In the search for more power from a motorcycle, the first move is usually to change to a louder pipe. Modern fuel injected engines make this easy as the closed loop adaptation from the O2 sensor often has enough range to adapt to the free flowing exhaust to get the mixture right back on the map without any electronic "rejetting". A cutaway of the muffler of the PCX, and other photos I have seen where people have actually disassembled the can to remove it's guts, shows that the gasses come in the front through the catalyst, travel to the rear in a large pipe where they exit into the volume of the can, come back to the front of the can through a few large baffle openings where they enter another smaller pipe that runs all the way to the back again where they run into one more flat "wall" baffle before rushing around it to get out. An excellent, large volume design and almost as silent as any car. I like cheap homebrew mods so I decided to try some Black and Decker tuning and save my $300 from buying a nice Leo Vince. If I didn't like it I can always find a take off exhaust to buy that someone else has just laying around after replacing theirs.
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The cutaway image wasn't completely accurate in showing all the supports inside the can so I ended up with a few extra exploratory holes but eventually found a sweet spot to open up the can which eliminates the trip through the long skinny pipe and the dead wall baffle at the outlet but I get to keep my cat and my $300. That muffler is built to last! The steel is very strong and is 1-2mm thick. It could very well be a structural part of the swing arm.
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The original small pilot holes surprisingly let out very little additional flow or sound so once I found some open room I went to larger holes in two steps. I had two 10mm holes and it still didn't sound very loud while revving on the stand so I drilled one more. Now that I have ridden the bike I would probably recommend a little less as it is getting pretty loud at full throttle but does still settle down to a tollerable level while cruising being just audible above the music in my in ear monitors.
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The dynos of the CBR250R usually show big gains at the lower rpms, dying away to 0% gain through the first induction tuning suck out from 4,500 to 6,000, and gaining again to 9% up through the upper midrange with a big peak at 8,700 and then falling back to stock above that to redline. The drilled PCX feels about the same. A CVT bike will never run at low rpms so there is no performance to gain there and the final pull to top speed at 9,600 rpm feels about the same although cruising at 9,000 rpm is using less throttle than before. Not a big gain at full throttle on top.
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Fuel economy is up slightly by 2-3% as is the weighted hill climb speed, from 48 mph to 49.5 at 7,000 rpm. 0-50 mph test runs were very windy again and are quite difficult to do accurately but averaging all of the two way runs, the improvement was less than I would have thought. Down only .3 seconds from 13 to 12.7.
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Next up will be some DR Pulley sliders at 12gm and then a "1500 rpm" (whatever that is referring to) torque spring to increase the pulling rpm from the stock 6,600 up closer to 8,000.
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