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Originally Posted by willief350
Is there a clear ideas as to 3.5 or 4" downpipe?
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The only difference between a 3.5" and a 4" downpipe is about a half inch.
No difference in performance for normal truck duties such as towing a boat or trailer with something like a 60-tow tune, or a total of around 300 horses.
The outlet from the turbo is 3", so whether you expand it to 3.5" or 4" doesn't really matter until you get up over about 400 horses.
So for your exhaust, the least-expensive fix is to replace the muffler with a Walker BTM (big truck muffler). Or if you can stand the racket and don't mind being illegal in most jurisdictions, then a straight pipe to replace the muffler. Next up the cost chart is an aluminized steel performance exhaust system. Another notch up will get you my "ugly" stainless exhaust system. And top of the line is the shimy chrome-like stainless exhaust system. All three performance exhaust systems will perform the same. The steel will rust after a while. The shiny stainless will impress your grease monkey in the grease pit at Wal-Mart. The ugly 409 stainless is my choice. It will last forever, even though it will have some ugly surface rust, and nobody but me and my grease monkey will ever see it.
If you're trying to build a turbo-back exhaust system piece by piece, you'll probably spend more money than by simply buying an off-the-shelf kit by MBRP or Magnaflow or Banks. Whether the downpipe expands from 3" to 3.5" or 4" doesn't matter - buy the one that's cheapest and matches the rest of your exhaust system.
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Should I DIY it, buy it, weld or bolt on?
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I would buy the turbo-back kit, then DIY. If you don't weld, then take it to a muffler shop and pay them to complete the installation by welding the connections up tight.
All the pros bolt it on with muffler clamps, then they weld up the connections. Some amatuers might do one or the other, but the pros do both.
SO DIY with muffler clamps, but then finish the job by welding it on right.
Last I heard, if you call the folks at the following link they will sell you a 4" turbo-back stainless performance exhaust system for less than $300.
Performance Truck Products - Home
But his best price is only by phone. So call him and tell him you're a member of TheDieselStop and he'll take care of you.
