oh yeah, i saw the other post, i think you answered your own question. a bigger diameter pipe probably wont help 'cause its a sonic thing, not a flow thing. i would try to modify the pedals to fit, or dent the pipe if you have to. sacrifice all for speed!
those estorils have a really sharp convergent cone at the end, which limits the top rpm really dramatically, you're not going to be able to get around that.