Can I get some suggestions for an appropriate gear ratio?

[scottbahl]

The kart show in the pic is about 120lbs.

The engine I am going to be adding is an 11 HP, 4-stroke 340cc Blue Max engine.
The no-load speed is 3600RPM and the idle speed is 1400RPM.
Engine weight is 80lbs.

Rear wheel diameter is 16".


What gear ratio would you guys recommend for this setup? I will most likely be running this kart on dirt lots and pastures, and maybe up a moderate incline.

-Scott

 

[crazykart]

Well first most.of us would suggest a TC instead of a.clutch for many reasons, offroad, tire size, engine size, and TC's are generally better.

With 16" tires I would say something along the lines of an 8:1 or 9:1 ratio should be good especially with a tc.

 

[itsid]

Well that's 200lbs in kart.. what about the driver ?

Is it safe to assume, that he (you in this case) is no more than that?
so we can limit the calculations to 400lbs or less?

well then:
centrifugal clutch:
Recommended ratio 8.5: 1
with a #40 chain that's a ten tooth clutch and a 85T axle sprocket!

here's why:
KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 40.64 cm | 16 in[/B]
[I]Total weight[/I]: [B] 181 kg | 399.04 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 11[/B]
[I]Asummed HP[/I]: [B] ~11[/B]
[I]Torque[/I]: [B] 21.76 Nm | 16.05 ft lbf[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 8:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 174.08 Nm | 128.39 ft lbf[/B]
[I]Acceleration[/I]: [B] 4.73 m/s² | 15.52 ft/s²[/B]
[I]Top Speed[/I]: [B] 34.47 km/h | 21.42 mph[/B]
[/INDENT]
[B][U]PROBLEMS[/U][/B]
[INDENT][B]You might burn your clutch/belt![/B]
[B]Gear ratio too high![/B]
[I]Suggested final ratio[/I]: [B] at least 8.1:1[/B]
[/INDENT]
[/FONT]

so even a small inclination might ruin your clutch.

KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART & ENGINE[/U][/B]
[INDENT][B]As above[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 8.5:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 184.96 Nm | 136.42 ft lbf[/B]
[I]Acceleration[/I]: [B] 5.03 m/s² | 16.5 ft/s²[/B]
[I]Top Speed[/I]: [B] 32.44 km/h | 20.16 mph[/B]
[/INDENT]
[/FONT]

So I'd recommend a series40 Torque converter...
simple reason:
with a 5.5:1 ratio you have much better clearance and much better top speed...
while still adding 100Nm to take off
KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 40.64 cm | 16 in[/B]
[I]Total weight[/I]: [B] 181 kg | 399.04 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 11[/B]
[I]Asummed HP[/I]: [B] ~11[/B]
[I]Torque[/I]: [B] 21.76 Nm | 16.05 ft lbf[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 5.5:1[/B]
[I]TC type[/I]: [B]  series 40[/B]
[I]Lowest ratio[/I]: [B] 13.37:1[/B]
[I]Highest ratio[/I]: [B] 5.5:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 290.93 Nm | 214.58 ft lbf[/B]
[I]Min Wheel Torque[/I]: [B] 119.68 Nm | 88.27 ft lbf[/B]
[I]Acceleration[/I]: [B] 4.81 m/s² | 15.78 ft/s²[/B]
[I]Top Speed[/I]: [B] 50.14 km/h | 31.16 mph[/B]
[/INDENT]
[/FONT]

So: series40 TC 10T sprocket and 55T axle sprocket.

'sid

 

[OzFab]

Use the axle sprocket you have with a TC & you shouldn't have any problems...

200lbs in a AmEx? That's seems a bit much...

 

[scottbahl]

Thanks for the help guys.

I don't know anything about torque converters, let alone how to mount/ implement them. How do I mount the whole torque converter assembly? Do engines have a standard mount for these?

Any info you could give me would help!

 

[landuse]

Thanks for the help guys.

I don't know anything about torque converters, let alone how to mount/ implement them. How do I mount the whole torque converter assembly? Do engines have a standard mount for these?

Any info you could give me would help!

Have a look around the forum to see wha others have done. Search for 40 series TC on the forum to see how they are mounted.

You can also have a look at THIS