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Which Downpipe?

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Old Apr 20, 2004 | 09:02 AM
  #1  
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Which Downpipe?

I'm looking at this group purchase deal going on with a 4" exhaust, and I'm not sure which would be better go with, the 3.5" downpipe or the 4"? I've got a '99 F-350, assuming it's a 3" downpipe. I've read that the 4" will move the torque curve up the power band, and it will feel like you don't have as much power at the bottom end. Is it more difficult to install the 4" over the 3.5", or is there plenty of room between the firewall to get it in there?
Any info or advice would be great! THANKS!
 
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Old Apr 20, 2004 | 09:19 AM
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I can only answer part of your question. I have a 4" down pipe and I had no clearance issues (2002 PSD) and didn't have any problems putting it on. I too have read about the 3.5 versus 4 down pipes but I don't know what to think. I can't say that I noticed any loss of power down low when I put my exhaust on but that is my personal experience.
 
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Old Apr 20, 2004 | 09:31 AM
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Unless you are going to juice up your PSD with a big chip or propane, the 3.5" will move all the air that you need it to.

The muffler is the main restriction on these trucks. Many people report very good gains by just changing the muffler to a free flow setup, like a Walker BTM, and leaving the stock 3" DP.
 
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Old Apr 20, 2004 | 07:15 PM
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I agree the 3.5 will suffice, then go to a 4" exhaust from there.
 
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Old Apr 20, 2004 | 09:39 PM
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I've had both. The percieved power loss from the 4" was negligible, and the EGT's are better with the bigger pipe. My vote is for the full 4".
 
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Old Apr 20, 2004 | 10:59 PM
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which downpipe do you guys recomend to go with on a '96 PSD automatic? i have straight pipe under her right now and im loving it but i want to do downpipe and im wondering what to go with, any help would be greatly appreciated
 
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Old Apr 21, 2004 | 08:42 AM
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3.5"dp,anything larger and you will have clearence issues.
 
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Old Apr 21, 2004 | 09:48 AM
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Originally Posted by bender97f250
3.5"dp,anything larger and you will have clearence issues.
No you won't...I have a 2000 and I had absolutely NO trouble getting the 4" dp in. I could have gotten a 5" in there and still not be rubbing the firewall.
 
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Old Apr 21, 2004 | 11:05 AM
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Originally Posted by majorpecs
No you won't...I have a 2000 and I had absolutely NO trouble getting the 4" dp in. I could have gotten a 5" in there and still not be rubbing the firewall.
Right, but the 96 in question has a different firewall, different turbo mount etc. A 4" down pipe will not fit a 94-97 without some modifications. I've heard the 3.5" can be a tight squeeze.
 
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Old Apr 21, 2004 | 02:57 PM
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Powerstroked 162 specified a 1996,to use a 4"dp,you will have to modify the firewall.The 3.5" is a snug fit at the bottom of the firewall also but works.
 
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