Transmission and gear ratios

[ericmuhlbauer]

So ive installed an 18hp motor onto an old yerf dog 3002 that used the Tecumseh 6.5hp. im needing to build transmision to handle the torque from this powerful engine. The original trans was a 30 series comet torque converter but im thinking of switching to a centrifugal clutch to avoid using a belt. My question is if i bought a 14tooth clutch and connected it to a say 9tooth sprocket on the jackshaft and also installed say a 36tooth sprocket to the jackshaft to connect to the drive gear on the axle would that decrease my gear ratio? Because a 14-9t would be a 1.6 and a 36-60t would be a 1.5...is that correct? or am i underthinking this?

 

[landuse]

That would give you a ratio of 2.4:1. Not going to happen!!!

That is far too high, no matter what the size of your engine. I would ditch the 36 for something smaller, like half the size

 

[ericmuhlbauer]

Ok on a centrifugal clutch can the sprockets be switched out for something bigger to try and avoid using such a big gear on the jackshaft?

 

[PredatorPowaaa!!]

i don't think most centrifugal clutches will handle that kind of power. i would go with a 40 series torque converter or somthing better. only downside is that they are expensive.

 

[ericmuhlbauer]

I've found some centrifugal clutches that claim to be able to handle an 18hp motor...Also from what I can tell the belts that come with the 40 series torque converter are too long to fit my setup and having already mounted the motor if rather not have to rework the frame to fit a longer stronger belt

 

[Kartorbust]

40 series is not going to last long enough, only rated for 16hp at most. Look at a Duster or a 780 comet. A CVT will be way better and won't burn up like a centrifugal would.

 

[PredatorPowaaa!!]

But the dusters are expensive... If only they had lots of cheap knock offs like the 30 series

 

[ericmuhlbauer]

Duster? I'm not familiar with that...Link?

 

[Kartorbust]

Here ya go http://beltpalace.com/comet206095a.html

 

[ericmuhlbauer]

Does that just replace my driver pulley or do I need to buy another driven pulley to accommodate the wider belt?

 

[Kartorbust]

Have to buy both the driver and driven.

 

[OzFab]

As most have suggested, a TC Is the better option but, if you insist on using a cent clutch, you need to:
1. reverse the sprockets on the J/S (9 tooth out, not in)
2. use a 20t as opposed to a 36t...

With the 14t clutch & 60t axle sprocket, this will result in a 9.5:1 gear ratio...