Gearing / High Speed Help

[TBNRGoKart]

So I recently had watched CarsandCameras Build the 88 mph American Express 2.0, and I got to thinking, I wanted to build something similar, but so far I have frame design, but in the video they used #35 chain, 12t cent clutch sprocket and 38t axle sprocket on 11" tires (I think thats the correct info), so I looked into it, I want to try and hit about the same speeds, 60-70mph, and so far I've come up with either 18t/54t 3:1 Gearing, 13'' Tires at 103 mph, or 12t/38t 3.17:1 Gearing, 13'' Tires at 97 mph, of course I know that this doesn't factor driver / kart weight, and I'm about 5'9 and 140 lbs, would this get me to those speeds / what gearing would be best / what chain would be best, I read some other places on the forums that #40/41 chain is good for offroading and high stress stuff, and if you don't buy the cheap #35 it would work fine, but which one would be best? The chassis is going to be similar to an American Express 2.0 chassis, exept using 1'' Square tubing, Any opinion helps, Thanks! (The engine I would use is a upgraded Predator 212)

 

[JTSpeedDemon]

First thing we need to know is:
What's the powerplant??
A stock or mildly modded engine will not get you to those speeds without costing you a clutch a mile.
The C&C 2.0 had 20 HP, so it could get away with it, so unless you're planning to spend ~$1000 on powerplant stuff alone, you will absolutely not reach those speeds.
Also, C&C never hit 88 mph with the 2.0, more like about 75. Even with the 5 speed lifan, they never breached 80.
Simple reason:
Aerodynamics.
Your kart is gonna need an absurd amount of power or super-slippery aero to reach those speeds.
Also:
Where will you drive it that fast?
And even then, it's incredibly dangerous, and the steering will be very sketchy if you're not careful with designing the front end.

My 2c.

 

[TBNRGoKart]

I was going to try and mod the engine, new flywheel, billet arms, new valves, bronze guides, new valve springs, new cam, remove the govenor, and a 24mm carb, I was also thinking if i can get one for the right price a 2 stroke 250cc dirtbike engine, because I know those things have decent top speed, but the thing I need help with the most is the gearing, but yeah, probs like a stage 3 kit for the 212 maybe?

 

[JTSpeedDemon]

I was going to try and mod the engine, new flywheel, billet arms, new valves, bronze guides, new valve springs, new cam, remove the govenor, and a 24mm carb, I was also thinking if i can get one for the right price a 2 stroke 250cc dirtbike engine, because I know those things have decent top speed, but the thing I need help with the most is the gearing, but yeah, probs like a stage 3 kit for the 212 maybe?

That won't work.
The 2.0 had a stage 4 212 and it wasn't enough.
And either way, it would be an absolute necessity to put a billet connecting rod it there to keep your engine from being a ticking time bomb.
There's a possibility that a 2 stroke dirt bike engine would work, but it's still kinda iffy.

 

[TBNRGoKart]

Ah, ok, In the video they said it was like a stage 3 / 3 1/2, what gearing would i need though to hit about 45-50 mph with a 212 stage 1 or 2 and 13" slicks?

 

[BigWes]

I can make a piece of junk go 45 mph with an unmodified engine...just saying...stage 1 will go a little faster but mainly better Accel and bottom end pull

 

[Kaptain Krunch]

250 2 stroke bike engine will do it, make sure you have 4 wheel disc brakes and good steering.

 

[KartFab]

A) 12/36 = 46 mph at 3600 rpm, 70 mph at 5500 rpm
B) 12/48 = 35 mph at 3600 rpm, 53 mph at 5500 rpm
C) 12/60 = 28 mph at 3600 rpm, 43 mph at 5500 rpm
D) 12/72 = 23 mph at 3600 rpm, 35 mph at 5500 rpm

options a and b will burn up your clutch
option c will let you run on flat ground and very small hills
option d is really the only all around best option, and 35 mph is hauling butt on a go kart or mini bike. It really is going very fast at this point.

People dont realize they spend 90% of their time below 20 mph on a go kart. and if you spend all that time spinning your clutch,then it will heat up and ruin it.

