Need help with speed and gear ratio

[ryansclzo]

Hello,

This is my first go kart and I got this frame off someone for $100.

I am going to buy an engine for it soon and also want to buy a sprocket at the same time.

Let's assume I buy this engine:

http://gokartsusa.com/Honda-Gokart-Engine-Minibike-65-3.aspx

I am confused about gear ratios. When I use the speed calculator, and use a 6:1 gear ratio, the top speed is only 20mph.

I have a couple questions:

How can I increase top speed without hurting the clutch?

Does horsepower or other specs matter when picking out an engine?


Thanks for all the help!

 

[Half-breeder]

If getting a 6.5 clone... I suggest a "Predator" engine... cheaper, and if there's a "Harbor Freight" nearby, you can 'just' go grab one for 80-120$... just FYI.

On the 'safe' side... a 6:1 ratio is recommended to save a Cent Clutch... however, if the total weight (rider included) is less than 300-350lbs, and running 10"-11"wheels... IMO a 5:1 is 'do-able'. Not sure... but looks like a 10" wheel in rear... so a 5:1 on 10"s = 20-21mph w/ stock engine. Which is pretty zippy to say none the less... this is what mine looked like driving w/ same wheel and gearing... back in the day...
https://www.youtube.com/watch?v=ys_-qd89Ip8



Increasing topspeed, w/out hurting the clutch, is plausible, either by decreasing the gearing/ratio, increasing engine RPM's or HP. Seeing as that a 5:1 is possibly the borderline for clutch longevity (w/ 6.5hp), to increase topspeed a 'variable' gearing is suggested... known to us as a TC/CVT (Torque Converter/Continuously Variable Transmission) Youtube is full of info bout them. Clutch slippage and low RPM's are the 2 contributing factors that kill CClutches. Most all stock engines of the caliber we are talking, have a governor that hinders RPM's to exceed ~3600. Removal of governor will increase RPM's to ~5000, which increases topspeed even w/ same gearing. Anything past that $$$ comes into play aswell as shortened engine lifespan. HP does play a key roll in several aspects. The more hp the less chances of a CClutch slipping, which 'can' mean a 'safer' decrease in ratio to go faster, because said hp/engine is able to 'overpower' the drag of the wheels/ratio.

If 'speed' is what you're after... and you need an example of possibilities...? I run a Honda GX200 ('clone' originator) moddified to 10-11hp, using a TC w/ a ratio of 4.5:1 on 16" wheels and can travel alil over +50mph... what that looks like and its abilities...

https://www.youtube.com/watch?v=oUOm6yL5fys


This probably confused you more than it informed you... I apologize if that be the case.

 

[landuse]

Good info there Tihm

 

[ryansclzo]

This probably confused you more than it informed you... I apologize if that be the case.

Thank you for the detailed response! I definitely want my kart to go at least 30-40mph.

What's the best way to make that happen?

 

[Half-breeder]

Thank you for the detailed response! I definitely want my kart to go at least 30-40mph.

What's the best way to make that happen?

How deep are your pockets?

A HF212 6.5 'clone' w/ governor removed=5kRPM... 100$ plus a gasket for cover.
A TAV2 TC geared to 4:1 will get you to 40mph at 5kRPM w/ those wheels, plus wont have to worry bout low rpm clutch burns or a neccesity for HP upgrade(s), plus youll have the main building block for futuristic upgrades, like lager wheels, for more initial torque... 150$

 

[ryansclzo]

How deep are your pockets?

A HF212 6.5 'clone' w/ governor removed=5kRPM... 100$ plus a gasket for cover.
A TAV2 TC geared to 4:1 will get you to 40mph at 5kRPM w/ those wheels, plus wont have to worry bout low rpm clutch burns or a neccesity for HP upgrade(s), plus youll have the main building block for futuristic upgrades, like lager wheels, for more initial torque... 150$

Okay thanks. So the engine is around $120, and i'm wondering what tav2 means?

Would this one work http://www.amazon.com/TORQUE-CONVERTER-CLUTCH-COMET-218353A/dp/B00FQQ2CXG#customerReviews

Also are there any cheaper torque converters? And what kind of gasket would I need


Thank you

 

[Half-breeder]

Okay thanks. So the engine is around $120, and i'm wondering what tav2 means?

