but I don't understand how you get higher boost #'s with having more flow out the exhaust ???
4" exhaust rules
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Postmaster
Joined: Jan 2009
Posts: 4,006
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From: AL, Reform
4" exhaust rules
i put a 4" Silverline SS T304 Turbo Back on and i think my stock one most have been plugged up, and it sound great. i can get more boost and have gone from 14.5mpg to 17.2mpg 
, and this is all i have changed. just to get the winter blend out of the way i fill from a tank on my farm that is the same fuel. there is a big hill on the road i live on that at 35mpg i was at 4psi now it is 9psi and i can get to 19psi by just tapping the gas. i have all was wondered why my truck got 14,mpg when my dads and brothers got 17mpg, it most be my exhaust was plugged up.
, and this is all i have changed. just to get the winter blend out of the way i fill from a tank on my farm that is the same fuel. there is a big hill on the road i live on that at 35mpg i was at 4psi now it is 9psi and i can get to 19psi by just tapping the gas. i have all was wondered why my truck got 14,mpg when my dads and brothers got 17mpg, it most be my exhaust was plugged up.
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
My truck has a shiny new 4" and I have an AE. I'll be taking measurements for a while to see if there is any engine data to show a difference. It sounds a little louder in the cab and I can get a slight drone if I were to tow or climb a hill, but the drone is not obnoxious. I have too few miles on the new system to give solid answers.
More Turbo
Joined: Jun 2010
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From: reedsport
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Lead Driver
Joined: Nov 2007
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you could have 10" exhaust it it would matter much since im sure your down pipe is still only 4inch.
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Logistics Pro
Joined: Dec 2010
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From: Temperance, MI
This doenst make a bit of sence to me......... You dont get +3 mpg by doing an exhaust on anything..... and it shouldnt make a difference on boost either because the only way boost goes up is when fuel is added....
It is what you say it is congrads, Im jealous because it made no difference in my mpg
It is what you say it is congrads, Im jealous because it made no difference in my mpg
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
This doenst make a bit of sence to me......... You dont get +3 mpg by doing an exhaust on anything..... and it shouldnt make a difference on boost either because the only way boost goes up is when fuel is added....
It is what you say it is congrads, Im jealous because it made no difference in my mpg
It is what you say it is congrads, Im jealous because it made no difference in my mpg
My best guess is "it depends". If mods were made to feed more fuel and air, but not let the air out - there should be a noticable improvement with bigger exhaust. If one put a 4" on a stock truck, it would be more for sound or looks or something other than performance. This would explain why some people rave about this mod and others feel like they've been ripped.
Logistics Pro
Joined: Dec 2010
Posts: 4,738
Likes: 15
From: Temperance, MI
Boost is driven by the flow of air through the exhaust side of the turbo. Block the exhaust completely and there is zero flow to turn the turbo for boost. Reducing backpressure allows the air to flow more freely on the drive side of the turbo, which can give just a little more boost and/or spin the turbo up quicker. What I don't know is if this difference is perceptible
Now if your truck has a cat. and a muffler and you go to a straight pipe your still not going to get any more boost, but you do reduce back pressure and it will spool faster but thats it. Like I said before the only way to increase boost is to add fuel
Matt did you happen to notice that the stock exhaust was actually plugged up? Or was that a hunch?
Veteran/Sheepdog
Joined: Feb 2012
Posts: 6,047
Likes: 110
From: Western AR
My upgrade to 5" exhaust gave noticeable gains in power (I'm betting 20HP). Truck runs much better and turbo is functioning more efficiently (faster spool-up). I have not noticed a gain in MPG's, but I put a Walker BTM and a FTE resonator on to eliminate drone.
Mike
Mike
Tuned
Joined: Oct 2011
Posts: 282
Likes: 0
I just put on my Magnaflow 4" today. Getting the old one out was the hard part. Putting the new one in was pretty easy and the fit was great. It has a deeper tone but not much louder which is what I wanted.
Boost does seem a little higher just driving around town but nothing drastic. The real test will be when I pull my trailer. I wasn't expecting anything major but I wanted it to breath better.
Boost does seem a little higher just driving around town but nothing drastic. The real test will be when I pull my trailer. I wasn't expecting anything major but I wanted it to breath better.
