Best Torque Converter For Go Kart
Article by Mark Trotta
A torque converter is a simple automatic transmission that has a low and high gear. They are commonly found on go karts, ATV's, mini-bikes, and snowmobiles. The low gear is ideal for when you're going up hills or driving slowly, and the high gear lets you achieve top speed. They are also a good choice for stop and go riding.
Torque Converters - Advantages
Compared to a centrifugal clutch, torque converters offer better acceleration from a stand still. They also allow karts to be geared for a higher top speed.
Torque Converters - Disadvantages
Unless the engine is idling, a T/C belt is constantly under a slight tension. Although slight, the friction from the belt tension will decrease rear-wheel horsepower slightly. For this reason, centrifugal clutches are preferred over torque converters in most forms of high-speed kart racing. An exception to this would be a small kart track with lots of tight turns and low-speed corners.
To choose the best torque converter, here are five things to consider:
- Off-road or Pavement Driving?
- Engine Horsepower
- Live Axle or Fixed Axle
- Diameter of Crankshaft
Fixed Axle (One Wheel Drive)
Go karts can use a variety of rear axle types. The most common for yard karts is the fixed, or "dead" axle. A single wheel drive runs a chain from the engine clutch straight to the drive wheel, which has a sprocket mounted directly to it. This means that the rear axle does not turn and the rear wheels spin freely.
Since power is applied to one wheel only, the other rear wheel is left to spin, or "free wheel". This allows better steering and cornering. For pavement and hard-packed dirt, single wheel drive with a centrifugal clutch works satisfactory.
Live Axle (Two Wheel Drive)
Off-road karts work best with two wheel drive. In sand or loose dirt, where a single wheel would often spin out, a live axle has both wheels turning at the same time, giving you twice the traction. Having a torque converter is ideal for climbing hills and inclines.
A centrifugal clutch does not work well with a live axle, and under constant use, will burn out. If you plan to use your kart for off-roading, live axle with torque converter is the way to go.
Driver Pulley vs Driven Pulley
On small engine torque converters, the front pulley is called the driver, and the rear pulley is called the driven. The driven pulley can be swapped out to a different size, giving you the option to change gear ratios. By having two or three different pulleys you can best adapt your kart to different riding scenarios.
Chinese vs Comet Converters
The main visual difference, aside from the stickers, is that the Comet converters look smoother and refined, whereas the knock-offs look less finished. Aside from complaints that the knock-offs make a clanking noise and the Comet T/C's are practically silent, I have not heard of anything terrible about the Chinese-made torque converters.
Buying A TC Kit
Buying a complete torque converter kit gives you everything you need; engine mount plate, jack shaft with sprocket, drive and driven clutch pulleys, belt, mounting hardware, and instructions.
The three most common sizes of go kart torque converters are 20 series (light duty), 30 series (medium duty), and 40 series (heavy duty). Check your engines output shaft diameter, and order the kit to match the chain-size/pitch of your kart's axle sprocket.
20-Series Torque Converter
For small engines putting out no more than eight horsepower, a 20-series torque converter can be used. Driven clutches are available in both 6" or 7" diameter, for either 5/8" or 3/4" shaft diameter. A 20 series converter uses a conventional (symmetrical) belt. They are often used for low speed requirements such as lawn tractors and off-road karts.
30 Series Torque Converter
The most common torque converter size is the 30-series. They are available for either 3/4" or 1" engine shaft size, and work best with 3 to 8 horsepower engines. Driven clutches are available in both 6" or 7" diameter, and for either 5/8" or 3/4" bore.
Most 30-series torque converters are asymmetric, which means one side of the pulley is flat. Both the driven's and the driver's movable faces and the spring mechanism are on the outboard side of the belt. Asymmetrical belts are also flat on one side, and have a top width of 3/4". This style is common on many TC kits.
Bullet Lines is one of the most popular and lowest cost 30-series converter kits. Two styles are offered; Model One comes with a #35 Chain and a 12 tooth sprocket. Model Two comes with a #40/41 Chain and a 10 tooth sprocket It is recommended for 2 horsepower to 7 horsepower engines.
Shop: Bullet Lines 30 Series Torque Converter Kit
Another popular 30 series TC kit is the Moosun, which includes both drive and driven clutch pulleys, belt, aluminum engine mount plate, built in jackshaft with sprocket, mounting hardware, and instructions. Includes both 10t for 40/41 chain and 12t for 35 chain
Shop: Moosun 30 Series Torque Converter Kit
The Moosun kit fits all engines with a 1" crankshaft, including Briggs, Honda and clones, Kohler, Lifan, Robin, and Tecumseh motors. The kit comes with a 5/8" driven clutch with 6" inner diameter.
40 Series Torque Converter
If you're running an off-road kart, ATV, or LTV with 10 horsepower or more, you need a 40-series torque converter. These are rated for 8 horsepower minimum and 25 horsepower maximum. The 40-series torque converters have a 1:1 final drive ratio.
Drive clutches are available for 3/4", 1", and 1-1/8" diameters. Driven clutches are available with 5/8", 3/4" and 7/8" diameters. A symmetrical belt is used with the 40-series torque converters and they require the use of a jack shaft.
The Jeremywell 40-series torque converter is a popular and low cost T/C kit. Recommended for 8-18 horsepower engines, engagement range is 1600-3300 rpm. No instructions are included with this kit.
Shop: 40 Series Torque Converter Kit
Comet 340 Series
The Comet 340-series torque converter system is designed for Jr. Dragsters and drag-style go-karts and mini-bikes. These are designed to be faster out of the hole (standing start). Like 20-series converters, the belt and pulleys are symmetrical. The drive clutches on 340-series torque converters ship un-calibrated, so roller kits and spring kits must be ordered separate.
Most karts use either a #35 or #40/41 chain and sprocket pitch/size. An easy way to check to see what size chain you have, is to measure the distance between any two teeth on your axle sprocket.
3/8" is a #35 pitch. 1/2" is #40/41 pitch.
Torque Converter Installation
Aside from basic hand tools, some creative thinking may be needed during installation. This is because torque converter kits are sold as "universal", meaning they may not be an exact fit for your application.
Torque Converter Maintenance
In addition to cleaning, older torque converters may need a new belt, as the rubber will eventually harden and crack from age. They also get slightly narrower through wear, which effects low-end torque and top-end speed. Spraying on a little belt conditioner every now and then will help prevent slippage and glazing.
Crankshaft Sleeve Bushing
A crank diameter can be increased with a shaft adapter bushing, also known as a crankshaft sleeve. These will allow you to keep or swap components such as a torque converter pulley.