torque converter gear ratio question

[bobox911]

Hi, I'm new here. I have a question about a gear ratio issue I'm having.
So, I'm building a go kart with a 5.5 hp motor off of a pressure washer and I was planning on using a torque converter with a 10 tooth sprocket. I have a 37 tooth sprocket on the axle, with 13 inch tires. I ran the numbers, and I'm coming up with a 3.7 gear ratio. Would this be a problem, or do I need to get a bigger sprocket? Thanks in advance!

 

[Denny]

Yes, I believe that ratio may be a problem. A 6:1 would be perfect and safe. It’s also what most karts came with stock. 60 tooth axle sprocket with a 10 tooth drive sprocket.

 

[BrownStainRacing]

Hi, I'm new here. I have a question about a gear ratio issue I'm having.
So, I'm building a go kart with a 5.5 hp motor off of a pressure washer and I was planning on using a torque converter with a 10 tooth sprocket. I have a 37 tooth sprocket on the axle, with 13 inch tires. I ran the numbers, and I'm coming up with a 3.7 gear ratio. Would this be a problem, or do I need to get a bigger sprocket? Thanks in advance!

Yea, that gear could be a problem.

If your t/c has a 5/8" jackshaft, you can experiment with a 9t and 8t sprockets, that always helps.

What kinda engine is the 5.5hp ???

Some pump, and washer engines has a different style crank and won't work for a mini bike or go kart.

 

[JimD]

The crankshaft has to be drilled and tapped and have a 3/16" keyway the full length of the crankshaft. The crankshaft HAS TO BE AT LEAST 2.297" long which is the standard go kart crankshaft length. If the engine has a taper to it don't bother wasting your time with the engine, you got free off a power washer so retire it. Denny's suggestion about a 60 tooth rear sprocket is correct.

 

[bobox911]

What kinda engine is the 5.5hp ???

Some pump, and washer engines has a different style crank and won't work for a mini bike or go kart.

It's off of a ryobi pressure washer (similar to HFs 173cc vertical shaft motor) that i have modified to run as a horizontal shaft motor. It has a 7/8" shaft that i have made an adapter up to 1" so i can use it with a t/c.

The crankshaft has to be drilled and tapped and have a 3/16" keyway the full length of the crankshaft. The crankshaft HAS TO BE AT LEAST 2.297" long which is the standard go kart crankshaft length. If the engine has a taper to it don't bother wasting your time with the engine, you got free off a power washer so retire it. Denny's suggestion about a 60 tooth rear sprocket is correct.

I have made an adapter from 7/8" up to 1" and it is 3" long.
The problem I'm having with the axle sprocket is that I'm using an axle out of a 50cc chinese kids atv, so I'm having trouble finding parts for it. I need to check the bolt pattern, but I think the biggest sprocket i can get will be a 48 tooth.
I think the 48 tooth axle sprocket coupled with a 9 tooth on the t/c will get me closer to where i want to be (around a 5 is what i'm shooting for)

 

[JimD]

Should have gone down in size rather than up. The bolt hole pattern around the crankshaft is important for matching up the plate on the TAV 30. How about a couple of pictures of the engine showing the crankshaft and bolt pattern around the engine. Also, a picture of the axle you are work with showing the 37 tooth sprocket and how it is mounted so people could give suggestions on ways to attach the larger sprocket. Also, what chain size are you planning on using? Don't really care what the chain size is for the 37 tooth sprocket because all we are going to do with that sprocket is mount the new sprocket to one side or the other on that sprocket. The critical thing is matching the bore of the sprocket to the new one so it will be perfectly centered.

 

[Rat]

Hi, I'm new here. I have a question about a gear ratio issue I'm having.
So, I'm building a go kart with a 5.5 hp motor off of a pressure washer and I was planning on using a torque converter with a 10 tooth sprocket. I have a 37 tooth sprocket on the axle, with 13 inch tires. I ran the numbers, and I'm coming up with a 3.7 gear ratio. Would this be a problem, or do I need to get a bigger sprocket? Thanks in advance!

3.7 is definitely going to strain the belt even with 13" tires. Add to that your 5.5 isn't going to have as much bottom end grunt to get you rolling like an 8 would so you have to gear even taller to compensate. If a 60t won't be a ground clearance issue, get one. If it will be a problem you can drop the output to a 9t and pair that with a 56t which will place you at 6.22:1 which is what I have driving 2.50-18 motorcycle tires.
I've got enough bottom end grunt that I can easily launch a wheelstand which is why I am about to re configure my final drive ratio.

