When it comes to a more freeflowing exhaust how much is too much? Can you cross the line from freeing up power by way of increasing the exhaust flow to actually losing power because you freed it up too much?

Where's the line? Anyone with heavily modified exhaust i.e. headers, test pipes, etc. had any backpressure problems?

 

If someone says backpressure creates torque, I'm going to reach through my monitor and smack them

The key to a good flowing exhaust and/or header system on a naturally aspirated motor is exhaust velocity. High exhaust velocity while keeping the exhaust gases hot is much more important than an increase in area.

Yes, it is very possible to make an exhaust too large and cause a performance loss. Lots of people that don't know any better, think bigger is better and they put huge exhaust piping on their cars. What they notice is a complete lack of power in the low to mid range and then the car wakes up. What happens is the exhaust velocity in the lower to mid rpms becomes turbulent in the big pipes and cools down causing low exhaust velocity and lower power. Then once the rpms rise, the velocity improves somewhat and the power they lost is restored.

On a 3.5 V6, there is no real need to go any larger than about 2" on a true dual exhaust and 2.5" on a single pipe exhaust. Ideally, you should taper or step the exhaust towards the exit point. This means starting with a larger at the beginning and work the piping diameter down fractionally has you get closer to the exit point. I know this isn't what most people have heard or read about on the internet, but it's the truth.

 

Yes I think DaveB is right on. For example many exhaust builders will tell you that a 3" dual system is too big for these engines, unless you are running FI in which case you want as much flow as possible.

 

Yep! Forced induction can move a ton of air so it can take advantage of huge pipes.