Sharing the sport and the adventure

Finding Max-headroom in an E36 M3

I love my E36 M3, however being 6’3” tall I found the stock “vader” M3 sport seats lacking in multiple areas. They didn't provide much support, they didn’t contact my person in a convincing way, and most importantly when I squeezed into my Shoei, my helmet was in permanent contact with the headliner/sunroof/hard bits above me.

My initial effort was a pursuit of economy. I removed the driver’s seat and removed the bottom cushion. I then shaved about an inch from the bottom seat foam and re-installed the seat.

Let’s call this attempt the desperate-spend-no-money approach. What I found was that the headroom yield can be calculated as such (warning: geeky math joke ahead):

(total seat height + (total seat height - removed seat amount)) * 0

Basically removing a small amount of foam results in negligible benefit.


Step two was to spend some money, but not more than necessary. I looked for some good seats that appeared to be supportive, inexpensive, and have a very thin bottom cushion. My M3 is a semi-dedicated track car but I still want to maintain streetability. Therefore I wanted the seats to recline and slide, just like normal seats do. The seat the fit the bill was the Sparco R100. After finding the right seat I started looking at mounting options. Sparco makes a mounting bracket, but it appeared to be rather high off the floor which was exactly the opposite direction than I wanted. I did run across this nice mounting option from SafeRacer while I was checking out which gave me at least the option to be creative and find a low mounting point, which I did.

background

required parts

Tools:

6mm Allen

16mm socket

3” extension

3/8” ratchet handle

Dremel

Drill

~1/2” steel drill bit

~5/16” steel drill bit

Jigsaw or bandsaw

1/2” combination wrench


Parts:

Sparco R100 Seat

Sparco 00493 slider kit

Sparco 50001 hardware kit

Sparco 00491 generic base kit

1/8” x 1-1/4” x 36” steel stock

1/8” x 1-1/2” x 36” steel stock

Grade 8 bolt and matching locking nut

2 washers

E30 seatbelt receptacle

steps

The problem with the supply list is the depressing amount of kit you will actually use for this project. After taking everything out of its packaging, you will use the two side-rails from the generic base kit, about 4 washers, and two bolts. The rest can be put to another use (I used my spare parts to make a snow sled, but that would be another post).

The original mounting holes are 14 1/8” long. What I did next was to shape the side rails to this length. I started by enlarging one of the holes to fit the mounting bolt. I chewed through a few bits, so I cant say exactly what size I used but toward the end I was using a 1/2” bit I had in my toolbox. You might want to size up the bolt to a bit to find a more precise size to use. Once I had the “front” hole enlarged, I measured 14 1/8” back and drilled another hole. After I had both holes, I cut the corners of the bracket off with a jigsaw. The photo shows the before and after to get an idea how it should look.

The steel stock will serve as the horizontal supports for the seat. One (the wider of the two) will be bolted to the top of the two rails in the front, while the other narrower piece will be underneath the rear of the rails. This is where the magic happens. Since the rear plate is on the bottom, a few benefits arise. The first is the notion that the rear of the seat will be at its absolute lowest (on the floor itself). The second is that the difference in height between the front and back will give the slanted seat feel that provides comfort and thigh support. The third is the slanted seat will move the seat position higher when moved forward, resulting in a higher seating position for the less-tall people in the family. Lastly, the rear support will be connected to the car using the factory mounting holes and bolts. Because of this, we will mount the seatbelt to this rear steel support.

I measured the factory seat width to be 17 3/4” wide. The Sparco bolt width is 13 5/8”. Therefore the Sparco will sit inside the factory holes, and you will want to push the seat as far toward the center console as possible. I drilled the mounting holes and lined up the seat with its slider attached, and then pushed the seat slider up against the inside rail, then marked the mounting hole with a marker. Even with the new seat pushed as far as possible toward the centerline of the car, the center of the new seat will be about 2” off of the center of the steering wheel. Once installed I don’t notice the difference.

These pictures should give you an idea on what the rear bracket will look like once completed. Its important to note to bend the seatbelt bracket away slightly from vertical, the slightly-bent look in the photos was not by accident.

As a side note, use a real nut on the grade-8 bolt. I used a metal locking nut when complete, this photo was taken during mockup. Even with the tab slightly tilted, you will also want to place the head of the bolt toward the seat, unlike the photo.

This photo shows why I am stressing the bolt and its placement.

Once you bolt in the final product, the only thing left to do is sit back and enjoy the added headroom and incredible support!

The front mount is secured to the rails using two bolts, and the square-nut that comes with the kit. It is adjustable so its best to keep it loose until the rear of the seat is secured, since the rear holes are drilled and fixed in position. As can be seen in this photo, the seat mounting points are as low as they can go. Potential legroom also improves dramatically.

The final brackets will look like this (after painting)

In order to provide clearance toward the inside of the seat, the rail will need to be notched as seen in the photo to the right. About 2” is removed from the inner rail toward the top, and then smoothed.

I have not addressed the last component in the conversion because I have not addressed it in my M3 yet. I found it necessary to remove the factory E36 seatbelt receptacles because they would not fit with the new seat in place (I tried). By using the E30 receptacles the seat belt will fit and the seat belts will slot properly into the receptacles, but the SRS light will be illuminated on the dash. To fix this, I will need to defeat the seatbelt switch circuit. In preparation I placed the E30 receptacle with the wire on the passenger side. My plan is to bypass both seatbelt circuits by using a resistor, and then wire the passenger seatbelt circuit to mimic the passenger occupancy sensor. The reason I have not done this yet is because I foolishly sold my vaders before finishing the project, and therefore do not know what the resistances should be. I will be visiting an E36 soon with my multimeter to find out though, and will update this page when I have the last detail.