I'm not going to tell you it isn't possible because I've done it with 5hp push mower flatheads, but converting a vertical to horizontal IS a bad idea generally speaking unless you have one with universal enough mechanical dimensions to part swap a few things, or a pressurized oil system (generally 500cc or larger riding mower verti engines)

This seems to be a cobbled together mismatched build, which by itself isn't an issue but you're going to hit a whole lot of headaches... the ****show hasn't even begun for you yet.

 

[bobox911]

3.7 is definitely going to strain the belt even with 13" tires. Add to that your 5.5 isn't going to have as much bottom end grunt to get you rolling like an 8 would so you have to gear even taller to compensate.

thank you for explaining why it might be a problem.

If a 60t won't be a ground clearance issue, get one. If it will be a problem you can drop the output to a 9t and pair that with a 56t which will place you at 6.22:1 which is what I have driving 2.50-18 motorcycle tires.

the biggest i can go is 48t (frame in the way and hub bolt pattern) I was thinking possibly pair the 48t axle sprocket with a 9t or 8t on the T/C

I'm not going to tell you it isn't possible because I've done it with 5hp push mower flatheads, but converting a vertical to horizontal IS a bad idea generally speaking unless you have one with universal enough mechanical dimensions to part swap a few things, or a pressurized oil system (generally 500cc or larger riding mower verti engines)

i have a friend thats done a few conversions and they've helped me with this one

This seems to be a cobbled together mismatched build, which by itself isn't an issue but you're going to hit a whole lot of headaches... the ****show hasn't even begun for you yet.

this project is my first "from scratch" build (i've done a bit of lawnmower modifying) and I have learned a lot from this build, things to do different on the next one.
I was ridiculously underprepared in both materials and budget on this build, so most of the stuff on this project i got for free or had lying around (hence the kids atv axle and the vertical shaft motor)

attached are pictures of the kart in question (front and back) with a picture of the drivetrain situation (mocked up for now, still waiting on crank and t/c driver)

 

[Rat]

A 9/48 could work... I've heard nothing but a lot of bad about 8t having a tendency to explode but idk personally.

Some final drive ratios to consider based on commonly available sizes, I'd recommend the top two based on availible clearance and the fact your kart is a lot smaller than I was expecting which leaves quite a bit of room for weight penalty but your engine is in the simplest terms, is unproven performance as of yet

9/48= 5.33:1
9/42=4.66:1
9/40=4.44:1
9/38=4.22:1
9/36=4.0:1

Charlotte is a pretty good clip away from me, but you said mower mods.
I've got a Craftsman that needs to go bye-bye.

The 27hp Kohler twin I yanked is pretty much scrap unless someone wanted to replace a few over priced things and all the electrical.
The chassis is fine, and pretty damn big.
It has a mean rear transaxle like I've never seen before... has its own fan, some sort of neutral lockout lever on the rear plate, and it's a 5 lug with massive (but dry rotted and bald) tires.

 

[bobox911]

A 9/48 could work... I've heard nothing but a lot of bad about 8t having a tendency to explode but idk personally.

oh! I haven't heard that before, but good to know for future projects.

Some final drive ratios to consider based on commonly available sizes, I'd recommend the top two based on availible clearance and the fact your kart is a lot smaller than I was expecting which leaves quite a bit of room for weight penalty but your engine is in the simplest terms, is unproven performance as of yet

9/48= 5.33:1
9/42=4.66:1
9/40=4.44:1
9/38=4.22:1
9/36=4.0:1

thanks! i was shooting for between a 5 or 6:1 ratio, so 9/48 should be perfect.

Charlotte is a pretty good clip away from me, but you said mower mods.
I've got a Craftsman that needs to go bye-bye.
The 27hp Kohler twin I yanked is pretty much scrap unless someone wanted to replace a few over priced things and all the electrical.
The chassis is fine, and pretty damn big.
It has a mean rear transaxle like I've never seen before... has its own fan, some sort of neutral lockout lever on the rear plate, and it's a 5 lug with massive (but dry rotted and bald) tires.

do you have a picture of it? sounds interesting... how much would you want for it?
those transaxles are pretty good, did a mower a while back with one of those in it. swapped it out for a 5 speed though.

 

[Rat]

do you have a picture of it? sounds interesting... how much would you want for it?
those transaxles are pretty good, did a mower a while back with one of those in it. swapped it out for a 5 speed though.

Nah, I can get you some. I'll message you so not to muddy up the thread with it

 

[bobox911]

Nah, I can get you some. I'll message you so not to muddy up the thread with it

ok thanks!

 

[Rat]

ok thanks!