05/10/2022
This is a rant about drag/unbaffled pipes but I'll take the long way round to get my point over. Any of you that have had engines built by me will know the process. The first step is usually for me to ask you a series of questions - what are your riding habits, where (RPM) do you change gear, what will the bike be used for such as motorway cruising, short high RPM fun, loaded up touring etc and I always ask which exhaust system you're running. This last one is because everybody underestimates the importance of the exhaust system and the influence it has on the outcome. It's not just a couple of pipes that allow gas to escape from the engine and make a noise. The exhaust has a major influence on how much torque and horsepower the engine can develop and more importantly where in the RPM range these both peak. The exhaust can make or break a build and is as important if not more important as the cam choice. A well designed engine is a carefully chosen collection of parts that all complement each other in order to achieve exactly what the customer wants from his/her build. You can have the perfect injector size for the throttle body and displacement, the perfect exhaust to intake flow ratio through the heads and the perfect cam choice for the available compression but if the exhaust doesn't allow for the required gas speed and density changes as the RPM increases then you've wasted your money. The worst thing you can do to a street ridden bike is to fit an unbaffled system or drag pipes as they are more commonly known. The term 'drag pipes' came about from using open pipes on drag bikes/cars which are designed to run at wide open throttle over short distances - the opposite of what we all do on the road. We usually ride between about 2500 - 4500 RPM which is where torque has to be higher than horsepower so this area is where a street exhaust has to function. Drag pipes are completely useless in this area as this graph by Daren at Sheffer Performance shows us. This is incredible - the red lines are the torque and HP readings as the bike was delivered to Daren with a pair of unbaffled pipes. The blue lines are the same readings but with baffles fitted. Look at the torque numbers at around 2450 RPM ... there's about 75 ft/lbs of torque difference! The whole area between about 2000 and 4700 RPM is a disaster. This bike would be awful to ride on the street. You can see that the only area where the unbaffled pipes produce better numbers than with the baffles installed is from 4700 RPM onwards. If you're a drag racer than this will work. If not, it's a lesson in how to destroy performance in one easy step - remove your baffles.