TAV2 is the 'name' given to a 30 series TC 'kit'. In addition (as far as I know) a TAV2 is the 'only' 3/4" shaft (engine drive shaft) TC that is setup to have an 'over-drive' (whatever mathematical sum you come up w/, for topspeed... add 10% to it). This vid has the calculations and formula of equations needed to figure out torque and speed using the TAV2... I ended up copying it n watching it atleast 20 times... supplying my own #'s... that exercise of equations gave me an idea of what kinda performance to expect... but like the description says under my nic... "Slanted" looker @ things... I mentally see things, that other's cant/dont/wont/coulda/woulda/shoulda seen.

TC/CVT Calculations...

Would this one work http://www.amazon.com/TORQUE-CONVERTER-CLUTCH-COMET-218353A/dp/B00FQQ2CXG#customerReviews

Yes, 'that' is actually a really good price for a China knock-off of a 'name-brand' TC... same as the one I run. 'That' one is setup to use a #35 chain... however not the correct tooth count to attain the 4:1 ratio... you would need a 15T, which 'can' be purchased separately (looks like you have a 60T on your axle)... or you could use the 12T that comes w/ the TC and get a 48T for the axle. Either way the ratio = 4:1.

Also are there any cheaper torque converters? And what kind of gasket would I need?

Like I said... 'that's' a really good price for one... and the only other 'cheaper' ones, Ive seen, are used/2nd hand.

The name of the type gasket is called a 'sump cover' gasket... usually 2-3$.

...and pls just for kicks n giggles... fill out your profile, as best as possible. TY

 

[ryansclzo]

that's[/I]' a really good price for one... and the only other 'cheaper' ones, Ive seen, are used/2nd hand.

...and pls just for kicks n giggles... fill out your profile, as best as possible. TY

I really appreciate the help. So I should go ahead and purchase that TC, and then get the appropriate sprocket for the engine 4:1 ratio.

All these adjustments will make the engine safe from dying? With the governor out and having a 4:1 ratio how much would that shorten this engines life?

FYI I filled out some things into the profile

 

[Johnnyboy]

Well, removing the governor can be dangerous. If you plan on bypassing it I would recommend a billet flywheel and rod. They can be expensive, though.

 

[Blazkowiez]

Grab a 10 tooth clutch and see how it runs, you'll be doing more than 20mph with a predator and the ratio you've currently got on that kart.

 

[Half-breeder]

All these adjustments will make the engine safe from dying? With the governor out and having a 4:1 ratio how much would that shorten this engines life?

If you only remove the governor the stock springs flutter at +/-5k RPM which is fine. The more RPMs the shorter the life span of the engine... but removing the governor has been done 100s upon 1000's of times to even more engines than not. If you keep the oil changed frequently w/ proper viscosity, you should have no issues w/ longevity. The 4:1 ratio wont shorten the life span of the engine, parsay, but 'worse case' is ya may eat a belt at times... asfar as normal wear is concerned.

Well, removing the governor can be dangerous. If you plan on bypassing it I would recommend a billet flywheel and rod. They can be expensive, though.

NO NO NO... NEVER EVER 'bypass' a governor... NO NO NO!!! The gear INSIDE of the case that controls regulation of RPMS 'can/may' break apart, due to high RPMs(4k+). REMOVAL of the governor is the ONLY 'safe' method of attaining higher RPM's.

... and billit conrods are 'recommended' for rpms that are HIGHER than 5k...

Grab a 10 tooth clutch and see how it runs, you'll be doing more than 20mph with a predator and the ratio you've currently got on that kart.

... ummmm ...

... I definitely want my kart to go at least 30-40mph.

What's the best way to make that happen?

 

[Johnnyboy]

You are correct, "bypassing" was not the correct term. "Removing" is the appropriate word.

 

[Blazkowiez]

In response to half-breeder, nothing you've said is wrong from what I can say.

I'll just state that typically when we've tached any of these motors stock, wot is 3900-4100 its not 3600. Yes 3600 is the max rpm these should be running but these engines don't get everything correct.

