Well im stuck for ideas on why my car is 3kmh down in trap speed. For the past 5 times i've raced my car has only done a best of 13.9 @ 160km/h. When before that it did a 13.6 @163.5km/h. My 60ft has been the same if not better due to having semi slicks now (the 13.6 was run on street16'' tyres the same rolling diamete)r. The only things that i have changed since running the 13.6 is underdrives a hole in the air box and a different brand of fuel filter (now genuine). The car is serviced every time i race including air filter clean and throttle body clean, and spark plugs and fuel filter are changed every 15,000k. The only thing i can pin it on is maybe my last tune isn't up to scratch, the coopers fuel filters flow better then factory ones or the underdrives are causing a torque drop. Any ideas?

put the street tyres back on it and run it again.. The slicks may be bogging you down off the line a little hence affecting your mph..

put every thing back the way it was and run it. if you pick the MPH back up, then only change one thing at a time.

If you don't pick the MPH back up, then for some reason you are down on power.


What pressure are you running the new tyres? and are theyreally the same size? or is it just size on the sidewall is the same?