Outdrive Ratio - moving up

[Archnawan]

So I've decided to go ahead and replace my leaking outdrive but I'm not sure what ratio is on it now. I would like to move up to the next ratio because even with a 15" pitch stainless prop I can only get about 4300 rpm and thats with almost empty gas tank, no water, and only two people. <br /><br />The only thing on the drive is <br />" OD7300 " <br />Not sure if this means anything and couldn't find anything about it. Anyone know?

 

[Bondo]

Re: Outdrive Ratio - moving up

What Outdrive ????<br />What Engine ???<br />Build By Who ???? <br />

I would like to move up to

Actually,........ You want to go Down in Ratio..........<br /><br />That means a Higher #.......

 

[Bob_VT]

Re: Outdrive Ratio - moving up

My engine operates best at 4200-4400 rpm. What motor is in your boat? What's the weight? That might be all you can get.

 

[Archnawan]

Re: Outdrive Ratio - moving up

Its an alpha one gen two on a 95 bayliner 2655 with the 5.0LX. Specs say it should have 1.5 but I'm not sure what it really has because the previous owner replaced it after a run-in with a stump.<br /><br />I am assuming it a 1.5 ratio means that the drive shaft out of the engine turns 1.5 times for the prop to turn once, so if I go up to the 1.62 it will give more torque at the prop.

 

[Bondo]

Re: Outdrive Ratio - moving up

Ayuh,........ If you go Down to the 1.62/1 you'll Gain about 2 1/2"s of Prop Pitch........<br />The 1.84/1s will yield about 5 1/2" to 6" of Prop Pitch.........

 

[Bt Doctur]

Re: Outdrive Ratio - moving up

unless the drive has 1.32-1 gears in it now. these were used on light boats with big block chevys.

 

[MrBill]

Re: Outdrive Ratio - moving up

If it's junk...open it up and count the gear teeth to determine the actual ratio and decide your next move.

 

[Don S]

Re: Outdrive Ratio - moving up

Just remember one thing. Your engine needs to be within certain specs for WOT rpm. Too low an rpm and you are overloading the engine, to high an rpm and you loose top end speed.<br />You have a 26 foot boat with a 5.0L engine, changing gear ratio's is not going to be a increase torque from the engine, and that is where the torque comes from.<br />If you are getting the proper WOT rpm with your prop and it's in the 19 to 21 pitch range, you are at optimum everything with the 5.0.

 

[Bondo]

Re: Outdrive Ratio - moving up

Don,......Read his 1st post........<br /><br />He's at the Bottom of the range of available Props............<br /><br />Jumping Down to the 1.65/1s, or the 1.84/1s will put him into the range of Usable Prop Pitches......<br /><br />If he Now has 1.50/1s............

 

[Archnawan]

Re: Outdrive Ratio - moving up

MrBill, lower is bad, top drive is fine so I hate to open it up just to count gears. <br /><br />The motor runs great and just got new plugs, fuel filters, oil, etc. so I think I'm getting all the power I can from it. Basically once I get on plane with full throttle I will hit 4000 fairly quick, from there depending on load and water condition I will climb slowly to somewhere under 4300. Avg day I'd say I top out closer to 4200. <br /><br />Bondo, I'm sure you know much more about this than I but for my 15" prop if I assume I have 1.5 and I get 1.62 wouldn't the math go<br /><br />1.5/1.62 x 15 = 13.6<br /><br />I would take this mean that going up to the 1.62's would give a 13.6" equivalent prop using the same 15" prop I have now. Further assuming that 1" pitch ~ 200 rpm give about an extra 300 rpm. 4500 - 4600 top rpm sounds pretty good to me if this is the case.<br /><br />Thanks again for all the help and suggestions!!

 

[Bondo]

Re: Outdrive Ratio - moving up

Well,........<br /><br />I was Never a Mathematician,.....And I guess Your formula of it is about Right.........<br /><br />If you use a 1.62/1 ratio drive,... It Should Equal about the Same Engine RPMs,.. with a 17" prop,......<br />As the 1.5/1 ratio with the 15" Prop..........