(I posted this in another thread, but it seemed like it could use it's own)
I know this subject has been beat to death, but no one has ever been able to answer this to my satisfaction.........

For those who insist that fuel management is a must with just slip on's.......

Answer me this:

An engine is basically an air pump....suck, bang, blow.....right?

So, if you decrease the restriction of the exhaust by adding free flowing mufflers.....

WITHOUT increasing the amount of air intake by adding a hi flow AC.......

How can it make the fuel mixture leaner than it already is if it's not getting any more air?

 

Electronic fuel management may or may not be able to compensate for less restriction in the motor. The exhaust plays a huge part due to tuned effect which can alter airflow several percent. A well tuned race engine can see the motor actually taking in 1.3 times its own displacement in air volume due to the overall tuning effects which use momentum, suction, airflow velocity and valve timing to "trap" the most air possible at a certain rpm. The exhaust does its part by providing a resonant wave that goes back up the pipe to create a partial vacuum at just the right moment. If you change the exhaust in any way, you change the amount of "vacuum" it can provide, and when.
Obviously a street type motor won't see the high percentages of increase i mentioned, but you can understand how it affects even a stock type motor.

 

I have been wondering the same thing as you are but I was wondering about the oppissite modification. I am compleatly satisfied with the way my 07 WG runs, performs, etc but would like to change the A/C to something other than the stock football cover. Maybe Big Sucker with open cleaner or Heavy Breather for appearence more than anything else. Has anyone done this and had the tuning checked?

 

Your air filter and exhaust are designed to flow up to ~5500rpm. At that point you could be correct in that the filter and/or exhaust has reached it's maximum flow. But, at say 3000 rpm, your new exhaust is flowing more and your filter can flow more (it's not at it's maximum flow rate yet) and the result is a leaner mixture.

Jim

 

What's more, is the way the components flow on their way to their maximum. If there are any changes to the curves from the way the stock parts flow, some slightly weird stuff will happen with the tuning. This is because we currently have a form of auto-tuning which was intended for whole-system correction. It will "sense" the various changes of the new parts and adapt as best it can, but in the process can do things like remove fuel from a place which actually requires more, or vice versa.