Python also offers a Staggered Dual system with a hidden cross-over, thus providing some of the benefits of a 2-into-1 exhaust.Įxhaust systems that use a single collector (2-1) are well tuned for low end torque on stock engines, however they can be restrictive at higher rpm’s. All have excellent offerings in straight pipe designs tuned for standard displacement Harley’s. There are drag pipes incorporating 1-3/4 head pipes and 2 mufflers such as those made by Python³, Samson , Vance & Hines, Dyno Power, and Hooker. Remember, bigger isn’t better when it comes to diameter so stick with 1-3/4? head pipes. Removing the baffle will make these pipes real loud but horsepower will suffer. Running long pipes without any baffles fall under the same category as Large/Open Pipes. The washer is then held in suspension in the path of the exhaust, acting as a deflector to adjust the velocity. This requires drilling through the muffler or pipe and welding a washer to the end or a bolt.
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Another remedy is to install a large flat washer toward the end of the pipe body. Installing larger baffles or thunder tubes will change the velocity. The alternative is to install large diameter stepped pipes such as those from Python³ and Samson. While not plagued with the same problems as short drag pipes, a large diameter open pipe will actually restrict flow since the optimal 300 fpm cannot be achieved. Performance will still suffer on the lower end since there is no ability to scavenge gases as with a 2-1 or stock Harley exhaust. When installed inside the head pipes these cones act to repel the pulse waves as they return to the engine and alter velocity as the gas passes through the narrower passage. One trick is to install anti-reversion or torque cones. There are also the longer Drag Pipes which have the look of straight drags but the baffles and extra length help compensate for reversion by providing just the right amount of back pressure. The exception would be the baffled drag pipes offered by Vance & Hines and Hooker similar to the Big Radius pipes and Hooker Troublemakers pictured below. Some drag pipe makers such as Cycle Shack offer special baffles to help tune their drag pipes. Drag pipes are tuned for higher rpm large displacement engines where these pulses can be overcome.
Since the sonic and thermal pulses don’t have as far to travel as in a longer system the wave is able to return faster, thus entering the combustion chamber robbing the engine of power. TIP: Be sure to replace your exhaust port gaskets any time you change or reinstall pipes. So what does all of this mean? To best answer this question let’s look at a few different exhaust designs and how they handle the above listed conditions. Bigger is not always better and a larger pipe will actually slow this velocity thus restricting flow. For the most part all stock Harley engines require a 1-3/4? diameter pipe to maintain 300 fpm. The optimal velocity is 300 feet per minute. This is the rate at which gas travels through the exhaust system. The thermal pulse also reverses direction at the end of the pipe but unfortunately travels at a different rate, thus reaching the combustion chamber at a different time. Similar to sonic pulse, this is a wave created by the hot gas exiting the exhaust valve.
Torque cones can sometimes reduce this condition. Under the right (or wrong) conditions this wave will even push some of the air/fuel mixture back through the intake valve into the intake, a common occurrence with short drag pipes. The wave will also pull exhaust gas back along its path and if it reaches the open exhaust valve the gases will dilute the air/fuel mixture in the combustion chamber. This pulse travels through the exhaust and at the end of the pipe actually turns around and heads back toward the exhaust valve. Sonic pulse, thermal pulse, and exhaust gas velocity.
Without getting into a lesson in physics there are three factors that effect the performance and tuning of an exhaust system. For anyone interested in what will improve performance or why those drag pipes made your ride a slug please read on. If you answered yes to #3 then you’re probably going to put whatever looks cool on your bike and not worry about how it runs.
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