Technical > Automotive > Building motorcycle exhaust...

Building motorcycle exhaust...

I'm not sure you understand how complex exhaust systems are and the high-end physics that goes into them. Commercially made aftermarket products (the good ones, anyway) are very carefully engineered and undergo extensive testing.

Also, I'm not clear on the purpose of putting that much effort into a seven year old bike that, honestly, wasn't anything special to begin with.

But since that wasn't your question, here's my take:

The tools you have are a start; you will also need a welder to attach the gasket flanges and hanging brackets. You don't mention what type of pipe you will be using, but make sure it's something that will take high temperature paint and/or chrome depending on how you want it finished. Chroming is a chemical process that cannot be done by the average hobbyist. Most bike or auto custom shops can do it for you or know someone who can. Expect to spend a few hundred bucks.

How do you plan on measuring backpressure, and do you know what the backpressure tolerances for your Yamaha are? Too much backpressure and the engine will overheat. Too little and you will lose power, especially at the high end. Either way you can mess up your gas mileage and make the engine run poorly or even damage it. Lastly, adding a jet kit changes all your calculations.

I hope this gives you something to think about. If you do manage to pull this off, please document everything you did and take pictures because many 'cycle magazines would pay you well for the article!

Good luck!

mocycler

reply to The Limit
I agree with the first reply.

Part of the reason aftermarket exhaust kits are so expensive is because of the R&D that goes into them. You simply won't come close, and you won't be able to do as good of a job.

Most companies use a process called Mandrel Bending, which essentially, results in a pipe that stays a constant and smooth diameter all the way through. If you bend the pipe like a regular Joe you won't ever achieve the same.

As for backpressure - You want more on the low end and less on the high end. Unfortunatly, the pipe can only be made for one diameter, and you aren't driving a Ferrari which has two seperate intake and exhaust paths for the low and high end of the band. Once again, this is where all the R&D is spent and you have to find a happy medium so you aren't sacrificing too much torque down low for some top end horsepower.
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THIS IS SPENCER. MISSION ACCOMPLISHED - I HAVE JOE. RETURNING TO BASE.

reply to mocycler
What are you guys talking about? You see cheap, almost homemade straight pipes on every other HD on the road. They seem to work very well.......at being loud and reducing low RPM power to point of being useless.
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"If you don't go when you want to go, when you do go, you'll find you've gone." ~ Burt Munro

reply to mocycler
The purpose is to learn something, and I realize the complications that I'm up against.

I realize that the exhaust systems put out there now are expensive for this reason. I'm not looking to make something "cheap" or "homemade". I know the parts with be relatively cheap to purchase.

I realize that this is an uphill battle, but I don't care. If I can make my own exhaust, then by golly I'll do it right, the first time. I have a welder, and I know someone who has a lot of experience using a welder, and does well with one.

This bike might be seven years old, but it only has 4300 miles on it. I bought it with 1100 miles on it 7 months ago, yes I've put that many miles on it, through the winter (20-30 degrees Fahrenheit) until present. So far, I probably have about 3k into the bike, that's including the purchase price which was $2800. The other $200 is replacing fuel/air filter, oil change, replace o-rings, another motorcycle battery, and cleaning the carbs. Other than that, this bike will last me for a LONG while.

I might get something more powerful down the road as the budget permits, but as of right now, I like what I have and I don't ever intend to sell it or get rid of it. This is MY project bike. The bike has NEVER been down except once, and that was my fault, and I dropped it on gravel going less than 3 mph, no scuffs except for a small chip on the left rearview mirror and a few MINOR scratches on the turn signals that you can't even see unless you are within a foot of the turn signal. The battery had to be changed, and that was also my fault (left the cycle on by accident).

Cleaning the carbs out was my fault also, I didn't realize the float bowl had to be drained if you didn't ride the bike for 3+ weeks. The ONLY thing wrong with the bike was the fact that the air filter wasn't the correct one, and we changed it out, 20-30$ fix.

To me, this bike is something special. The fact that the bike sat for so long baffles me. The tires still have a good amount of tread left on them surprisingly, which leads me to believe that the bike hasn't been ridden at all hardly.

I understand that you are trying to be realistic about this, and I applaud you for that endeavor, but I'm not changing my mind on this. I want to do this myself, with help of course, because for me to understand how something works, I have to get my hands dirty. This is the way for me to understand, and to have fun at the same time.

Anywho, enough of the spiel, where would I find the backpressure tolerances? Would this be located in the manual by chance? One thing that I failed to purchase was a manual (buddy of mine has one at school, because he has the same bike).
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Do or do not, there is no try! - Yoda

reply to The Limit

reply to The Limit
If it still has the original tires on it, then spend your money on some fresh rubber.

Keeping the shiny side up is more important than kludging an exhaust.
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The talented hawk speaks French.

That's good advice, and something I was thinking about doing.
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Do or do not, there is no try! - Yoda