If you want to go for speed only, who knows how many runs you will get out of it. You cant get a high speed geared go kart to play nice when you just want to drive the kart around, unless your idea of playing nice is jittery engagement, detensioned clutch springs, and metal annealing.

 

[TBNRGoKart]

Thanks, so if i remove the govenor, get a billet rod, and 26lb vavle springs, i can get it up to about 5500rpm, and 12/72 is the best for #35 chain?

 

[JTSpeedDemon]

I think that 26lb valve springs will let it rev a little higher than 5500 rpm, since that's where the stock springs float, but IDK.

 

[itsid]

you need
~12 HP to reach 60mph
~17 HP to reach 70mph
~25 HP to reach 80mph
~35 HP to reach 90mph and
~48 HP to reach 100mph

for a yard kart top speed on a flat level road (no further acceleration possible)
just a little less for a race kart with fairings.

and the faster you go the less important the weight gets it's AIR DRAG you need to fight!

And while you can squeez 12 and maybe 15 horses out a predator 212...
I doubt you'd get close to 25 much less 48

And it has nothing to do with gearing and or rpms of your engine
without power gearing high or having excessive rpms are pointless!

reaching 90mph
thrown from a tall enough cliff.. certainly..
driving downhill... maybe..
on a level road .. NOPE I call BS on a 90mph predator 212!

well you can make a 17horse predator thrown several hundred dollars at it
then add nitrous oxide and you'll get there.. but the engine will be toast afterwards
and you need to start over again.
A Motorcycle engine is cheaper to get and can do the same thing way more reliable.
(a super kart engine can do that [and lots more] out of the box if you're willing to spend the money)

'sid

 

[BigWes]

I'm not sure I'd want to try 90 on a yard kart frame. Sounds like a bad idea. My experience so far with yard karts is with mine at least is they all get kinda sketchy at, around, and above say 45 mph or in the general speed range...

How is everyone else's experience in this area?

 

[Joe-405]

A 125cc 2 stroke will get you there also quite easily. I had one.

 

[Hellion]

I'm not sure I'd want to try 90 on a yard kart frame. Sounds like a bad idea.

Well he said he was building a custom frame based on the Am Ex 2.0 and with square tubing (as if that was the gold standard).

To fabricate a kart that goes in excess of 55 MPH, I'd want to eliminate all the slop a typical yard kart has in the steering linkage (heim joints), the loose tolerances in the spindles, and upgrade all the bearings and so forth. I'd definitely have speed rated racing tires and not some cheap Chinese dolly tires.

My experience so far with yard karts is with mine at least is they all get kinda sketchy at, around, and above say 45 mph or in the general speed range...
How is everyone else's experience in this area?

They get very twitchy the faster you go, and the margin for error also grows because of the twitchiness. You have to have nerves of steel and muscular finesse.

Blah, blah, blah. Regardless of all that, if you want 103 MPH out of 212 cubic centimeters, go for it!!!

 

[pearl111]

TBNRgokart, WOW if you do achieve your goal please send a video. I would love to see this.

 

[950speed]

If your going to spend big bucks then get a TaG X125T
I think it makes ~30 hp
It’s a two stroke
Spins up to something around 15k rpm and is already built

 

[KartFab]

Thanks, so if i remove the govenor, get a billet rod, and 26lb vavle springs, i can get it up to about 5500rpm, and 12/72 is the best for #35 chain?

12/72 or 12/60 are both good choices. If you have seen my nephews mini bike video he has 5:1 gearing (12/60 for you) on his, and he accelerates really quick since he is a light person.

 

[JTSpeedDemon]

12/72 or 12/60 are both good choices. If you have seen my nephews mini bike video he has 5:1 gearing (12/60 for you) on his, and he accelerates really quick since he is a light person.

With minibikes you can usually get away wiht taller gearing due to the reduced weight.
Another example would be my One Tire Fryer:
It has a 66T sprocket and a 12T clutch, with 13" tires.
Generally, that's too high, but because it's a flathead(more torque), I can get away with it with actually not bad low end.