My low speed rating experiment was largely a failure.
I bought a Shelby GT500 and put a bunch of power parts on it. Things were looking good; my PI went up very slowly as I added parts and my speed rating stayed at 3.0. I could get 20HP for something silly like 3PI. I ended up with as many power parts as I could get building up to 425PI, and added race brakes, a rear diff, aero, and a little bit of tire for good measure. The car was an easy drive, but it topped out very low... I forget the max speed, but it was something like 120mph. Even with all that power, the car was way off the pace on my test track (Catalunya National). I spent half the straight on the rev limiter.
I bailed on that and bought a Chevelle (did I mention these muscle cars are draining my bank account?). Same deal: got a bunch of HP for not much PI. But the result was the same; not a class killer, at least in C. The Chevelle WAS pretty close to my top time, however.
Next I went looking non-muscle cars to work the same treatment on. Surely there are some highly gear-limited euro cars out there? I tried my Abarth, but as I added power its top speed went up. Same deal with the 60's Z. I'm starting to lose interest....
Last ditch I grabbed my Dart Super Stock, wiped its tune, and added the mythical Viper swap. Sure enough, I dropped from C class to E class with the swap, but added horsepower and reduced weight. I started adding power parts and found that I could get 50HP+ boosts for 1PI. Ticking off all the power boxes I eventually added power for ZERO PI. The only part I couldn't add without increasing PI was the cams, which makes sense. I finished the car off by adding some suspension/brake/weight upgrades (weight was also nearly free) and had my 900HP, 2500lbs car ready to drive. In E class. YIKES.
I took the beast to the track and quickly found that the only gear worth using was fourth (top gear). The car handled OK, its only problem was that it topped out at 110mph. Well, the other problem was that it had so much power that hitting 110mph was difficult; I had to be glacial on the throttle to avoid wheel spin. I was basically traction limited to top speed. (Perhaps the drag tires would have been an advantage?)
I ran a couple laps on Catalunya National to benchmark. Along the way I found that I could hit 110mph within about 60ft of the last corner exit, and carried it--slowly, and painfully--all the way down the main straight. My best lap time was six seconds SLOWER than my best car in E. I tried adding stickier tires and such to improve the car, but I only managed to bump myself up to D, where the competition was stiffer.
With all that power, if I added even the sport tranny (adjustable final drive) I was kicked up to A and beyond.
In the end I'm more confused than when I started. What parts are the goofballs using to make the Dart a leaderboard killer? Why doesn't it work on other cars? The engine swap clearly plays a role, but I could not replicate this phenomena with the other cars. It appears the PI system is pretty sound with the cars I tested, but it seems I'm not doing SOMETHING right.
I guess I'll just go back to racing for fun and stop trying to peel the skirt back on the seedy underbelly of Forza leaderboard stacking. Woodward and Berstein would be ashamed.
