Is a 4" downpipe worth it
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Postmaster
Joined: Mar 2004
Posts: 3,897
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For those of you that don't already know I am in the process of a major engine overhaul. Which also means there is a very large hole where my motor used to be. There's not very many write ups about a 4" downpipe on obs truck because it just doesn't fit. But with the motor out it wouldn't be hard to do the necessary firewall modifications to make it fit. I know Darin figured his egts were 50-75* cooler with his 4" downpipe that he installed and I ask you guys that are pulling frequently with bigger injectors, would you do it or not? As I said it would be easiest right now so I may already have made up my mind but I am looking for other opinions. Thanks. Nick
Hotshot
Joined: Feb 2009
Posts: 10,408
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From: Plankinton, SD
Nick, if you have the time, now would sure be the time to at least make the room for one if you think you'd want one. Knowing it did help my egt's I'd do it again in a heartbeat. It was quite a bit of work, but means it helped I call it worth it. Now this is with a bigger turbo, I don't know how much it would help on a stock turbo. It sure wouldn't hurt, but I don't suspect that the difference in egt's would be as much.
It's all up to you. Even if you made the room and didn't go that big you'd have real nice clearance on a smaller one. Mine goes to 5 inch as soon as I could. My elbow shooting it to the back is 5 inch and the adapter to 4 inch is above that, then 4 inch the rest of the way up. Like I said, it is quite a bit of work between the downpipe and firewall modding.
It's all up to you. Even if you made the room and didn't go that big you'd have real nice clearance on a smaller one. Mine goes to 5 inch as soon as I could. My elbow shooting it to the back is 5 inch and the adapter to 4 inch is above that, then 4 inch the rest of the way up. Like I said, it is quite a bit of work between the downpipe and firewall modding.
Elder User
Joined: Sep 2004
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Nick, if you have the time, now would sure be the time to at least make the room for one if you think you'd want one. Knowing it did help my egt's I'd do it again in a heartbeat. It was quite a bit of work, but means it helped I call it worth it. Now this is with a bigger turbo, I don't know how much it would help on a stock turbo. It sure wouldn't hurt, but I don't suspect that the difference in egt's would be as much. It's all up to you. Even if you made the room and didn't go that big you'd have real nice clearance on a smaller one. Mine goes to 5 inch as soon as I could. My elbow shooting it to the back is 5 inch and the adapter to 4 inch is above that, then 4 inch the rest of the way up. Like I said, it is quite a bit of work between the downpipe and firewall modding.
Hotshot
Joined: Feb 2009
Posts: 10,408
Likes: 75
From: Plankinton, SD
I don't know who sells a 4 inch DP for these trucks, mine is a diamond eye super duty 4 inch downpipe modded to fit and then pieced together with a 4-5 adapter, 5 inch elbow, and some 5 inch stock, adapted to a 5 inch diamond eye catback system. SD downpipe has the right flange for my S366 turbo. No cat, just bought that system as it would work with what I was building in front it, muffler is in the stock place.
Elder User
Joined: Sep 2004
Posts: 510
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I don't know who sells a 4 inch DP for these trucks, mine is a diamond eye super duty 4 inch downpipe modded to fit and then pieced together with a 4-5 adapter, 5 inch elbow, and some 5 inch stock, adapted to a 5 inch diamond eye catback system. SD downpipe has the right flange for my S366 turbo. No cat, just bought that system as it would work with what I was building in front it, muffler is in the stock place.
Hotshot
Joined: Feb 2009
Posts: 10,408
Likes: 75
From: Plankinton, SD
That's a real good system. I'm sure you will be happy with it.
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Cargo Master
Joined: Feb 2009
Posts: 2,111
Likes: 0
From: Yreka, CA
That's the same system I have. Clearance is a little tight around the spare tire, but I love it.
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