Quote:
Originally Posted by redyaris
My VT500 at 5000rpm, in 6th gear, at around 75mph gets, aprox 87 mpg.
For the CBR600 to get over 100mpg it will need to spin at 3000rpm - 3400rpm at 75mph.
The question is will the CBR600 engine be happy at this low an rpm under these conditions?
My GS 500 did not like going below 3500rpm...
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Erratic running at low rpm is caused by air flow reversion. It is caused by too much overlap and aggravated by too low velocity in the runners.
So, low rpm operation can be improved through less overlap (free) but might require cam regrind towards less duration (can prove expensive).
Smaller carbs can help in this matter (check Suzuki Inazuma 750 vs GSX-F 750)
Also, I might be wrong but a much bigger load through very tall gearing means your carbs are more open to sustain the speed despite less rpm hence more velocity.
Finally, I believe a guy called motoman partially filled his head inlet tracks with epoxy to improve mid range torque.