***Note: I've heavily searched this topic, but there are too many conflicting "oppinions" and not enough facts.... Brent.***

I will be replacing my factory muffler with a Flowmaster 40 Delta within the next week and I have some questions about the factory exhaust.

I got underneath my truck yesterday (2004 XE-V6) and measured the circumference of the exhaust tubing just before and after the factory muffler, which was roughly 7.1".

Remembering back to middle school math:
C = 3.14 X D

Therefore the diameter = ~2.25"

Calmini runs 2.25" tubing from the flange back.
Magnaflow runs 2.5" tubing but it appears to start at 2.25" near the flange.

I would like to use a 2.5" Flowmaster muffler using a step-up from 2.25" to 2.5" after the flange (before the muffler) and after the muffler run 2.5" the whole way back to the tailpipe.

Here are my questions:
1. Would I see a benefit in performance or exhaust tone by using 2.5" tubing after the muffler?
2. Are there any disadvantages by using 2.5" instead of 2.25"?
3. Or, should I just use the factory 2.25" tubing size?

Anybody....

Bueller....

Bueller....?

Since nobody is responding... I have heard this before, and I may be wrong. But if you increase the circumeference of the exhaust, which is turn provides more airflow, wouldn't that decrease the backpressure in the exhaust? And doesn't decreasing the back pressure produce a loss in torque? Technically it makes sense, you would want the Xterra to has the least amount of resistance from any part of it's engine, so that it can rev quicker. But I don't think that the Xterra engine is meant to rev quick. I think it's meant to rev slow and produce as much torque as possible, not hp. I may be wrong, and I'm going off of a whim here, but to me it makes sense.

I've always understood that same to be true... which is why I question companies like Magnaflow which produce 2.5" exhausts instead of the factory size.

Stick with the stock size. Its cheaper, and you wont notice any difference.

In reality when considering a 1/4" difference exhaust size anywhere but in the primary down pipe from the exhaust ports on the heads, in the amount of power production that the Xterra produces you will experience no discernable difference.

Basically it doesn't matter

Thanks Mui Malo!

Just to make sure my measurements are correct and I don't order the wrong muffler, the stock size after the flange for an XE-V6 is 2.25" right?

I found the answer to my own question here if anyone else is interested...

http://www.xterraownersclub.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=001935#000001

Wow, I got it before Brent did!?