Motorcycle Safety & Driveability: Drag pipes for VTX 1800, vtx 1800, power waves

Question
I bought 2" Cobra Drad Pipes for my 02 VTX 1800 and feel like I lost power in the high-mid to top end.  I have modified the air box for more air and have a K&N filter.  What can I do to get power back.  I'm thinking a Power Commander?


Answer
Scott,

Thanks for the question.

Essentially, you've gone and changed the airflow through the engine so much that the stock fuel injection maps can't cope with it. A power commander will most likely be the best solution.

You did not specify how you modified the airbox- was it just a K&N filter, or something more? Your airbox modication may be the reason you have lost power in the upper revs. In modern motor system design by big companies like Honda, enormous research is done on how to develop useable power from engines while meeting strict exhaust noise and emissions limits. One way to boost power is to use the airbox as a "resonance box". Power waves (basically, sound waves) move through the engine, exhaust, and airbox while the engine is running, and they can be "tuned" to push more air through the engine at certain speeds. When you change exhaust systems (altering backpressure) or modify the airbox (changing the resonance), a power loss is usually the result. Just stuffing more air into the engine and changing the injection maps doesn't always cure it. The three parts (engine, exhaust and airbox) are designed to work as a system, and it's easy to throw it out of whack when you make changes.

A lot of cruiser riders find that once they add louder pipes, the bike sounds better (and/or looks better) but runs poorly. This is true of most any engine system, especially modern ones.

The most likely "cure" for the powerloss will be to add some backpressure back into the exhaust, either by using a different system or by adding in some baffles (if possible). The airbox needs to be returned to stock form, but I would continue to use the K&N filter because it flows a bit more air but not too much more. If you are not willing to "quiet" the exhaust system a bit, you may be stuck with the power loss. The Power Commander may go a long way to solving the problem, but only if the airbox is returned to stock form.

Good luck!

Bill Roberson