Engine & Chassis

10-15 Years ago a lot of Products, would have made sense to be listed in this Section , but we write 2008 now , and the Market offers every range of horsepower which the customer may need. Best tuned Engines meanwhile come from Factory, and no avarage skilled Rider can reasonable say he wants more.
The Music of Performance next Decade will play inside the house of Electronics, making the Power more controlable, the Suspension (per Datarecording) more comprehensible.
If you would have a Datarecording you would be surprised what kind of 100% Throttle usage an avarage fast Rider on track has ( at a 1000cc Bike ) , it's somewhat 2-5% only , and the usage of the last 1000RPM before the Limiter comes is at 3-4% .

So a tuned Engine only is an advantage , if the Gain will be used. Considered the avarage usage above, considered a tuned Engine has 10% more Power , then you'd increase the Performance on track ( as a very simple broken down calculation) 0,3 -0,5 % . Or things even are inverted - people fear the Morepower and are even slower on track than before ( have seen more guys than one where this happened).
The rough Formula anyway  for a ~ 150 hp Bike at a 4km long Track is :
each + 20 hp makes a very good rider ~ 1.5 seconds faster. That's for guys who REALLY use the Power .
If you use 50% of it : 0.75 seconds faster.
If you do not use it anyway : Nothing.
If you fear the Acceleration : you're even slower than before.

So, as I see it , what could be left still to modify at an modern Engine , is close to nothing .
But to be more concrete , my suggestions :
1. decreasing the internal rotational Inertia , for better Acceleration , for better Handling, for less tendency of a hopping rearwheel at downshifting, means:
- lighten the Clutch , Clutchplates
- lighten the Alternator /Starter Drive /Flywheel and maybe crank ( but stop at a certain level )

2. Rider friendly Systems like slipper Clutches, can make riding comfortable,even they add a bit of weight sometimes .Because if you feel comfortable on a Bike, you're normally faster without even noticing it.

3. High Comp Pistons sometimes really can help at OEM low-Compression Models like Honda SP