Biknut Prototype SBP Exhaust

I wasn't planning to install a new exhaust today. In fact I was planning to go on my first really long ride on the Cadillac. I would of been gone all day. Before heading out, I decided I'd give it a wash job. Washing your bike is a good way to check it all over to see if anything is going wrong.

Almost right away I noticed the muffler was breaking apart at a weld between the header and the muffler. About 12 hours later I was testing riding this.



I bought this SBP Ex chamber last year. I never installed it because it looked too difficult, and I was happy with the stock modified pipe I had. In the last few weeks I've held it up to the Cadillac a couple of times, and decided it wouldn't fit very well, and put it back in the box.

The Cadillac has a really narrow BB spindle. Holding the pipe in the perfect position under the BB, the little muffler on the end of the chamber wouldn't fit between the crank, and the tire. Aiming out the right side, it had to be too low in order to clear the right side chain, and sprocket.

I got the idea to use the stock header, because of the way it broke off. After figuring out I couldn't go under the BB, I looked at going high on either side. I didn't like that, so that just leaves the back of the bike.

The one metal I can weld is copper, so most of my pipe is copper. All I did was decide where to mount the muffler, and then extend the header to it. Placing the muffler outlet low, and back by the rear axle has appeal from a noise standpoint. I'm guessing a longer header isn't better for performance, but it is what it is.

This is my first report after 1 test ride,

I was very surprised by how quite it sounds. WOW. To bad the motor makes so much noise. There's a spot around 6500 rpm where it sounds like someone dropped a fork in the garbage disposal omg.

I could feel a noticeable improvement in the bottom end and mid range. The top end which was pretty darn good before, is still good, maybe a little better. Part of the way was uphill, and it was accelerating nicely when I let off the throttle at about 36 or 38. It's always felt like it will do about 40 but I'm afraid it will blow up doing it. Now it'll just blow of faster.

The actual feel of the bike seemed a little different riding. The center of gravity may be a little lower. The weight of the muffler isn't supported by the engine now either, so I'm hoping the exhaust will become more dependable now. The muffler is mounted in 2 places.

Next I'll paint the whole thing BBQ black.


This exhaust was as much about just seeing what's possible as making an exhaust.

Probably if it turns out to be dependable. Now that I understand how to mount one a little better, I could see myself buying one that's shaped different.

I'm thinking the concept of having the muffler hang it's weight from straps is better than the stock set up.

I rode around quite a bit yesterday testing the new exhaust. It does work great, but I'm not satisfied with my rear muffler mount. The steel strap, and conduit clamp I'm using is too flimsey, and not going to cut it. I noticed the muffler body tries to twist toward the frame slightly. I need something else to attach the muffler body to the frame, that's a little more solid.

I'm going to toss the conduit clamp, and metal strap, and try something else. I have 2 hose clamps big enough to fit around the muffler at the fattest part. I'm looking at the 2 threaded holes where the rear caliper used to go for a good solid mounting point.

Help me figure out what I can use to attach the muffler, to the caliper mounting holes. I'm thinking a metal tube or rod, hose clamped the muffler.



This is better. What you're looking at here is a much stronger rear muffler mount made from a 5/16" steel rod, hammered flat on one end, and drilled to bolt to the two, rear caliper mounting points. The rod is bent in a kind of C shape, or L if you will. The lower end of my bracket, which is just the 5/16 rod bent to fit, contacts the top of the muffler and is held in place by two large hose clamps. This mount is very sturdy. This is battleship.

How does the SBP Expansion work? The answer is very well thank you. With a 24" header pipe my bike has great bottom end and mid range. It starts better than before too. Top end is about the same, or a little better than my modified stock exhaust. Top end was never an issue, it's the bottom end and hill climbing mid range that I wanted to improve. Exhaust noise is also very low. The engine makes more noise than the exhaust now.

No tuning was needed after installing the SBP pipe. It was running a little rich before installing the pipe, and it's still a little rich.

Another big improvement I'd like to point of is in the area of vibration. I've read on the forum about people saying running the stock exhaust without a lower bracket, causes more vibration. I've never run a lower bracket on my stock mufflers, because I don't care for the looks of it. I've assumed the high end vibration was normal and nothing you could do about it, but not anymore. Having the muffler mounted solidly to the frame, and using 2 rubber connectors SBP includes with their kit isolates the weight of the exhaust from the engine, and engine vibration. I notice a big difference in smoothness at high speeds now.

Because of this, I have to give this SBP expansion chamber 2 thumbs up.