Out drive gearing questions

B

Bubba1235

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Ok, so I look at how out drives are geared and to be honest I am confused. (Nothing new in that.) It seems as though everything is set up so the engines max RPMs are in the 4400 to 4800 RPM range. So my question is, what about an engine that can safely run at higher RPMs? As an example say a Chevy LS-1 (350) that has a read line around 6200 RPM and develops lots of ponies above 4500 RPM?

Is there a reason the outdrive manufactures don't want these higher RPMS? It seems a bit strange to me that you would gear it to the point it can't spin that fast and then put a steeper prop on the drive.

Help me out of this confusion...
 
Bondo

Bondo

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Re: Out drive gearing questions

As an example say a Chevy LS-1 (350) that has a read line around 6200 RPM and develops lots of ponies above 4500 RPM?
Click to expand...

Ayuh,.....

The Outdrives are geared to match Common Marine Motors.....

The LS-1 you're asking about Isn't at All a motor set up for Marine Service......
 
Don S

Don S

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Re: Out drive gearing questions

The gear ratio has nothing to do with keeping the engine rpm down, it has to do with keeping the props in a certain range for most efficient use.
Props in the 17" to 23" pitch is where you get the best hole shot and cruse speed. Plus, that is where most of the props on the market are.
With engines of different torque specs are used, they need different gear ratios to use props in above ranges.
 
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CharlieB

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Re: Out drive gearing questions

HP is a measurement most applicable to maintaining speed.

Torque is the measurement of the ability to do work.

Load is work, turning a prop is doing serious work.

Don is correct that a prop is designed to work best within an RPM range.

Marine motors are designed to operate near peak torque, gearcase ratios are designed such that prop RPM falls within the RPM range of the prop AND that prop size and pitch provides just enough load on the engine to hold engine RPM at WOT near peak torque of that engine.

Clear as mud, isn't it?
 
1

1976 Slickcraft

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Re: Out drive gearing questions

Another thing to think about is more RMP`s builds more heat in your gear case.
Jesse
 
Don S

Don S

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Re: Out drive gearing questions

It doesn't matter what rpm the engine was designed to handle, the problem is when the torque curve ends. You may have 500 hp at 8000 rpm, but if the torque gain quits at 3000 rpm, in a boat, that's where you stop gaining rpm.
 
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