Yet another exhaust question.

bigger pipe allows more air flow,so it will drop your exhaust temps, and your turbo will spool faster. I just installed a 4" downpipe with 5" straight pipe and it opened it up quite a bit. And even with no kitty and no muffler it is still quiet. All I hear is my turbo.

The cat is the big killer once that is removed you gain alot more hp Id say 80% and 20% for thge muffler . Honestly if you put a 4inch on the diameter wont make a big difference. However the stock muffler doesnt go straight through it has some dividers in it. If you can get a 3.5 straight muffler or a muffler delete that could help ya some.

i ran a straight exhaust on my truck using the stock exhaust and it did a great job unless you add more then 120hp extra it won't really gain you anything to do a bigger exhaust or unless you want the look and sound of a bigger pipe.:cool ..i now have a 5" T/B exhaust,i just had to have a bigger pipe,plus i love the sound :rockin

If memory serves me, every inch in diameter doubles the amount of air the pipe can flow. So, yes, going from 3.5 to 4" can really make a difference. Also, most aftermarket mufflers are 4". I would do a turbo back 4" and its up to you if you install the muffler. The muffler won't really affect flow much, its all about the sound you want. Personally, I think straight piped LB7's sound sweet!

Thanks for the advice fellas. I've been a member of a few forums but this is the best one by far. Quick answers and honest answers. Love it.