6637 question
Tuned
Joined: Jan 2005
Posts: 305
Likes: 1
From: Delphos, OH
I did the 6637 recently. My exhaust is stock with muffler delete (made a big difference in exhaust temps) I gained little to nothing in mpg. I did slightly reduce my EGT's when adding the 6637. Personally if you measure your exhaust it's measures about 3.5 on the outside. Most 4" pipes I checked measure 4" OD so that's a net gain of .5". I had a performance shop argue the point with me telling me my truck had a 3" exhaust standard. I told them if you can call your "system" a 4" I can call my stock pipe a 3.5" Where I'd like to gain which is where the 4" seem to shine is in bends and the down pipe from the turbo. If you want mpg gains keep the rpm's under 2000 at road speed. I hope this helps.
Senior User
Joined: Jun 2010
Posts: 362
Likes: 1
From: middlesex county, nj
Ouch....California, love the weather...hate, hmmmm...pretty much everything else ( no offense meant) we here in NJ have some strict rules as well...but my 11,200 lb gvwr allows me to circumvent all that crap,for now at least
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