Exhaust Tinkering Part 2 of 2

left over welds from
perforated screen

At the end of part 1 of 'Exhaust Tinkering' I thought I was going to run the spiral flow muffler, but I couldn't come up with a way of mounting that muffler securely so I pulled it off. I think I need to weld a tab to aid in mounting, but ultimately didn't like how it looked.

I picked up this 2.5" Resonated Exhaust tip by DC Sports a little bit after posting Part 1 because I liked the look of a short muffler on my cb750 Brat build.

Unfortunately, it was way too loud when I installed it and went for a ride around the neighborhood. I tried to weld on some perforated sheet metal over the outlet but it really didn't do a darn thing. 

Sure, it was slightly less loud compared to having nothing on the end of the exhaust header. Even with the baffle insert tucked in the header, it was just embarrassing to see my neighbors come out to see who was on that obnoxious motorcycle coming down the street and the children making faces while putting their fingers in their ears.

I figured I would look at some baffle designs for some of the automotive performance mufflers on the web and then let my subconscious stew on it for a while.

With the cold weather setting in, my mind always goes to projects for the bike. I had purchased a piece of 1.75" exhaust tube from Autozone a few months ago and already had some sheet steel laying around for this time of year. My idea was to cobble together a baffle that I can insert into the resonated exhaust tip and weld it in place. 

resonated exhaust tip

The intention is to prevent the exhaust from getting a clear shot out of the exhaust without some forced change of direction to the exhaust flow.  Every change of direction the exhaust takes is a chance for the sound waves to cancel each other out or get absorbed by the packing in the resonated portion of the canister which I expect to be very similar to a glasspack muffler.

Yes, there will be back pressure introduced with this additional baffle.

DIY Baffle inserted

Did I mention that I'm not a welder? I'm using a cheap flux core harbor freight welder that I bought for the heck of it many years ago.

Deflector welded in place

The base of the baffle was cut from some sheet steel with an angle grinder for the course cut and a grinding wheel to fine tune the shape.

The first hobby tool I ever bought that was not needed for home repair is the Dremel and over the years I always managed to find a use for it even if it didn't see heavy duty use. 

I used the Dremel with a cut off wheel to cut the hole in the sheet steel to insert the 1.75" exhaust tube.

A smaller scrap of sheet steel was bent to form a deflector and trimmed to fit into the exhaust tip. 4 cuts on the edge of the deflector to allow it to sit on the tube to make welding a little easier.

Test fitting the baffle

I intended it to sit a little deeper, but thought it might be easier to seal
with a surface mount due to the excess weld splatter from the old perf screen attempt
even if I can't hide the weld splatter as nicely.

I guess from the results here, you can tell that I'm not a grinder either.

You can't really see the terrible welds when you just look at the bike while standing up. They are not noticeable until you get down and get closer to see the details (even after 2nd grinding session with my Dremel instead of the angle grinder).  After painting the end of the can, I re-installed the modified exhaust but couldn't get the bike started.  The lithium battery died so now I have to track down where the short is coming from.  I'm also noticing that the throttle tube is not snapping back so there are a few things I need to look at that might have been installed incorrectly with my last handlebar swap a few weeks ago. I was planning on starting an oil cooler upgrade but might need to wait a bit longer.

I tracked down the no start to lack of fuel. Apparently my fuel level was low enough to need reserve to get fuel into the carbs, once I figured that out she eventually came to life. 

For the parasitic voltage draw, I removed the negative battery cable and put a voltmeter set to 20 Milliamps between the loose cable and the battery negative and found a 5 milliamp reading somewhere (I didn't know roughly 50 milliamps was supposed to be acceptable until later).  Disconnected fuses and connections to try and track down where the parasitic draw was and ultimately traced it back to a fused relay feeding constant 12V to the dyna ignition circuit and the new speedo.  After removing the tank, I traced it back to the constant 12v circuit for the digital speedo and so nothing to fix.

After getting the bike started, I could tell immediately that the sound level is significantly reduced. The bike seems to rev pretty good and has no trouble idling, but I can't help and wonder if I've contributed too much back pressure to the system but the baffle design is inline with quiet baffle inserts available to purchase in the real world for big bucks (and likely would not fit this can).

After posting my images for comments on Reddit and Imgur, the only comments I got back were the ugly pigeon poop welds. Oh Well.