Going "FAST" with a pan car is easy - keeping it on the ground w/o going airborne, or simply spinning out....another story.
Pan cars need clean smooth surfaces - any dirt/dust makes them a handful really quick.
Depending on the radio you have - you can go with something like a 1 cell lipo battery - and a 10.5 wind motor. That will give you a good speed range, and if it's too fast to start you could simply turn down your Throttle end point to adjust to a desired speed.
If you already have 2 cell packs that will fit the chassis - you could still go with a 10.5 wind motor, but that combo in the right place w/ the right gearing will top 70 mph . 2 cell and a 17.5 wind motors ran over 60 mph on high banked oval tracks several years ago (BICYCLE VELODROMES)
Depending on what body type you plan to use on this, make sure to use a fairly large wing or spoiler on the back end for more enjoyable "bashing", it will really help keep the rear tires planted to the ground.
R/C Racing since 1985 ~ Santa Maria, CA (Central Coast)
2001-2012 - South-West Tour R/C Oval Series - R.I.P.
...will the SWT be revived? Time will tell, but we ARE returning to the VELODROME in 2016