Air box mod save $$$

[Greg_imp]

In spite of my own numbers, something changed when I modified the exhaust. Throttle response seemed more lively, as I've said elsewhere, I felt less vibration, and of course it sounded much better. The aesthetic experience of riding was enhanced.

Since my ECU / ECM is stock, my bike is limited in rear wheel speed and rpms. My rough calculation is that at 7,500 rpm my motor is sucking in about 140 cubic feet of air per minute, which is in the range of a medium sized shop vac. Obviously, the intake plumbing creates some resistance which results in some reduction of air mass in the air box. Air mass sensing is the biggest factor in EFI, since it has to accommodate quite a large range of atmospheric pressures. Ferret was recently at 14,000 feet and it would be interesting to hear if he noticed any difference in performance given since at that altitude atmospheric pressure is about 15% of what it is at sea level.

My point is that adjusting for air mass is the main thing the ECM does, so small changes in intake resistance are not going to make any difference in performance, at least below 7,500 rpms. However, if the rpm limiters are removed, a much higher air flow is possible and then intake air resistance might be a factor.

I don't know how to explain the feeling of increased liveliness without a measured change in the hp curve, but again, in my experience, this resulted from exhaust changes, not air intake.

I believe CIP57 reported faster speed trials with the stock air intake than with "opened up" intake. I've read in other places that there's some serious mojo put into air box design, what with resonance and all that but that is all way above me.

edit: with ECM limiters in place, peak dyno hp results vary depending on what gear is used. In 5th gear, rear wheel speed limits hp below 80, in 4th gear you might see 80. I got 85 by running in 3rd gear and it appears that rpm limiters are what sets the peak reading. YMMV.

edit: edit: In 1st, 2nd, 3rd rpm limits dyno peak hp. In 4th and 5th the stock rear wheel speed limit caps the peak hp.