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Making my own baffles for 22 F3S Cat delete
I installed the Cat delete pipe without the plug (db killer) that came with it and the stock muffler and found the exhaust sound very loud and rappy, especially if you wicked the throttle or went to WOT. Before installing the plug to compare sound levels I measured it without the center plug and found it to have approximately 1/2" pipe opening vs the ID of the pipe itself, which is approximately 1.875". This IMO was way too restrictive and would have a lot of increased back pressure at WOT or 7000 RPM, but it may be fairly quiet since it is so restrictive to flow.
After doing some reading including threads on this site, muffler and header manufacturers etc. and contacting bigcitythunder to inquire about their screen type baffles etc. I decided to try and build my own. It appears that there are 2 parts to the sound of the combustion event: the sonic wave travelling at 1100'/sec and the slower sound of the combustion gases exiting the engine. I decided to try and dampen or reduce the db of the sonic wave and at the same time trying not to increase back pressure by choking the flow of the exhaust gases which help to scavenge the exhaust system.
I chose a piece of plate that is 1/8" thick and has a nice pattern of 1/8" holes punched in it. (A little too heavy for this application because it is difficult to bend and mig weld). If you could find a similar configuration of plate but 1/16" thick it would be easier to work with and plenty strong.) The concept (idea) was first drawn out on cereal pkt cardboard so that I could use it to copy the plan to the metal for cutting etc. The volume of 1/8" holes that are in each baffle are just over the calculated volume of the open pipe. The volume of plate used was just over 36 square inches and made two pieces that I could shape into 2 separate baffles. See the photo of the cardboard cutout which looks like a crown. I used a thin circular cutter on a handheld Milwaukee to cut out the pattern.
Once I had the pattern, I had to bend and shape the flat piece into a circle to fit into the ID of the pipe. (I used a large angle iron as the base and beat the 1" pipe over the metal to bend it into a circle. A bit of trimming and a tack weld to hold the circular shape. The four petals were bent towards the middle where they were held together and tack welded to close the 4 seams. Looks like a May mushroom (see photo) and it's not pretty but it appears to be functional.
I installed the first baffle in the top of the pipe pointing down (away from the engine) and the second one is installed by the muffler clamp pointing back towards the first one. Each is held in place with a self-tapping screw for now after drilling the hole the pipe with a bit.
The final result is two baffles that breakup the sonic wave by dispersing it through the holes and changing the internal diameter of the pipe once at each baffle from 1.875" (by 1/8" per side) to 1.625" diameter through each baffle with no straight through path for the sonic wave. This change in pipe diameter is said to be beneficial to reducing the sonic wave through cancellation as well.
Cost of the plate was $15 for a square foot, I still have 70% of it and some MIG welding wire.
The result of these baffles is that the exhaust does not bark, rap, or fart when you wick the throttle. The sound is less than the open pipe with stock muffler but not nearly as quiet as the stock muffler and cat. I am not sure if this will be my final solution until next spring when I can ride again and do some WOT pulls. This is FYI only and not something I recommend you do. I do not believe that back pressure is required to make torque on a 4-stroke engine and there is technical info that supports this on the header and muffler sites. I ran the open exhaust on a two-hour run and did not notice any slowing of the bike below 3000 RPM, as some have reported, but it runs, pulls and sounds great from idle to 7000 RPM. I did not notice any change from the stock to the open pipe system in idle or engine management since the 02 sensor is in the pipe above where the cat delete pipe joins the engine down pipe. Sorry the picture is inverted.
