I've never had a problem with the TRX-5 lacking bottom end, so with that in mind you might want to try either a Sparks TT or a Sparks MX. I would say the TT would be a tad better than the ESR pipe on the bottom, although it is mainly a mid range pipe. The only problem is that Sparks does not produce their 2-stroke pipes any more. You are gonna laugh, but maybe try a Pro Circuit MX pipe. I had one on my Open A Trx 330 built by Tom Carlson at TC Racing, and it was an awesome combo. The only pipe that was better was my Sparks TT BB pipe, and they are nearly impossible to find now-a-days.Which pipe would work best for MX/Dune riding? I'm currently running a TRX5 std. mount, 330cc with ESR low-mid porting. The TRX5 pipe lacks low end power and the TRX6 pipe is lacking on top end a little. Looking for something in between the 5 and 6 pipe. Is there an advantage to sticking with esr pipes to match the porting or would anyone's pipe work okay with the porting? I've mostly been considering Sparks, CT, PT, ESR, and LRD.