The Yost Autosport BMW M4: Part 1 – The Foundation of a Proper Race Car


The guys at GenFab also went to work creating custom fender vents using the stock fender. What they ended up doing was completely shaping a smooth and super strong scoop behind the fender that directs air from the front wheel wells out through a simple, but large hole cut into the factory fender. The result was an efficient and clean design that can take a beating without becoming compromised.


Gutting the complicated stock wiring harness is a tedious process. There are more man hours into this part of the car than any other.
To say that the BMW M4 has a complicated electronics system is an understatement. All of the car's wiring and modules were laid out and meticulously labeled.

One of the most tedious tasks we took on with this build was the wiring. One of the things that always shocks me about modern cars in this day and age is the amount of electronics they have. When you have a super technologically advanced car like the M4 it gets even more complicated with electronically controlled DCT transmissions and electronic differentials. If time and money are of no object then a complete stand-alone wiring harness and ECU are the way to go but even that is iffy with a car as complicated as the M4. What we attempted instead was something that to our knowledge has never been done before and it’s something that will likely be an ongoing project on this race car for a long time coming and that is to gut the stock wiring harness. That doesn’t seem like an arduous task until you really start to learn just how complicated these cars are in the electronics department. Even things like deleting the radio turned out to be a complete nightmare as it is a major hub of communication in the car. With a collaborative effort between Yost Autosport, Gintani, and Southwest Bimmers there are more man hours into the wiring on this car than any other part of it so far. It is a painstaking process of deleting one unnecessary module at a time to determine what else that effects and if/how we can re-establish the functions lost. All of this is simply to save a few pounds of extra wiring and simplify the electrical system. That is the difference between a proper race car build and a track car.


A custom switch panel mounted just below the roof controls all of our auxiliary and aftermarket electronics. All of the labels light up and it also houses interior lights for use at night. The red box on top is a N.A.S.A. Pro Racing mandated safety strobe light only required during the 25 Hours of Thunderhill. If your car gets stranded on or off track at night, turn on the strobe so safety crews and other driver's can see you. These were mandated after a horrific incident at the 2014 25 Hours of Thunderhill where one driver didn't see a stranded car on track in the middle of the night until it was too late.

Aside from operation of the drivetrain and other factory electronics we also had to create a custom wiring harness for all of our auxiliary functions that we’re either adding or modifying from stock. As opposed to a traditional console mounted panel we went with a custom built switch box that mounts to the roll cage just above the rear view mirror. This moves everything up out of the way and makes for a really clean look. All the switches are easily accessible, easily operated, and the labels even light up so you can see what you’re doing at night. Everything connects to one simple Milspec plug on the back and runs to an independent fuse box we mounted in the trunk area of the car.

By now I am sure many of you are no longer interested in building your own proper race car from scratch and I can’t blame you, it is a ton of work, but if done properly the results speak for themselves. The Yost Autosport M4 will be an ongoing project probably for another year or two before we have truly reached the optimized potential of the M4 platform, but once we do it will truly be a factory-quality custom race car build that will be capable of truly amazing things. In the next article we’ll dig a little deeper into some of the fun stuff like power adders, the fuel system, cooling, and more!

For a little more background on Yost Autosport, check out our last build of our E92 M3 race car that we took to the 25 Hours of Thunderhill in 2014 & 2015!


And if you’re going to be at SEMA this year be sure to check out this M4 in person in the CSF Racing booth 3 in Central Hall!



General Fabrication


Fuel Safe

Yost Autosport

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