A buddy of mine from a local car board said that I shouldn't fear a "stack" because my 5" keeps the EGTs down. Is that true?

 

No, not at all. While it's true that excessive backpressure will raise egt's, having a huge exhaust system won't cure high egt's caused by more fuel than you have air for. The basic reason for this is that high egt's can be caused by several things, only one of which is backpressure. A 4" exhaust is adequate for all but the most powerful trucks. Thus, going to a 5" system generally is done for looks or sound, not egt reduction.

 

I saw a pretty decent drop in EGTs while cruising(and a small drop at idle) after I went to 5" exhaust(4" downpipe to 5" all the way back out, no muffler)
BUT I think what also contributed was the cat missing in action.
I did do it for sound and not performance(at the moment, later I might actually need it), but it has brought my EGTs down some, but also could have been due to the cat falling off.

 

well any drop at all is helpful I guess. I LOVE that sound of the 5" and that was the primary reason. I was just hoping for an extra benefit. thanks guys.