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406
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10/20/2014
Location
INLAND EMPIRE, CA
US
Fantasy
1623rd
GouldRacing25
4/5/2020 2:15pm
4/5/2020 2:15pm
Edited Date/Time
4/8/2020 6:10pm
Boyesen 04 exhaust flange $85
951-813-8949
951-813-8949
The Shop
Get one of the Boyesen exhaust flanges while you still can. If you don't think it will make a difference, take off the stock one and look at the shape of the exhaust port - the port is D-shaped (laying on its side) and the stock flange is round! This is an uncharacteristic engineering oversight or manufacturing shortcut (at least for Honda) - I'd estimate 30% of the area is mismatched. The Boyesen flange is a work of art and matches the port shape exactly. I, too, looked for a less expensive option. I looked at the Pro Circuit part - it's stronger, but it's still just round - it does NOT match the port like the Boyesen part. I couldn't find it anywhere but Boyesen. Trust me, it's worth it. Combined with one more tooth on the rear sprocket, a RAD valve and a JD kit, the bike is now an absolute beast, and feels nothing like the stock motor. It went from mellow and smooth but strong to a real eye-watering arm-stretcher.
Here is a pic of an 04 cyl. exhaust port. So the flange being sold is only designed for an 04 model as the box sticker indicates above.
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The 04 Boyesen exhaust flange is oval like the oem cyl. to match the exhaust port.
I think Honda used the 03 model round exhaust flange on the 04’s from factory. I was told that Honda was trying to cause a turbulence effect on the 04 exhaust port area by using the round flange. Supposedly that was the reason for the mismatch on the exhaust flange for the 04 model. Don’t know if that is fact or fiction.
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