8 minutes is a fairly good runtime for a tank (you do not state which track, which car, pipe/manifold combo and what are your traction conditions).
The key for more runtime sometimes is your throttle finger. Being gentler on the throttle makes much difference.
Maybe you can try with a lesser powerful engine. Sometimes, power is not everything...
Edit: Readed you signature: Have you tried with a Sirio pipe?. That nasty habit of Mix & Match engines and pipes from different manufacturers ruins all the work from the engine maker.
[quote=MugenDrew;2684554]BATTERIES are for FLASH LIGHTS, gasoline is for cleanin parts, alcohol is for me to drink and well NITRO...everybody know thats for racing.[/quote] :D:D:D