10 mins is pretty hard to get with a .28, what pipe combination are you running with your .21? i found with a ttr 2035 and os p3 plug and 7mm restrictor the grp had plenty of low end power for the truggy, the 2053 that came in the promo kit didnt seem to have the bottom end power, i dont think any of the factory drivers run the 28 in there truggies