Torque converter gearing

[anickode]

Hey all... I'm just curious what is the shortest gear ratio you can get away with on a TAV2 setup is. I've got yet another project on my plate... I've been asked to do a 40mph build on the cheap... I said I'd look into the possibility, but I can't make any promises.

Figure 350 lbs total weight
13" tires
6.5 hp predator

Would a 4:1 sprocket ratio be completely out of the question for a kart driven on mostly flat ground? That would be a 10.4:1 engagement ratio, topping out at 3.6:1, for a governed top speed of 38mph. Would it be a belt shredder? Would it even have the guts to top out?

Discuss please.

First hand experience > theory

 

[itsid]

350 lbs should be fine 370 lbs is already a bit harsh on the belts, but I'd say still within "normal limits"

say ideally 0.1 lower reduction per 20lbs for maximum belt life.
(370lbs 4.1:1, 390lbs 4.2:1, etc...)
With the conservative figures kartcalc puts out, a .2 to .3 difference shouldn't be much of an issue (410lbs max that means)
or if you indeed stick with 4:1 ratio and 350lbs 14" wheels to get a bit more speed (41mph)

but to do so, I'd say original Comet belt no chinese knockoff or it might not last for very long.

So much for the theory.. now let's see if someone has some real world values

'sid

 

[Noseoil]

With a 6.5 hp predator & governor attached (if it's at 3600 rpm) you would need a final drive of 3.84:1 to get you there with a tav (with the 10% overdrive figured in at WOT) & 13" tires.

If you have enough hp... But it might mean a few "tweaks" to the motor, to run well enough to pull like that & maintain the speed. I'm thinking a stage 1 mod would most likely work, not sure the stock motor would get up there without a bit of a run to top speed & it might take a little while to max out the rpms with limited power & gearing like this. Any hills would surely cut down on the pull & be noticed pretty quickly. The 30363 motor would be your best bet to start with for a stock motor. With an air filter, exhaust & jet it would probably be ok.

This is just a guess (large pinch of salt, please) & simply running the numbers on a calculator. The short answer is "I don't know, but I think it should work." The better belt is in order on this type of loading as was mentioned & it might be the weak link in your setup. Worst thing to happen would be having to change final drive ratio to top out with less speed but use the limited hp available, so not really too bad. 40 mph is just a number picked out of the air, so 37 or 41 is still in the ballpark.

 

[bob58o]

See post in other thread. I did't want to post because you said experience over theory and it's all theory and sketchy theory at that. LOL

 

[pRoFiT]

Spend an hour or two and remove governor!!! then even a 6:1 gets you up to 40 with a great low end as well. Then maybe 5:1 ratio would be a nice medium. get the low end and still hit 40+.

Im going to watch this and your other thread. see how it turns out. i run stock pred with 6:1 13" tires and tav2. and get 27mph. want to remove gov but if you get a 4:1 ratio and still have great power....maybe i switch out my ratio

wait maybe i run 15" tires. oh well. about the same.

 

[bob58o]

Spend an hour or two and remove governor!!! then even a 6:1 gets you up to 40 with a great low end as well. Then maybe 5:1 ratio would be a nice medium. get the low end and still hit 40+.

Im going to watch this and your other thread. see how it turns out. i run stock pred with 6:1 13" tires and tav2. and get 27mph. want to remove gov but if you get a 4:1 ratio and still have great power....maybe i switch out my ratio

wait maybe i run 15" tires. oh well. about the same.

Rules stipulate governor mod is allowed, governor removal is not. Unless this is a different build.

Stock engines 220 cc or less. 4 stroke industrial style engines only.
Stock carbs, jetting allowed
Intake and exhaust allowed
Governor adjustment allowed
Governor removal prohibited
Centrifugal clutches only
Must have functional brakes
Must be of quality (ie, safe) workmanship

 

[pRoFiT]

oh okay. so gov mods? if you pull the gov spring off how long until it explodes inside the engine. and would that be an exceptable modification?

Or can you connect throttle to main control valve bypass everything. like override the gov control. i know the insides wont hold together long. but enough to win a race?

So what gov mods can be done\allowed? You see i like to fudge around the rules. always ask a lot of questions find the loopholes. step son of a lawyer makes me this way, i guess??

 

[bob58o]

Adjusting the spring can safely limit RPMs to around 5k, just under valve float.

 

[itsid]

depends on the plastic cast if that'd be considered "safe" or not..
frankly I doubt many governors withstand 5k rpms (or to be precise.. load changes at such rpms)

governor mods allowed... hmmm is removing the weights from the governor allowed?
if so, these have to go,
if not, these have to be fixed to the shaft (glue? C clip? twisting wire?)
that renders the governor ineffective (since it cannot move it can't push the throttle back)

Still 5k rpm load changes.. I don't think it's safe even IF you can remove the weights!

there are two ways to "modify" a working governor
1) change the weights
2) change the spring
it's basically as it is with a cent clutch,
more weight faster engagement,
stronger spring later engagement
or
less weight later engagement
weaker spring faster engagement

strongest possible spring (C clip )
and lowest possible weight (removed the weights)
and it won't work no more.

And while that is safer than bypassing the governor, it's still far from what I'd want to do
on an engine under race conditions...

So: Good luck!

Personally I'd think I'd shave the weights a bit (maybe a third off) and try to adjust the rest to govern the engine at 4500 (4200 is still in the realms of a stock governor)
maybe a bit more ...
the lighter it is, the higher rpms it can takae (inertia is what's killing it) still within limits.
and those depend on the material and cast quality of the plastic gear...
I wouldn't want to place any bets on neither of those, so be prepared.

'sid

 

[anickode]

See post in other thread. I did't want to post because you said experience over theory and it's all theory and sketchy theory at that. LOL

This is a different kart, not for the build-off.

I was basically wanting to know if anyone has successfully pushed a small fun kart at a 4:1 ratio with a TAV2 and not had major mechanical issues.

 

[bob58o]

This is a different kart, not for the build-off.

I was basically wanting to know if anyone has successfully pushed a small fun kart at a 4:1 ratio with a TAV2 and not had major mechanical issues.

Well I'm sorry then.