gearing a drag kart

[chevyman01]

Im building a go kart with a harbor freight 11 HP engine and plan to up the HP, but im having a hard time deciding on a clutch belt or torque converter if I do a clutch what is a good gear if I want good take off and great top speed, if I plan on running an 1/8 mile will a torque converter be good enough for a Tim around 8-10 sec, I need to know asap,

 

[Joe-405]

its really hard to get 8-10 seconds out of a kart with a fully blown shifter engine much less what your trying. My shifter kart with a 125cc dirtbike engine and 6 gears might run that maybe and its got 5 times the power. I am gonna run mine eventually just for the fun of it but i now its slower than that. I been in drag racing forever and its just something i wanna do once.


Look at this thread (remember this is with a full 6 speed and quadruple your power !!!!)

http://eknclassic.com/viewtopic.php?p=282063&sid=2eeae43b809978fb7095392e15023b8e

 

[Felineman]

If you want to make a drag kart I would suggest going Electric.

 

[itsid]

Well, it'll be extremely hard to reach that even with a TC..

I did some calculations and you need top speed as well as the best acceleration you can get.
let's assume a slightly modified engine (6000 rpm) and a series 40 TC (40 driver)

1/8th mile in an ideal world...
1:7 ratio : 13.5 secs
1:6 ratio : 12.5 secs
1:5.5 ratio : 11.8 secs
1:5 ratio : 11.5 secs
1:4.5 ratio : 11.4 secs
1:4 ratio : 13.3 secs

So your sweet spot will be somewhere around a 1:5 - 1:4.5 ratio..
and that's for ideal numbers, no windresistance or rolling resistance is calculated, so the kart will effectively be slower than that.

and it still doesn't crack the 10sec limit..

maybe you can play with the numbers yourself to see if an odd ratio will at least ideally match your needs but I doubt it.
*shrugs*

'sid

 

[chevyman01]

Ok Thx, and itsid is that 11 sec time with a centrifugal clutch, would a torque converter be better?

 

[chevyman01]

And what can I do to increase my HP on my engine with in a reasonable budget

 

[OzFab]

Let it breathe; replace the air filter & muffler with hi-flow items; you may need to rejet the carb...

 

[itsid]

I did some calculations and you need top speed as well as the best acceleration you can get.
let's assume a slightly modified engine (6000 rpm) and a series 40 TC (40 driver)
...

Ok Thx, and itsid is that 11 sec time with a centrifugal clutch, would a torque converter be better?

No that's with Torque Converter already..
a series 40 with a 40 Driver the 44 will do you no good (less top speed at the same ratio)

I think what you'd need is a 7k+ revving engine which is, let's be honest, quite a task to accomplish
And remember the numbers above are pure math, no parasitic drag is calculate, not even the exact torque values of the engine, just assumed a continuous acceleration to top speed
(you won't have that that in the real world)
So I think you can add 2-3seconds to each of those numbers easily if you want to have the best guess for your final kart.


'sid

 

[chevyman01]

Ok, so with that torque converter do I need a jackshaft? And how do u remove a governor

 

[Jimmy_B]

I ran junior dragsters for years with my son and everybody uses a torque converter. We ran much better numbers than listed above, but we made a ton of power (considerably more than 11hp), we ran large diameter drag slicks and tached the motor above 8k to do it.

A stock 5hp B&S with the governor removed and using a torque converter netted 12-13 sec 1/8 times for us. About 350# of weight w/o driver.