engine size and sprocket ratio: faster

[Jody400]

hello all, although i have owned go karts since i was in third grade i am new to sprocket ratio and attempts to make a go kart faster. I will explain what i have and what i would like to do:

i have a large yerf dog (that i only paid $100 for by the way and all it needed was a new carb.) it looks identical to this one: http://www.monstermarketplace.com/go-karts-and-mini-bikes/yerf-dog-32001-go-kart

i believe it currently has a 10 sprocket to 62 sprocket but its that type that has the clutch with a belt that goes to the torque converter and then to the drive sprocket.
the tires are currently 18 inches but i found a set of 22 i will eventually put on.
the motor is currently a techusum 6.0 and the go cart only goes maybe 20mph.

i am debating on putting a briggs 9hp on there. what will i need to do in order to get this go kart 35(+)mph. that is the speed of my other 3 go karts.

i am going to assume i need to buy the 9hp and then get a drive sprocket with around 40 teeth. how fast do you think this would go? or should i just use the 6.0 hp and change sprocket, how fast will that go?

i really wanted to make this an electric start but i can get the 9hp at the same price as 6.5 with electric start.

what other ways can i make this go kart faster?

thanks for any assistance...

jody k

 

[the-cyborg]

More horse power does not equal more speed.
industrial 4 stroke engines are factory governed and tuned to operate at about 3600 rpm, doesn't matter if it's 2.5 hp or 25 hp.
More HP= more torque.
RPM+ gear ratio+wheel height+torque= speed
Of course weight of kart+ rider is a major factor also.

That being said how about posting some pictures of your setup, maybe we can help you get geared to achieve your goal.

First things first on a TC a worn belt will severely effect your speed and power. take a look at the gear ratio calc here----> http://www.diygokarts.com/speed-calculator.html just using the figures you have given you should already have a theoretical speed of around 31 mph @ 6.2:1 gear ratio.

 

[Jody400]

continue

i do understand that hp is not everything with speed of a go kart. are you saying that with a identical setup a 6hp engine will run the same speed as a 9hp or even a 15hp engine?

the belt is new but i am not sure it is the correct belt. i looked up the info on this go kart and it is suppose to go up to 34 mph. why do you feel it is only going about 20mph? i can live with 34mph.

 

[Jody400]

continue with pics

here are some pics of the setup...

 

[Russ2251]

Hmm... A re-run.

 

[jrmints1415]

What i think you have is a torque converter with a 6.2:1 gear ratio. when you have a tc you can get away with higher ratios. A higher hp engine will not increase speed it alows you to get to your top speed faster.

I think you can get away with a 50 tooth rear sprocket and get moving pretty good...

 

[Doc Sprocket]

Jody, we'll do our best to help you out, but please do not start multiple threads to ask the same question. I have merged your threads and removed the duplications. Thank you.

To address your questions-

You're really pushing the limits with the small engine and big tires. You can get away with taller gearing when you have a CVT, but it's not a miracle pill. While it is true that horsepower does not equal speed, that statement comes with a disclaimer: If you do not have the horsepower to attain the speed, you just won't attain that speed.

In other words, your current top speed is pretty low, because it has to be. Gear higher, and you won't gain much more top speed- if any at all- because you're short for power. Put those 20's on, and you're really up the creek.

If speed is important to you, your best bet is to install smaller tires, and gear up. Otherwise, you have two options-

1) Go get a "big-block" engine, 11hp or more. Your CVT will not work with the larger engine, you'll have to but a Comet 40 or equivalent. To make the new engine physically fit, you'll have to modify the engine mounting plate. You'll have to purchase and install or fabricate a jackshaft, as the new CVT does not come with one. Then you can re-gear.

2)Bike, quad, or sled engine. A whole other fabrication challenge.

Also-

A higher hp engine will not increase speed it alows you to get to your top speed faster.

Not entirely true. If you are overgeared and underpowered, swapping engines will allow a higher top speed.

 

[Jody400]

Appreciate

Appreciate the help
The re post was an accident, did not think the first went through cause internet acted up. Was goin to delete but have not been home to do so.

I may go with a 6.5 cause
I can get it with electric start and i want to put headlights on. Not to mention it would be nice to turn a key and not pull. I need a new engine for my other go cart anyways
Does anyone know where the cheapest place to get a slightly smaller sprocket would be?
Will prob also go a size smaller on tires.

