Predator 420 with 40 series CVT

[mckutzy]

Leave the gov intact internally/externally as stock if you DON'T want to remove it entirely.. ie. opening the sideplate and removing the gov internals...

Or... remove it entirely... Internally and externally....

Those basically are the options.... or face certain destruction...

And to have it the stock setup is fine...it will be just limited in certain cases...

 

[67StingrayJ]

Leave the gov intact internally/externally as stock if you DON'T want to remove it entirely.. ie. opening the sideplate and removing the gov internals...

Or... remove it entirely... Internally and externally....

Those basically are the options.... or face certain destruction...

And to have it the stock setup is fine...it will be just limited in certain cases...

I removed the governor. Took it apart and got rid of the oil level shut off as well. One mistake I made was when I pulled the counterweight out I didn't put it back a tooth off. So when I sealed up the case again and turned the engine over I got a terrible knocking. The thing spun nice and free with the case open but once it was all perfectly lined up it just barely hit the back of the crank. Lesson learned. So, if you open the thing up, make sure you either mark the location of the counterweight in relation to the rest of the engine, or make sure it doesn't hit when you put it back in.

 

[67StingrayJ]

What is the gear reduction ratio On the 40 series CVT?

 

[LightningTeg]

I dont think there is correct me if Im wrong....

 

[Kartorbust]

Look at the table. 2.43:1 with the 40 and 2.83:1 for the 44.

 

[67StingrayJ]

Thanks Kator.

When I calculate my gear ratio for my buggy, do I take the 40 series CVT into account? Currently I have the 4 series driving mated to a 10 tooth that drives a 31 tooth on the axle. I thought that meant I was running a 3.1:1 ratio but now I'm now so sure. And then there are tires too... 18" tires...

 

[Kartorbust]

Thanks Kator.

When I calculate my gear ratio for my buggy, do I take the 40 series CVT into account? Currently I have the 4 series driving mated to a 10 tooth that drives a 31 tooth on the axle. I thought that meant I was running a 3.1:1 ratio but now I'm now so sure. And then there are tires too... 18" tires...

You include the sprocket from the 40 series with the sprocket on the axle. If its 10 on the 40 series to a 60 on the axle, with the high ratio of the 40 being 1:1, it'll be a 6:1. If you are using a 44, it'll be 7.44:1 because it does not quite have the 1:1, but 1.24:1 so you multiply the gearing by the 1.24:1 which gives you the 7.44:1 for your final drive.

It's a bit confusing but it makes sense once you have all the numbers you need in front of you.

 

[67StingrayJ]

OK, check my math here guys. The lowest ratio I have on the 40 series is 2.43:1. On the driven I have a 10 tooth and 31 tooth on the axle. So that gives me 2.43*3.1=7.533. Is this the best gear ratio I can expect to get?

 

[Kartorbust]

For all intents and purposes, you are swapping an industrial engine for a moped powered kart. You're going to need to swap the axle sprocket for a larger one or run a jackshaft to get your final ratio close to 8 to one to make it perform similarly to the original engine. You can run a 25 tooth to a 10 tooth to the 31 axle and that will give you a ratio of 7.75:1 and should be fine for the final drive. Your low end will be 18.83:1.

 

[67StingrayJ]

ok, simple question here. With a 10 tooth on the 40 Series and a 31 tooth on the axle, I calculate my ratios to be 7.533:1 and 3.1:1. Is this right?

 

[Kartorbust]

Yes those seem to be the correct ratios.

 

[landuse]

ok, simple question here. With a 10 tooth on the 40 Series and a 31 tooth on the axle, I calculate my ratios to be 7.533:1 and 3.1:1. Is this right?

With a 3.1:1 and 18" tyres, it just seems like you are going to run into troubles with being geared too tall

 

[67StingrayJ]

With a 3.1:1 and 18" tyres, it just seems like you are going to run into troubles with being geared too tall

But I have a 7.533:1 ratio. The 3.1:1 ratio is only on the top end, no? Am I mistaken?

I guess what I don't understand is when everyone says you want to shoot for around 6:1 ratio, is that on the top end or on the low end? Won't the 7.533:1 ratio give me enough torque to make it up hills and such while the 3.1:1 ratio will give a bit more speed?

What am I missing here?

 

[Kartorbust]

The part that matters the most is the final drive which is the sprocket on the cvt and the axle.

 

[Dingocat]

What they're saying is the actual sprockets, nothing else. So those need to be the ~8:1

 

[67StingrayJ]

The part that matters the most is the final drive which is the sprocket on the cvt and the axle.

what is my final drive then, 3.1:1 or 7.533:1?

---------- Post added at 11:56 AM ---------- Previous post was at 11:47 AM ----------

I appreciate everyone's help on this. I'm at a crossroads here. I either cut up the frame to make space for a new, larger sprocket or live with my current setup that that as a gear ratio anywhere between 3.1:1 - 7.533:1.

Is my current set up not going to work? isn't a 7.533:1 ratio good enough to go up hills and such?

When people say you need roughly 6:1 ratio, are they ignoring the fact they may have a CVT?

 

[KartFab]

Your target top speed at 3600 rpm WITH a torque converter should be around 40 mph. As a general rule of thumb, most go karts are set up at a 6:1 (sprocket ratio) and you can set up a mini bike for 5:1 (sprocket ratio).

This does not include the drive ratio of the torque converter. If you gear at 3.1:1 your torque converter belt will likely slip a lot until it engages the torque converter. Im not saying its not driveable, just that you will probably end up slipping your belt for most of the low speed stuff.

Ever drive a stick shift vehicle? If you gear like you are now it wil be like trying to start driving in 3rd or 4th gear instead of 1st or second. Lots of slipping and burning before you actually are locked into gear.

 

[67StingrayJ]

Your target top speed at 3600 rpm WITH a torque converter should be around 40 mph. As a general rule of thumb, most go karts are set up at a 6:1 (sprocket ratio) and you can set up a mini bike for 5:1 (sprocket ratio).

This does not include the drive ratio of the torque converter. If you gear at 3.1:1 your torque converter belt will likely slip a lot until it engages the torque converter. Im not saying its not driveable, just that you will probably end up slipping your belt for most of the low speed stuff.

Ever drive a stick shift vehicle? If you gear like you are now it wil be like trying to start driving in 3rd or 4th gear instead of 1st or second. Lots of slipping and burning before you actually are locked into gear.

Yes, I have driven a stick for many years but I can't get past how I initially (and effectively) have a 7.5:1 ratio and how that's not good enough.

 

[Kartorbust]

Your final drive right now is 3.1:1.

 

[landuse]

You have a 3.1:1 sprocket ratio as it sits now. Without moving. It doesn't matter what your "final ratio" is going to be when the kart is moving because if your ratio is terrible to start with (3.1:1) you are never going to get moving enough to reach that final ratio that you are going on about.

Like kartfab says, your belt is going to slip forever and probably never really engage the CVT. Go get into your car, put it in 3rd gear, and try take off. That is what you are trying to do with your kart as it sits now. Will your cars clutch last or work effectively taking off in 3rd gear all the time? Probably not. And that is exactly what your kart is doing at the moment.

You need a general sprocket ratio of 6-7:1. Don't even think of the overdrive that the CVT might give you once you are going. You first have to get going before you can expect to get those benefits.

So what you are going to have to do is change out that 31T sprocket for at least a 54T or a 60T.

Done!