I ran a tuned .21 last season with little or no problems with the promo kit 2053 FLS type pipe and averaged 10-10.5 min in an 8T. It had more than enough power for the heavy truggy and the mileage was excellent. I switched the header to a long header from Ninja and that helped the bottom end out. Not the fastest engine but very reliable. So reliable that I purchased 2 more one tuned and one non tuned both powerhouse modded. I like the GRP's