Squidmonkey,
The Fit was designed to be one of the world's best handling fuel efficient cars... I'm not sure if you know this but the handling characteristics of the FIT is so good that not only was it best performer in it's class (other similar situated priced cars) but Road & Track reported that it outperformed a current model year Corvette.
I know that you asked above about adding horse power to the car. However, as gleamed from the above posts, adding horsepower is not always the best thing to do.
Even better is to know the strengths of you and your car and to know and challenge the weaknesses of your opponent and opponent's car.
If you look at the parts listed in JamesBizzel's signature you'll see light weight wheels (around 10lbs/wheel) and a lot of chassis braces. I think that JamesBizzel understands that the way to make the FIT faster is by replacing heavy items with light weight ones. In addition, stiffening up the chassis will make the car respond to directional input faster and the car will be more stable and consistent under the new directional input.
I wanted to share with you something special. It doesn't involve adding horsepower. However, it probably will costs as much as if you added a J's racing titanium (very light weight) exhuast system to your Fit. And when you learn how to drive your car (performance driving schools or whatever) you'll be several seconds faster than if you didn't have this part on.
The part is a Limited Slip Differential for your Automatic Fit. This part is special to Automatic Transmissions because in the past LSDs were incompatible with ATs. Please see the following quote:
"Compatible with Automatic Transmission Vehicles
(Noiseless High Performance with Automatic Transmission Fluid)
In automatic transmission vehicles abnormal noise is unavoidable with a metal LSD, but Carbon LSDs will adapt without any problems to the fluid used for automatic transmissions. It is for this reason that an LSD for use in automatic transmission vehicles is now planned for our company's product line. This will enable sport driving with automatic transmission cars, and will also be extremely effective in improving the quality of the ride over poor or snowy roads.
[Explanation]
Development of an LSD for use in automatic transmission vehicles has been attempted many times in the past, but the compatibility of LSDs with ATF (automatic transmission fluid) has been poor and operation was abnormally noisy, so development was abandoned. However, the results of compatibility tests of carbon LSDs with ATF have shown that there is absolutely no problem with locking performance and noise, so we have embarked on the development of a carbon LSD for automatic transmission vehicles.
In December, 2005, we will release the first carbon LSD for automatic for Honda Fit 1,300 & 1,500. ATS carbon LSDs will make your automatic vehicles or mini vans really lively and nimble without sacrificing any riding comfort. "
Link is here:
http://www.a-t-s-usa.com/ats-products/lsd-carbon1.htm
Please do a search and look at how Ben set up the AJR time attack Fit. The AJR Fit did extremely well (2nd place) at this year's time attack at Buttonwillow. I talked to Ben and he thinks that with a couple of more hours of dialing in the suspension they could have shaved 2 more seconds off of the Fits lap time and taken first place (Upsetting all of the high horsepower Fits) at this year's timeattack.
Good luck with modifying your car... If you have any questions please don't hesitate to pm me.
Lance