I read and hear all the time that ......
1) I drilled out my exhaust
2) took the mufflers off
3) added new performance pipes
1) I added a hi flow air filter
2) removed the rubber seal around air filter
3) modified air intake
The story usually goes like this .... They did one of the above mods and either the bike is running worse, hotter, popping or it did nothing.
I'm not a mechanic or rocket scientist although i fixed the toaster the other day
But in doing one of these simple mods on its own .....it will put your engine into a LEAN state for one. It can also cause a loss in back pressure and cause some extra popping on deceleration.
Today's fuel injected bikes are already set up to be in a lean air/fuel ratio to meet EPA numbers set by the powers that be. I think it's 13.6 to 1. And I believe the newest numbers may be 14 to 1. My point is Lean from the factory. Running lean engines make them run hot and if tampered with in a worse case scenario can melt a piston.
Engine mods need to be done as a package deal and air/fuel management has to be apart of any engine mod. We all want our bikes to sound just a little better and run a little faster. But by just adding more air you will lean the engine out more. Or adding new pipes you will lean the engine out more. Or just doing both .... Well you get the picture.
There a neat little mod for the Victory where you drill out the plate up the pipe with a 1 1/4" hole .... And you add a K&N type filter and then you disconnect the exhaust sensors. This is a cheap package deal, but in essence covers all three things you need to be concerned about. First your allowing more air in to cure the bikes asthma problem
second your letting the air out to balance the flow. And thirdly your managing your air/fuel mixture by disconnecting the exhaust sensors. As when they are disconnected the bikes computer goes into safe mode and richen's up the mixture and takes it out of that too Lean state caused by adding more air and exhaust.
I'm not saying this is the best idea but it works and is cheap and covers all three issues when doing an engine mod.
The better way to go is obviously add a good air intake system, add good pipes made for your engine and add a fuel management system like a Power Commander or whatever. This is a package and will keep everything running as it should and as cool as it can with that little bit more of get up and go.
Just my thoughts hope it helps