Spur 37/and Pinion 23 all from HPI and yes and OS 18tz woth a good pipe, but seems that HPI is not making spur37 anymore.
I started to use Losi's 19/26 pinion/clutchbell with HPIs 37/43 sours and they mesh correctly.
Look at my vids.
http://youtu.be/-u-ZAyMXw_w
keep looking under my youtube file, theres more speed runs and dragracing