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Concening "dyno" results, we really don't put much stock in that kind of information for street bikes for the several reasons.
First and foremost, the results you get with a dynamometer are great if you're dialing in an engine for drag strip use—remember, on the strip it's full rpm all the way! Based on that assumption, drag pipes should show the best gain in horsepower over 4,000 rpm. However, put a set of drags on a street bike and you can feel the bottom end and mid range go soggy. When was the last time you shifted your street bike at 5,250 rpm on a regular basis?
We set up our motors/performance work/exhaust systems by road testing in the real world. In other words, we ride them! Based on our testing (and a bit of experience) we can tell when a combination approaches/reaches optimum TORQUE, not horsepower. A lot of riders tend to forget that it’s torque, not horsepower, that you FEEL when you drop the hammer. Without getting into a lengthy dissertation, let me tell you what we have discovered over the years about exhaust systems.... NOTHING beats a good balanced 2-into-one system like those available from SuperTrapp, or the Vance & Hines Pro Pipe. The Thunder Header is pretty good, too, but it’s not our first choice. After that, any staggered dual system which has tunable baffles and equal length pipes will give good results. And forget about anything larger than 1 3/4" pipes on anything smaller than a 100" motor. You want to make power, not lose it. With regards to dyno testing, you shouldn't test a SuperTrapp exhaust system at 6,000 rpm—it's not designed to perform well up there.
...which brings us back to the ever popular drag pipes. We love the sound of open pipes, too, but not the results. If you insist on using drags on the street, select nothing larger than 1 3/4" tubes, and throw in a set of Tork Cones to strike a balance between and performance. Simply put, pipes are like cams. Some give great bottom end and midrange performance, others work best at mid to high revs, and the “top end” cams are a waste unless you’re turning the high rpms characteristic of a race bike. The same rules applies exhaust systems. One pipe can't do every job. Pick the pipe appropriate to your engine parameters and riding style, and you'll be ridin’ happy. |
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