Is there an aftermarket starter and alternator, strator, for a go kart engine that was not originally made with one?

Thanks again.

 

[r_chez_08]

I have 1:6 with a 6.5hp clone 19" tyres and a 40 series tc. It is great on flats but uphill it struggles.

 

[Doc Sprocket]

I have seen aftermarket electric start kits for the Hondas and clones, I don't know if they exist for the Tec you have. Check EvilBay.

 

[Jody400]

I guess what i need now is peoples opinions:
B.S. 9hp for $250
Or
Lifan 6.5 with electric start and to run headlights for $200.

I keep going back and forth on this
If the 9 and 6.5 perform the same then i would rather have lights and electric start

Thanks

 

[Doc Sprocket]

What is the shaft size on the 9hp? See my above notes regarding shaft size. If that's not a problem, go with it. To he// with electric start- go with a more powerful and reliable engine.

 

[kendelrk]

i agree with toystory, a new engine isint going to take 5000 pulls to start, probablly 1-3 and thats not going to take much out of you. didnt B&S make a 9hp vanguard with a 3/4 shaft and mounting plate of a 5hp?

 

[Doc Sprocket]

Speaking from experience- A properly tuned and maintained engine (of good quality) will easily and consistently start in 1-2 pulls, even when quite cold. I have taken my kart out in the winter at 20*F and colder, and had it start from a dry carb in 1 or 2 pulls, never more. Honda. Snowblower? One shot- 2-stroke briggs. Lawnmower? 1 pull- 2-stroke Lawn-Boy. Chainsaw? One yank- 2 stroke Mac. Weedie? 2 tugs- Homie. You get the picture. On the other hand, my kids kart has a 4hp clone, low hours, properly set up and maintained. Starts when it feels like it, which means sometimes one, sometimes 2 or 3, and on occasion, more.

What I'm getting at here, is that dollar for dollar, the Briggs is a better bet. You get a quality powerplant with more power. With everything as it should be, it's a very easy pull start, you won't miss the electric. As far as lighting is concerned, go get a 12v, 7Ah gel cell and mount it. Rig a light on a switch, and just charge the battry periodically. Been there, done that, not a big deal.

 

[kendelrk]

well my briggs is still needing help and i surely cant figure out why. 5hp tecumseh 2 stroke? 1 pull. neighbors old Jacobson blower with a rebuild carb? 1 pull. briggs lawnmower? 1 pull. homelite clone? 1 pull. a good motor thats been taken care of or brand new will start easy, and a briggs is alot better parts wise than a clone.

 

[Jody400]

Thanks

The 9hp b and s comes with the 3/4 inch shaft. Most hp i can find with tht size.

The electric start isnt the main reason, it was more for the headlights. I had put some thought into running just a battery and charging as needed. Will prob just go with this.

Thanks

 

[Doc Sprocket]

I ran a battery and light combo for quite some time. As long as you keep an eye on the power demand of the lighting, it's really no big deal. To put it into perspective, a standard driving light is 35w, which at 12v works out to be about 1.5 amps. A 7.5AH battery like I used, will supply 7.5A for 60 minutes. Therefore, the battery will supply a 1.5A load for 5 hours, or 300 minutes. Now, while all these numbers are "ideal", there's still a very respectable run time between charges. If you run LED lighting, the battery will go bloody forever between charges.

It's great that you found a 9hp engine with a 3/4" shaft- go with it!

 

[Jody400]

Another question:
The current motor has a shaft that is almost 3 inches long. The 9hp motor that i am looking to buy has a shaft that is 2 27/64 long. Is this difference in sizes going to matter. It is equipped with the comet clutch, see picture above.

Lastly, where can i find what size belt the go kart is suppose to have. It seems like the current belt is too big.

Thanks

 

[jrmints1415]

Not entirely true. If you are overgeared and underpowered, swapping engines will allow a higher top speed.

are you sure because i thought the only thing that could increase speed was higher rpm's. If they both spin about 3600 rpm dosnt that make them go at the same speed thus making this a question of gear ratios that higher hp engines can handle?? I know its not reall discussed anymore but im just kinda curious

 

[Doc Sprocket]

An engine with higher horsepower (and torque) has the pulling power to allow a higher gear ratio. Therefor, even at the same 3600RPM, a higher top speed. And yes, I'm sure.