Thats why I was saying you'll be doing a bit more than 20-21 even with the ratio given when you do the math.

Given its been maybe 3 years since I've had to turn a wrench on a kart maybe what I remember has changed since then.

 

[Half-breeder]

In response to half-breeder, nothing you've said is wrong from what I can say.

I'll just state that typically when we've tached any of these motors stock, wot is 3900-4100 its not 3600. Yes 3600 is the max rpm these should be running but these engines don't get everything correct.

Thats why I was saying you'll be doing a bit more than 20-21 even with the ratio given when you do the math.

Given its been maybe 3 years since I've had to turn a wrench on a kart maybe what I remember has changed since then.

I understand, however not everyone has a tach and if you wanna get into "details" the atmosphere, air pressure, weight, tread type, ply rating, traction, grade/slope level, fuel octane, oil level, how large a poop one 'just' dropped.. and the list goes on and on and on... are all things that can determine a karts performance/speed difference, from what calculations indicate... but why confuse him?!?!? Figuring you 'should' know by now, we only deal w/ specifics... when brought up by the OP... and on a 'norm' for the technically specific questions itsid 'keys in', and Ill fade out (due to I try not to insert inferior info, and if I do, it's usually by accident, due to lack of sleep, and my eyes/fingers cross wires, w/ something wife has me doing mentally).

Besides, in post #2 I had stated the #'s... w/ a preceding '~' symbol... I was taught that ~ has a meaning of 'about/round-abouts', which would inadvertently mean that the 3600 # was an estimate according to specs. Seeing as that he stated that he wants to travel at 30-40mph(not abit over 20-21mph), I explained a TC w/ the gearing along w/ the removal of the governor(~5k rpms) would achieve that for those that read it.

10" wheels, ~5000 RPM, 4:1 ratio = 37mph + 10% = 40-41mph... mathematically. Constituting drag/wind resistance weight/HP and a big dinner... guessing topspeed of closer to 38-39mph... which would put him at the speed hes wanting for sure... instead of hoping for one of those 4000 rpm stock factory 'oops' engines.

 

[ryansclzo]

I just picked up the kart from the person I bought it from, and it is pretty small. Looks bigger in the picture. I can fit in it, but I don't think I want to go 40 in it lol.

With 5:1 gear ratio, 11" tires, and governor taken out I should expect around 30mph.

I just went and got the predator engine from harbor freight. The store marketed the exact one half breeder wanted me to get at $250!! I asked for it up front and got the same item number at the online price ($120).

My plan is to take out the governor and then get a centrifugal clutch. Now I have more questions...

How does the keyway work? If I buy this clutch: http://www.ebay.com/itm/US-Go-Kart-...her_Vehicle_Parts&hash=item2ecc8c1ce3&vxp=mtr

Will I need to buy more keyway so the clutch doesn't move side to side?

 

[Half-breeder]

End bolt should sandwich it down to no side to side movement. Just use locktite on the treads to prevent vibrational unscrewing.

... and my kart is the same size as yours (I'm 'fun' sized/lil guy)... and I do 50+mph... just fyi.

 

[ryansclzo]

End bolt should sandwich it down to no side to side movement. Just use locktite on the treads to prevent vibrational unscrewing.

Do these clutches usually come with the end bolt?

Another thread said that the bolt should be 5/16, 24 count.

Also the last step is mounting the engine which I should be able to manage.

Thanks for virtually building my go kart!

 

[Half-breeder]

Normally, don't think so...

... and no good w/ thread size/counts. I just know the threading is different than an actual gx200.

 

[Blazkowiez]

Do these clutches usually come with the end bolt?

Another thread said that the bolt should be 5/16, 24 count.

Also the last step is mounting the engine which I should be able to manage.

Thanks for virtually building my go kart!

I have yet to see any clutch come with a bolt (sold a few thousand, I think I'd remember that bit).

You're right on the threat count, typically we ordered 1 1/4" bolts a thick washer and a lock washer. We never felt the need for any sort of thread locker needed once you use a lock washer.

If you don't have an impact wrench to install the bolt/washer you can always use a longer wrench and something to tap it into place.