If I have the standard exahust and everything, but have a Mugen Header+ARC Intake, will my car run leaner? If so, is that really bad?

 

Ummmm no.
But why did you get a header before exhaust? Just wondering.

 

The header came in at a very apealing price and I knew the previous owner so I knew how long he had it for. It was like $1000AUS, so quite good price I think.
I havnt done an exhaust yet, but planning on getting the new Mugen one, just the price is kinda ugly.