A few weeks back, I took off my Coffman shorty pipe and reinstalled the stock exhaust in an attempt to increase my "stealth" factor. A couple of tanks of gas later, I noticed I was getting 1-2 mpg worse. At first I attributed it to the fact that I was running the bike higher in the rev range because it was so much quieter and I wasn't worried about pissing off homeowners living on the routes on which I do my hard riding. Regardless of how I rode, the mpg never was quite was as good as with the Coffman, so I put it back on a few days ago and, sure enough, mpg jumped back up in the 40-41 range.

The only other mod I have done is the clean air/block off plate mod. Anyone have a possible explanation for this?

Oh, side note - I did a few 3rd and 4th gear pulls from 30-70 with both exhausts from a set point and could feel no difference. Additionally, 70 came up at almost the exact same point in the road with either exhaust on. If there is a hp loss with the shorty, it's too small for me to tell!

Other side note - I know it's totally superficial but the exhaust from the short pipe is just so much more visceral. I'm keeping it on and just need to remember to not be a highway hooligan...

 

Maybe....

If the bike is 200kg wet weight (nice round number) and you're adding 1 mpg more with the standard pipe then is this due to extra weight of the pipe (and a slight constriction of airflow)? 200kg/40mpg is around 5kg per mpg, how light is your aftermarket can versus the standard can? (Rider and luggage weight not considered.)

 

Slip-on saves me about 12 lbs (5-6 kg) but since I posted that, mpg has dropped significantly regardless of which pipe is on. I'm now getting approx. 32 - 33 mpg so I'm not sure what is going on. In the next couple of weeks, I hope to replace the fuel pressure regulator, put on new chain and sprockets (520 kit, -1 in front), and check my valves. Hopefully, it'll either help or I notice something obvious when I start pulling parts off!