Honda Shadow Aero Pipe Modification
Various Drill Bits (working up to desired size)
Drill bit extentsion
3 or 4ft. 1" pipe
Sine I have gotten a bunch of E-Mails asking what I did, I thought I would make a How-To. This modification is to increase the sound and possibly the power of a Honda Shadow with stock exhaust. The stock exhaust on the Aero has a "2 into 1" exhaust. Which if you look more closely it has 2 pipes into one muffler but inside the muffler are 2 pipes that run through it. Here is a diagram of the internals of the stock exhaust:
On the back side you should see two one inch openings. Each of those has 3 baffles inside. One at roughly 6 inches, 1 foot, and one and a half feet inside the muffler. Depending how loud you want it to be is how many holes you should drill and how far. I wanted my loud as I could make it without having to re-jet it. I like the amount that I drilled the pipes because it's loud and sounds good at full throttle, but idle and some throttle it is quieter but it does not have that tinging sound that some bikes have when they drill out the baffles.
What I did
First, I drilled the inside of the exhaust pipes out. I used a small bit with a extension on it and drilled around the inside of the pipe making about 8 holes. I then worked up to the next size until I got to a 1/8 (The largest I had). There was then some metal left hanging and this is where the pipe comes in. I took the pipe that fits perfectly inside the 1" exhaust holes and knocked out the remaining part of the baffle. I repeated this for each of the baffles till I got to the curved part of the exhaust. And then I repeated this for the second of the two exhaust pipes.
I then checked the sound and wasn't bad, but I wanted to go louder. If you are content with the sound you should leave it. As you can see from the diagram, there is one pipe in the middle that helps in muffling and transfering the exhaust. So I drilled small holes at 3 o'clock and 9 o'clock. This creates the straight pipe effect. The exhaust now doesn't have to take a single path. I then simultaneous would drill the holes at 3 o'clock and 9 o'clock bigger and deeper. The deeper you go it seemed like the louder it got. I would use your judgement and drill the amount and size hole for the sound desired.
Some of my observations. Just drilling the pipes not only did not destroy the muffler, but it also did not create any cackling. After drilling out the pipes I increased my gas mileage 2-3 mpg. And there was a noticable performance increase. I drilled out my old Rebel 450 and there was backfiring, but when I did this on the Aero there was basically none. I have over 15,000 miles on my bike and it has backfired about 2 or 3 times, which it might have done anyways.
Thanks again for all your help Keith! I had an opportunity to take my pipes off on Wednesday night and drilled out the baffles. As you had stated.. it was not that difficult to do.I did as you said.. I used a small drill bit all the way around and then used a larger bit to make it easier to hit out. After that I used a pipe to knock them out and then a grinding stone to clean out the rest.After that I drilled out three smaller 3/16" holes through each baffle and had the pleasure of riding it yesterday. It was 44 degrees here in Minnesota yesterday and I brought it out for a short ride and it sounded so much better thanks to you! I now know what you mean about it sounding almost stock at idle and at cruising speed, but when you crack it open.. WOW it sounded great. My son says it sounds more like a chopper now. I was a bit nervous about doing it because I did not want it to sound like my buddies who's sounded tingy and cheap, but I am very happy with the results. It sounds like a much bigger bike and again I thank you so much for all your help.