Brian. I had the 521 out last weekend, It ran fine. was very hot day on sat and ran a best 6.43 which is what I expected. Sunday cooled a bit and the first pass was a 6.35 WOW! A little to fast fot the chassis. So I started backing off the timing and ended up winning my class at the end of the day. everything worked good but it has a small miss in the burnout box but i dont notice anything during the pass. So she's out and running as good as I expected and better. Thanks....Bud!