Made my own 4" Downpipe
Thread Starter
Registered User
Joined: Nov 2005
Posts: 1,971
Likes: 1
From: Land of milk and honey.
Made my own 4" Downpipe
A website sells 4" downpipes for $198 plus it was $52 to ship...>>>$250 Total.
I bought some fittings and a little time with my chopsaw and my mig welder, made up a 4" downpipe.
I cheated a little in that the cab is off the truck right now. So it was very easy to cut and tack pieces matching things up trimming and shaving with nothing in the way.
My main concern was making that first 90* turn off the turbo with enough clearance. I actually made the turn about 3/8" tighter on the outside closest to the firewall than the factory pipe.
This is a list of what I used...
4" OD to 3" OD reducer
4" OD OD 90* short radius (4" centerline) mandrel sweep
4" OD OD 90* long radius (6" centerline) mandrel sweep
4" OD OD 30* long radius mandrel sweep
$75 total
First, trim the clamp flange section off the original pipe. I cut it where the first visible ridge is where it expands a little (about 2" long).
Cut the 3" to 4" reducer as tight to the reducing section as possible on both sides. I was able to do this using less than 1" of run. Then cut one end of the 90* short radius as close to the turn as you can get. Leave the other side long.
The original clamp flange section fits nicely into the shortened reducer.
I then shaved one end of the long radius 90* on about a 10* angle. I kept matching it up till it looked good. This accounts for the little offset "jag" you need to be centered between the bell housing and the chassis. With a 10* angle on one end,the pieces matched up nice.
I then used the 30* elbow with a slice to drop down and get level again below the transmission crossmember.
I started welding it all up but my spool ran out of wire. I'll finish it in the morning.
I bought some fittings and a little time with my chopsaw and my mig welder, made up a 4" downpipe.
I cheated a little in that the cab is off the truck right now. So it was very easy to cut and tack pieces matching things up trimming and shaving with nothing in the way.
My main concern was making that first 90* turn off the turbo with enough clearance. I actually made the turn about 3/8" tighter on the outside closest to the firewall than the factory pipe.
This is a list of what I used...
4" OD to 3" OD reducer
4" OD OD 90* short radius (4" centerline) mandrel sweep
4" OD OD 90* long radius (6" centerline) mandrel sweep
4" OD OD 30* long radius mandrel sweep
$75 total
First, trim the clamp flange section off the original pipe. I cut it where the first visible ridge is where it expands a little (about 2" long).
Cut the 3" to 4" reducer as tight to the reducing section as possible on both sides. I was able to do this using less than 1" of run. Then cut one end of the 90* short radius as close to the turn as you can get. Leave the other side long.
The original clamp flange section fits nicely into the shortened reducer.
I then shaved one end of the long radius 90* on about a 10* angle. I kept matching it up till it looked good. This accounts for the little offset "jag" you need to be centered between the bell housing and the chassis. With a 10* angle on one end,the pieces matched up nice.
I then used the 30* elbow with a slice to drop down and get level again below the transmission crossmember.
I started welding it all up but my spool ran out of wire. I'll finish it in the morning.
Trending Topics
Registered User
Joined: Oct 2009
Posts: 1,830
Likes: 1
From: Claymont, Del and Horsham, PA
Nice work, this is what i need to do!!!
Need to get a different flange though....did you use a flux-wire(what i have) or gas shielded mig? I'm thinking a gas-shielded would be better because of the extreme conditions.
Need to get a different flange though....did you use a flux-wire(what i have) or gas shielded mig? I'm thinking a gas-shielded would be better because of the extreme conditions.
Registered User
Joined: Jan 2008
Posts: 7,547
Likes: 2
From: Quinton, New Jersey (middle of nowhere)
gas shielded mig FTW.
