I've found small engine bikes (50 or 100cc say) decrease speed in corners because of the G loadings - you can hear the engine labour and slow down.
A low powered bike will increase you corner speed because you just have to ride the bike harder - maintain momentum,use the brakes less, keep the corner speeds higher and get on the gas earlier. I've been doing this all my life and find it more fun than a high powered bike. My current bike is an '87 BMW R65 - I could have the exact same bike with an 800 or 1,000cc engine, but the 650 is more fun. The 650 makes 2hp less than the 800cc engine - but I have to work the bike for that 2hp less...rev it higher, plan my corners,get my entry speed higher, keep that speed through the corner and get hard on the gas as soon as I can. Horsepower makes me lazy, I don't like being a lazy rider.
Ever gone to a MotoGP event? It is fascinating to stand in a corner and watch the different classes come through. The smaller bikes are just as fast in the middle of the corner but of course it's a totally different riding style, all about conserving momentum. The big bikes have to brake much harder on entry, and are spinning the rear tire on exit. So, the smaller bikes appear to be much smoother while the big boys are forcing violent transitions.
Power usually being directly proportional to displacement, a smaller engine generates less gyroscopic effect, thereby allowing its rider to manoeuver it more quickly and forcefully. That obviously is not the sole factor but it definitely has an effect.....
I used to have a Honda XR200 (w/XR250 forks and rear shock)
I found that I was faster on the XR200 than I was on a CR250 or YZF450.
I think I could just ride the little 2 valve 200 at 10/10ths all the time. I was managing the throttle much less. I was probably at wide open throttle more than with the more powerful bikes. Flick it around and twist the throttle to the stop. I could actually focus on the riders in front of me. Analyze their riding style. Plan ways around them. On the more powerful bikes, it was all about controlling this monster below me. Keeping it fast and under control. I didn't have time to plan the next corner. Ifelt like I had this 250 2-stroke (or LC 450 4 stroke) trying to kill me.
Your results may vary.
The magazines always talk about crankshaft gyroscopic effect, and how larger engines are more reluctant to turn. Not that the larger engined bikes are slower in corners, just that they take more effort to enter the corner.
While I'm no expert, I'm not sure I agree. I simply can't ride a small bike as effectively as I can a larger one. Maybe it's because of my 210 pound weight, or maybe it's just what I grew up riding.
Certainly, there are many smaller engines with large flywheels and heavy crankshafts and many large engines with very light weight crankshafts.
My old RZ350 was a great example. It had a very heavy, complex crankshaft and flywheel assy. Yet, it dropped into corners with ease. My GPZ750 had a crankshaft that was actually lighter, but was far more reluctant to turn. I think overall weight, tire size and geometry play a bigger role.
I ride big bore dirt bikes. I simply cannot ride a 125 like I can a 500. The weight difference is not that much, yet the big bikes are easier.
The gyro effect of a rotating engine internal mass changes 90° on longitudinal engines like BMW or Honda Goldwing and many others.
I don't accept that a smaller engined bike can go through a given corner faster than a larger engined bike. There are too many variables to effect things. The smaller bike likely feels more nimble.
Its not so much the size of the engine as much as the weight
and length of the crankshaft for its the heaviest and fastest
spinning object in an motorcycle engine which acts as a
Gyroscope... Gyroscopes don't want to turn and once you do
try to turn them you get some immediate and strong
reactions... but if you spin the crankshaft backwards it will
cancel some forward spinning wheels gyro effect... you end
with a bike less stable in the straights but more willing to
change direction at the end of the straight... backward
spinning crank is the secret to Yamaha's MotoGp M1 but it
cost 5hp in extra shafts to accomplish...
Yamaha spins its MotoGp crankshaft backwards to offset the
long crankshafts gyroscopic procession and it's resistance to
turning... it gives the rider something the short forward
spinning crank V4 does naturally...
Given the same corner a longer crank has more distance to
travel than the shorter crank and with less distance to
travel means it takes physical effort and less time to change
Some Crankshaft weights I have on record... generally
speaking the lighter the crank the quicker the spool up the
quicker acceleration a rider feels...
RC45 11.2 lbs
RC30 10.8 lb
RC51 13.2 lb
CBR1000RR 18.0 lb
BMW S1000RR 16.7 lbs