Your BMW HP4 probably came with an exhaust system already on it. So why would you change it? There’s a bunch of good reasons to replace the stock exhaust:
Make it faster: The HP4 is actually pretty fast, however manufacturers had to meet a budget. That means that they might have been unable to product the best motorcycle exhaust pipes for your bike.
Make it lighter: Replacing, for example a big, steel system with an aftermarket titanium unit with a single short muffler can yield 15 pounds of more of weight. That can be 5% of the total motorcycle weight. Dropping the weight can be as good as increasing horsepower.
Save money: Usually OEM exhaust systems costs a lot more than aftermarket exhausts. So you’ll have your OEM exhaust secured while you ride with your aftermarket one.
Make it scream: You can change your bike sound, like from a sewing machine to afire-breathing monster.
Your engine can be thought of as a pump, moving a precisely metered mixture of air and fuel into itself, and moving burned air and fuel (exhaust) out. Improving that pumping efficiency is the most affordable way to pick up a few extra ponies. An exhaust that flows better will reduce the work the engine must perform when it expels exhaust gases, especially when coupled with improvements to the flow of air and fuel on the intake side.
Some states have different requirements, our recommendation is to get an answer from your local police department, inspection station, state department or motorcycle shops.
Well, that depends on a few things. Nearly every aftermarket exhaust is louder than the factory exhaust. Some of the performance gain depends on not needing to silence the bike. If the exhaust is too loud, some manufacturers offer quieter baffles that you may install to bring the volume of the bike closer to stock.
Most of the exhausts often have a removable baffle in the tip of the muffler (commonly referred to as a dB killer) that can be removed or installed for similar manipulation of sound levels.
Performance is usually unaffected by the presence or lack of these baffles.
Well, it depends. How good a “wrench” are you? What kind of system are you installing?
The answers vary greatly. We’ve put bolt-on exhausts on a bike and gone riding on it in under 20 minutes.
Consider your mechanical aptitude and understanding of the exhaust system and the related systems requiring disassembly to access the exhaust. Take stock of your tools on hand, and your ability to follow directions.
If any of these seem like obstacles, don’t be afraid to go to the mechanic and have a professional job done. Sometimes, an install from a competent shop for a fair price can give you peace of mind, while relieving you of any possible problems from an exhaust job that was tougher to tackle than originally estimated.
Staying legal can be tricky. Ultimately, it’s up to each rider to follow the laws of the countries, states, and municipalities we live in, ride through, and visit. C.A.R.B. is the California Air Resources Board, and while not all riders fall under its jurisdiction, the laws it promulgates frequently have far-reaching effects for nearly all North American riders.