Tractor Racing
In order to achive more speed you need more power. Right? WRONG! Not always, most small engines have more power than you actually need. Your average riding lawnmower usually comes with a single cylinder, flat head, verticle crankshaft, 16 hp engine. Now, you may have a 48" mower deck with 2 spindles/blades. This takes approximatly 2 hp to turn them fast enough to cut grass. You may also have a hydrostatic transaxle, which at top rpms of 3600 at the crank, will reach an average speed of 5 mph. This takes about 5 hp to do on a surface of less than 10 degrees inclination. So, you are using a max total of 6-11 hp. Now what about the rest you ask. ITS UNUSED!! Suppose you wanna race it, with stock pulleys, engine, transaxle and drivetrain, youll never win. Now, in order to increase your ground speed, you must increase your transaxle output speed, in order to do that you must increase transaxle input. Now there are two ways to achieve this, the first would be to make the engine speed(rpm) higher. The second would be to modify your drive vs driven ratio. On almost all mowers, the engine pulley is smaller than the trans pulley simpley to put less load on the engine. Which means if you have a 3" diameter engine pulley and a 6" diameter trans pulley, your engine is turning twice as fast as your trans input, in other words you have a 2:1 ratio. Now, with this kind of ratio you are producing more toque at the drive wheels. Suppose you were to make it a 1:1 ratio, your trans input would be the same speed as your engine output speed, and you would be making full use of all your hp. Now say you wanted to double the ground speed, you would need a 2:1 ratio at the rear. Which means you could put a 3" pulley on your trans, and a 6" pulley on your engine. This would be a lil bit too much stress on a staock engine, because it would not have the acceleration of the 1:1 ratio, thus bringing us to engine performance upgrades. Exhaust and intake are your most important and most noticible power increasers. The less restriction in your exhaust, the better it will flow and sound, cuz an engine that cant breathe is not a good engine. Intake is tricky to do, carb extensions, placing the carb farther from the engine will help, but you also need to think how can I get more air/fuel into the engime, so a larger carb and intake/exhaust ports will help you here, now what to do with the extra air fuel, cylinder bore and increased stroke, because now you can fit more in the engine, and a higher compression ratio(less cylinder volume when compressing the mixture). This should be a great start point and provide a base to understand what you need to do, and to devlope some of your own ideas. Thank you for reading this and please visit my website, http://johnny-rebel0.tripod.com/tractorboyracing
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