Understand that. The xp1k I have also has an oxygen sensor. So it should have a variance built in to the factory ecu. The older bikes, I understand use map sensors only which I would call closed loop speed density in the auto world.Simple..automotive closed loop systems monitor AFR and other parameters and make fuel adjustments automatically..SXS"s dont. Proof is in dyno or real world AFR logging. I run a wide band AFR and can tell you that there is a difference in AFR even with just a filter change...maybe not much but there is. All exhaust flow different and need thier own fuel curve. Some fuel added in one rpm area and maybe some taken away in others.Can anyone offer a legitimate explanation on why a fuel controller would be needed for an engine with only an exhaust mod? I have extensive car knowledge on big v8s and am aware how the air/fuel ratio changes with this mod and usually is lean. But in a big motor making 20-30 hp more vs this 2 cylinder making maybe 2-5 hp. I'm looking for hard evidence of back to back air fuel ratio changes adding exhaust only without a fuel programmer.