 until recently. It made a good bit of (positive) difference...

 

[JustJason]

Re: what is the correct ratio

everything you need to know about sterndrive ratios.... Courtesy via me.

http://www.4shared.com/file/113521134/81eff60b/sterndrive_ratio.html

 

[180shabah]

Re: what is the correct ratio

1.6 is good for a carbed 305(or an injected 4.3vortec). What ratio do you have now?

 

[wca_tim]

Re: what is the correct ratio

have had a lot of discussion about this online and off and have been playing with my own boat and others. more mechanical reduction will wind up making most boats faster as long as prop pitch doesn't have to go over something like 30. the exception is a tug boat. I've also now had 4 different gear ratios on my one boat with the same engine and with each propped with a good quality stainless prop with pitch appropriate to put wot about the same place.

1.81, 28" mach sterndriver = fastest by a good bit, great holeshot

1.65, 26" turbo or hydromotive quad iv = second fastest, good holeshot

1.47, 23" laser 2 = slowest, worst holeshot by far

1.32* 21" laser, 21' solas, close to fastest with the laser. fair holeshot

*caveat is this is an alpha one ss drive, cle gearcase and closer to the surface. I'm pretty sure that the same trend above will apply once I swap the 1.32 gears to 1.65. I won't go with the 1.8 because I'm pretty sure that even a 30" prop will put wot rpms higher than I want them.

wy does merc put 1.47 gears behind all the v-8s? because one size has to fit all. Unfortunately that means that it is a comprimise in most situations and smaller recreational boats pay a good bit of performance in order that the same drive will work on big cruisers....

something to think about... imho

 

[180shabah]

Re: what is the correct ratio

wy does merc put 1.47 gears behind all the v-8s

They don't, mercs website lists 2-3 ratios for each engine. The final decision is entirely up to the manufacturer of the boat.

 

[wca_tim]

Re: what is the correct ratio

They don't, mercs website lists 2-3 ratios for each engine. The final decision is entirely up to the manufacturer of the boat.

sure.. but far and away the most common ratio behind a v8 is 1.50 / 1.47 - to the point where most people assume right off the bat that it's the only right ratio for a 305 or 350. It's certainly the answer on here every time someone suggests going from a v-6 to a v8....