I had Arrow headers and stock silencer on my ST but only because it sounded better. Data logging showed very little change to VE, so no real difference in flow as you’d expect with no intake changes, but the stock fuel map was too rich outside closed loop, as is the case with most bikes. Although there was no need to remap, disabling closed loop, leaning out fuel maps at wider throttle openings/revs, more progressive throttle maps, smoothing and slightly advancing spark tables, getting rid of fuel cutoff, increasing the accelerator pump table values from the US spec ECU and reducing engine braking all combined to make the bike more responsive and better to ride (as would have been the case with stock headers). The guy at Wiz (Grant?) has some proper Ftecu Flash Tune tunes that have been dyno developed for the ST. Unlike Hilltop who are charlatans because there is no remap, just a hard ecu reset by idling the bike until the fan kicks in (yes, I’ve watched him do it!).
