My buddy has FMF fatty's on his banshee before it was ported. Strait up garbage to ride. But that doesnt mean they are bad pipes. They are good pipes.
Id like to see some videos of you racing your buddy and you racing by yourself. I want to see how good you are speed shifting, shifting, launching, riding etc. Driver skill is huge on a banshee.
Id hate to recommend other mods if the problem is you.
And 170psi seems high. Some lower octane race fuel perhaps might bee needed. But if you arent detonating, then i guess you are fine. Compression gauges vary. Mine was at 169.5 and i melted my pistons.
As for running a train on that yfz450, not in all cases. There's a lot of variables here.