4" downpipe design concern

[Bob Beauchaine]

I would be interested if the down pipe had 45 degree angles in place of the 90's. I've also got a BD exhaust brake that would require a setback. Down pipes off 2nd Gen trucks are perfect model for my down pipe. I realize that this is a lot to ask but if I'm going to switch to 4" I am looking for optimum flow. To me it's all about efficiency.

Bob

 

[MMiller]

Hey Mark, I myself would be interested, if a 4 inch down pipe would be made. There are several companies that make 4" exhaust from the downpipe back, but I want a 4" downpipe also. Please let us know!!



Michael Miller

 

[nascar mark]

Originally posted by Bob Beauchaine

I would be interested if the down pipe had 45 degree angles in place of the 90's. I've also got a BD exhaust brake that would require a setback. Down pipes off 2nd Gen trucks are perfect model for my down pipe. I realize that this is a lot to ask but if I'm going to switch to 4" I am looking for optimum flow. To me it's all about efficiency.

Bob

Hi Bob,

Yes, it will be 45 deg angles.

 

[Bob Beauchaine]

Hi Mark

If it will work with my BD exhaust brake I'm in for one.



I've taken the next "efficiency" step - we will see how it works. I would like to get an injector somewhere between the PW's and the POD's. Maybe some honed PW's. I need to give Piers a call and get his take on my set up. I'm looking for HP in the 275 range - I don't think that is too far off where I am now.

Bob

 

[jlast]

Banjo



I just made a exhaust flange and adapter to 3. 5" tubing. I took an 1/8" in plate cut it down to outside flange circle then cut a 2. 5 in hole in the center, also angled the outside edge to work with the sealing band. Took 3 in tubing not sure on the thickness about 3/4 in wide, and banded it on the back of an extra housing I had and end up with about an 1/8 on the inside of the pipe to weld onto the 1/8" flat flange. The orginal flange band did just barely touch the 3" pipe but not enough to affect the sealing. Then used and adapter to go to 3. 5" pipe the total distance from the flat flange to 3. 5" is around 1 3/4" and could have been shorter with use of 1/2 or 3/8 inch wide piece of 3" pipe. This is done with the factory 1st gen flange not the 45 elbow for a 2nd, and was done in steel not SS, and for use of a h1c or hx35w.



I wanted short as possible to be able to use the longer wastegated housing with 90's in the downpipe, but with all the talk of using 45's I am going to take a look and see if I can make them work without a 2nd gen 45 housing. I like the free flowing exhaust idea, my made pipe, from downpipe back has 9 less then 45 degree bends in it and exists behind the rear wheels, now see if I can do the downpipe in three bends or less.



Jlast

 

[skobylenski]

I just started thinking about this again, considering I'm thinking of adding stacks next summer. Did anything come of the R&D for these 4" downpipes?



Scott

 

[Bob Beauchaine]

Rip Rook installed a 4" system in my '93. It is 4" from the turbo on back and is similar to a 2nd gen. down pipe. The top 45 is formed by my exhaust brake and there is a bottom 45 that leads on back through a full 4" system. There is some harmonic noise at 60 mph but since I rarely run at that speed it's not a problem. I feel that my truck breathes very well. That coupled with my open breathing system, Old Smokys fuel pin and some other tweaks and the truck can really move.



Bob

 

[backroad]

Hey Bob, How did you get the 4" size on the back of the turbo. I just built my mufflerless 4" system, but it's still 3" off the turbo and through the first 90 bend.

 

[Bob Beauchaine]

My exhaust brake is 3" and bolts up to the turbo. The down pipe immediately goes to 4" at that point. With this setup it breaths much better than the old 3. 5" system.



Bob

 

[cguthrie]

Hey Mark i would be interested in buying one. Have you heard about how much they will be yet?



Chris

 

[nascar mark]

I have sold 7-8 4" downpipes for first gens so far. The 1st one I made was for my truck and then I started selling them for PDR about 4 months later because of the requests of fellow 1st genners wanting a 4" exhaust system.

I had to try and remember how much angle and length without pulling mine out of the truck. 1st one I sold came back for a little tweeking (I also managed to make a jig) and I haven't had any problems since.



It is a real tight fit but it works. The downpipe is a TRUE 4" (no 3" in the pipe at all) with gentle bends. I had a machine shop make 3"-4" adapters, so the adapter fits between the 3" exhaust housing of the turbo and the 4" down pipe. You need a 4" V clamp to put it all together.



The downpipe is $180us

The adapter is $49us

The 4" V clamp is $25us

 

[Bob Beauchaine]

Mark

What did you do about the transmission dip stick? I've got someone with a '93 and an automatic transmission - the way I see it when I compare mine with his, the down pipe would go right through the dip stick tube. He would like a 4" system but not with 3' of 3" down pipe.



Bob

 

[nascar mark]

The dipstick has to be bent and re-posistioned or buy a 2nd gen dipstick as it will work.



Mark

PDR

 

[y-knot]

I think you guys should look up HOG PERFORMANCE, they build a very nice stainless steel system, and there 4" down pipe starts right at the turbo. None of this after the bend, change size junk. They cone out the transision right after the flange, and it takes about 4-5" to finish, very smooth, and beautifull weld job, looks like it should.