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Drag Pipes

by PocoCJ

Drag pipes are "cool", at least in the minds of some of us. They are the simplest of exhaust systems and so appeal to the minimalist in us. But if you think using drag pipes will give you increased horsepower, you've got another think coming. If, after knowing the pipes aren't the best for performance, you still want to use them, there is something you can do to get better low and mid range torque (power). Even after making these mods, engine power will still not be as good as an engine using a good 2 into 1 or 2 into 2 exhaust system, but it will be a more tractable ride than running straight drag pipes.

Since most folks first think of installing drag pipes to get that LOUD sound and then think of performance, they're often disappointed when they ride their newly equipped bike. Yeah, it sounds sweet once you get the idle jet properly sized, and are standing alongside blipping the throttle, and watching the flames shoot out the end of the pipes. But simply installing drag pipes and rejetting the carb won't make for a tractable ride. Someone new to riding often thinks that reducing back pressure in the exhaust will result in more power. ain't so! Several reputable shops have dyno'd bikes with correctly jetted carbs and drag pipes and saw a significant power loss.

Since most of us operate our engines in the low-to-mid RPM range we seldom use the drag pipes in the region where they operate most efficiently - flat-out wide open throttle! Yep, they'll make more HP up there than other pipes. Doesn't do you any good driving around town or heading to a rally in Timbuktu, several states away. I'm not going into the physics of all this; it will suffice to say that typical street and road riders need lots of torque down low. Drag pipes don't do this without some modifications, and as noted, even then won't match a good header system.

If you still want to run drag pipes (hey, they are the cheapest pipes you can get!), here's something that'll help. It won't make them perfect, but at least livable. To make this tunable mini-baffle scrounge a 1/4-20 x 1" thumb screw, or use a 3/4" OD washer welded to the top of a 1/4-20 x 1" screw. Next drill a slightly larger than 1/4" hole around an inch from the end of your drag pipes. Place a nut and lock washer on your new mini-baffle and slide the whole thing into the hole in your pipe, with the nut, lock washer, and thumbscrew flat or washer inside the pipe. Add another lock washer and nut to the outside, cinch it all down with the flat parallel with the length of the pipe. Of course, repeat for the other pipe!

Now comes the tuning part of all this. Start your bike, let it warm up, and then go for a ride. As you ride, notice any flat spots as you accelerate. When you notice a flat spot, and you will, stop and shut the bike down. As soon as it cools enough to mess with the mini-baffle, loosen the outside nuts, rotate the baffles to about a 15 degree angle, cinch 'em down, and repeat your test ride. Try angles of 30, 45, 60, 75, and 90 degrees. Use the ol' seat-of-the-pants method to decide what works best. If you have the bucks and access to a dynamometer, let it tell you where to leave the mini-baffles. But remember, you're looking for torque, not horsepower.

I've seen this method used in drag pipes since the middle '70s. I stumbled upon it by accident, trying to stick something in my pipes to keep cop nightsticks from going up the pipes and getting a ticket for "no baffles." I had tried the baffles made for drag pipes but they made my Sporty sound like frog farts. So I pulled them out and left the bolt in the pipe. I noticed the flat spot that had been there at about 3000 RPM was almost gone. I told an old HD mech about it; he laughed and said to try using thumbscrews and varying the angle, too. I didn't have any thumbscrews, but had a friend weld a washer into the slot of a 1/4-20 fillister head screw. Worked pretty good!

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