Hey Sportsfans,
My opinion as to your question of Boxster Balance (mightyfine) after my power upgrade to 355+HP:
Balance
The nice static balance is hardly changed at all. The new engine is very close to the same weight. The low center of gravity mid engine configuration is intact. The Boxster S drive train is able to put the extra power to the ground strong and smoothly, no hop, chatter, or twist. This is not adding a 327 to a Vega
Adding a girlfriend can upset the balance more.
Driver Input
There is the matter of Driver Input though. With more power available, the course of the car can be altered around the apex by exceeding the rear tires' ability to grip the road surface. The rear tires have to grip under both the forward (hammerdown) and lateral (oh $*# guardrail) forces. Crudely, the butt can step out if you mash it in a hard turn. Again, this is not a balance issue to me, but a driver input. This is a skill that is so fun to learn, potentially disasterous if in error.
Better Balance under Power
Better tires can increase the overall balance under power. I have a suspension upgrade that lowers the center of gravity, supresses body roll and tends to keep the inside tires with stronger contact, improving the "balance" under power and lateral loads. For the same reasons, the stock S model is better than the base model under these conditions.
The addition of a Limited Slip Differential &/or Traction Control can keep the rear tires in better contact under power, hence better balance. I will defer to the true gearheads of this forum as to the availability of these options on the 986-7. A great illustration of this interaction between balance and power could be seen when F1 eliminated traction control this year!
My power lunch is up, its back to the shed for me. :dance:
Hasta,
Ike