Garagistic M6X Swap Guide- Exhaust

The exhaust will take on a different format, divergent to the typical Minimum, Extra Mile, and CRAZY format. This will be a straightforward, very direct approach to installing the exhaust in the cheapest possible manner.

Cost of the exhaust at a minimum (with maximum fabrication and DIY) is: 10hrs & $750. If this part of the swap is done right, it can sound amazing. The $750 figure includes the Garagistic Headers as shown in section 18.4. Check Garagistic’s website for the latest pricing.

You can use stock headers; either the 2 to 1 doubles or you can use the 4 to 1. Both can work, but the amount of effort necessary or the availability drives one option over the other. You can always build your own, but I tend to gravitate to the tried and true methods and attempt to improve upon them. I suggest bringing it down to an X-Pipe for smooth operation and a nice throaty sound. Then each pipe should have a resonator to quiet it down a bit. Then keep the dual pipes out to a 2 in, 2 out muffler. Allow me to elaborate. 

Here is my materials list that I used for my exhaust. I used the following setup:

Table 11

Exhaust Part Description Jegs,Summit/P/N QTY
Exhaust Tubing 2.25" aluminized tubing - 4' length 555-30609   4
V Clamps 2.25" with collars - Mild Steel Ebay 2
X-Pipe 2.25" Narrow 555-30680 1
Resonators 2.25" inlet/outlet AR43514B 2
Mandrel Bend 2.25" Mandrel 555-319235 1
Mandrel Bend 2.25" Mandrel 555-319335 1
Muffler Flowmaster Series 50 Dual 2.25" 524554 Series 50 SUV 1
Wrap & SS Clamps Jegs 2" black tape -  15' 555-32055 1
Stainless Steel Clamps SS Clamps 8" 6/pkg 555-10625 1
Heat Shielding Jegs heat shield 1.5"Wx20' Roll 555-32030 1
Muffler Tips 2.25" tips - Haven't picked yet Various 2


Headers can be done 1 of 3 possible ways.

1. Source exhaust manifolds I like to call “2 to 1)”.

These can be sourced from the following vehicles (see Figure 67):

a. E31 840i/840Ci

b. E32 740i/iL

c. E34 530i/540i

d. E39 540i (before 1999)

2. Source exhaust manifolds I like to call “4 to 1”.

These can be sourced from the following vehicles (see Figure 68):

a. Without Cat

i. E53 X5 (without Cat)

b. With Cat

i. E38 740i/L

ii. E39 540i (after 1999)

These “4 to 1” headers, while available on ebay or other consortiums, still require a significant amount of rework in order to clear the driver side steering column and the passenger and driver side footwells.

Fortunately, Garagistic sells these “4 into 1” headers that are already modified for this specific swap. These headers already have 2 hole flanges welded on to the headers. This makes the headers aspect of the swap, which is one of the most difficult parts, a breeze. That way, you can focus on the rest of the swap! See Figure 69.

I used the 4 to 1 setup from a (E39) 1999 540i. Mine came with the catalytic converters, but do not fit in the E30 since it hits the passenger and driver foot well, not to mention the steering column. So after removing the cats and discarding them (they are not worth much at all), I started welding and cutting to adapt to the exhaust size I planned to utilize. See Figure 71, which shows the exhaust headers put into place. I had to cut pretty high up on the headers and weld new piping.

After cutting them down to the correct length, I then attempted to weld the double wall together. Then I welded a 2.5” exhaust tube to start the downpipe. See Figure 70 which shows me welding the double walled header.


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Figure 70 Double-Walled Header

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Figure 71 Passenger & Driver Side Exhaust Mocked Up

As you can see in Figure 72, I welded the 2.5” tubing to the welded double wall. It was a very iterative process of measure, cut, tack, weld…. Over and over to get the shape of the tubing correct.  

As shown in Figure 73, note that I then welded the 2.5” to 2.25” reducers off of the elbows. I wanted the entire exhaust to be 2.25” from the headers to the muffler. So with that being said, I bought 2 2.25” V-Clamp assemblies. I bought these in an effort to easily and effortlessly remove/install the exhaust as I needed to.

We all know that with all of the installation/removal of exhaust, it is really a pain sometimes. I decided to go this route to make it easier on myself.

18.5 X-PIPE
I used a typical mild steel X-Pipe. Not an H-Pipe. The X-Pipe works much better with the M60 engine since the M60 is a much smoother running & higher revving engine than a Chevy 350 for example. X-Pipes will give the engine a nice throaty sound while enhancing flow and efficiency. See my downpipes and x-pipe as shown in Figure 74. See the part number in Table 11.

Welding the X-pipe was difficult due to the variation of welding and the warping of the steel during tacking/welding. This is how I installed the X-Pipe:

I hung the X-Pipe roughly where I wanted it to be installed as shown in Figure 77. Hanging it with zip ties was sufficient.

From then, I started mig-tacking the passenger side downpipe to the V clamp output and then to the passenger inlet of the X-Pipe. Small Weld Tacks are key here. Then I did the driver side. Once I thought it was sufficiently tacked (5-6 tacks each pipe), I removed the V-Clamps and took the entire V-Clamp, downpipe, X-Pipe subassembly to be welded.

I proceeded to weld the entire assembly up as shown in Figure 74. When I attempted to reinstall the subassembly to the downpipes, I discovered that the 2 V-Clamps were way off. I deduced that it was primarily the warpage of the tubing during final weld that caused the downpipes from diverting so far from their original position.

I then had to cut/weld/cut/weld/cut/weld. It was a very iterative, cumbersome, frustrating process, but I finally finished and it matched up nicely.

I decided to go with a 2.25” in/out muffler. It worked very well with my needs for this project. I used for a lot of comparisons on how a muffler will sound. It has a nice raspy, throaty sound, but is quiet when you are not heavy on the pedal. Maybe I got lucky, or the research I did paid off, because when I first started it up, it sounded great! See my muffler depicted as shown in Figure 53. See the part number in Table 6.

I hung up the system by 2 mounting points. The first one being the stock exhaust hanger (1 strap) and rubber mount associated with it. The Magnaflow muffler was slightly smaller than the stock 325i muffler, so I had to shorten the metal straps for ease of installation. For some more detail, see Figure 79.

The second mounting location was picked to be at the stock exhaust pipe location on the rear subframe. I welded a triangular steel piece and drilled a hole in the center. I used rubber double shielded “washer” that was originally used for the E30 condenser fan mounting hardware. I took that and then screwed it right into the subframe stock bolt location. It allows a nice stiff mounting fixture while allowing for some play for engine roll during hard acceleration. See Figure 80 for some more information. This is a relatively rigid installation and in the near future I plan to update this to what was originally designed.

You can paint the exhaust with special high temp exhaust paint. This can be found at any Autozone, Pep Boys…etc. I used 2 cans. One was a primer and the other was a black paint. One can is sufficient to cover the entire twin exhaust system. It is important to paint the exhaust for one major reason. RUST. Unless you are using expensive stainless steel tubing, which is not prone to rust, it is HIGHLY advised to paint it prior to final installation. It helps to protect not just the tubing, but more importantly the welds. The welds happen to rust exponentially faster than the tubing itself. Here are 2 pictures in Figure 81 & Figure 82 of the final painted exhaust.

The final fitment of the exhaust in the E30 is shown below in Figure 83.  It was not difficult at all, but rewarding.