Surely that would take a magician as to take something into consideration and take full advantage you'd need to have it on in the first place. They can't take a free flowing exhaust into consideration if it's not on the car so you will only get the results that the standard exhaust allows. Recently I fitted an FMIC but when I got my car mapped I never had it so they couldn't map the car based on the fact I was going to get one. This was a limiting factor on my car and why it doesn't put out the power it could. Now I've fitted the FMIC the car hasn't improved drastically as I never expected it to. However come the 4th September it will be another story after it's been back for tweaking.