The Yost Autosport BMW M4: Part 1 – The Foundation of a Proper Race Car
Many of us out there, new or otherwise to our beloved car culture, don’t realize the difference between a track car and a race car and it has nothing to do with lap time. There are some incredibly fast track cars out there as we’ve seen in time attack, One Lap of America, etc. and truth be told most real race cars aren’t capable of putting down crazy fast lap times. What makes a proper race car is not horsepower or giant tires it’s all about optimization of a given platform the only limitations being budget and a rule book. A proper race car has thousands of man hours into it on things that you’ll never see unless pointed out. A proper race car is re-built and re-imagined from the ground up.
The Yost Autosport BMW M4 endurance race car wont be setting any time attack track records yet there’s more thought, money, and hours put into this build than we want to keep track of. It uses a stock S55 3.0L 6-cyl engine and stock twin turbos, a stock DCT dual-clutch transmission, and a tank full of 91 octane unleaded fuel. In fact, it uses as many stock parts as we can get away with not just for cost savings, but ease of replacement. Why? Because this race car is not built just for speed, it’s built for the long haul, and by long haul I mean North America’s longest endurance race…the 25 Hours of Thunderhill. Yes, 25 hours of constant racing utilizing the same car and four different drivers through day, dusk, night, dawn, and day again. The Yost Autosport BMW M4 race car competes in the top tier GT car class meaning the only rules revolve around safety equipment and the fact that the car has to be based off of a production model street car. Being that it is in the fastest GT car class it has to run a respectable lap time, but it has to be able to run that lap time 600+ laps in a row in order to win.
Completely dismantling a $60k+ car with before its first oil change is an unnatural feeling but it must be done in order to become a proper race car. Within 48 hours of bringing it home it was nothing but a bare chassis and a garage full of parts.Building a proper race car is no easy task, but building one for the 25 Hours of Thunderhill brings it to a whole other level. Really the only way to do it properly is to start from scratch and re-imagine and re-think every single piece and part of the car from the ground up. We picked up our 1500 mile old M4 on April 20, 2016 and before the engine could even cool down from the drive home from the dealership we had already begun tearing it down. Within 48 hours we had a completely bare chassis and a garage full of parts. Our deadline was SEMA, just six months later, but it didn’t just have to look the part, we had to have it done, and track-tested by then since there’s just three short weeks between SEMA and the 25 Hours of Thunderhill.
Six months may seem like adequate time to pull something like this off, but at this level of preparation it isn’t, and it certainly isn’t when your whole team consists of a volunteer crew with normal full time jobs. Since it was a “come over and work on the car when you have time” scenario it was rare that the entire team would be in the garage at the same time working on the car. When you work in conditions like that organization is key when tearing down the car. Every nut and bolt needs to be bagged and labeled as to where it came from. Every electrical connection needs to be marked before disconnecting. We had to have a crystal clear plan of attack. We couldn’t rely on memory for anything since the guy putting the bolt back in or re-connecting the electrical may not be the same guy who took it out.
Fabrication porn. Notching & welding and fancy name plates by General Fabrication in Las Vegas. There's a ton of thought and planning that goes into a proper roll cage, not just a rule book.Once tear down was complete the chassis went to General Fabrication, just down the road from our Las Vegas based shop for the next phase of the build…fabrication. Fabrication truly never ends but the major components like the roll cage, and preparation for the custom Fuel Safe fuel cell could be taken care of right away. Taking the chassis to a proper fabrication shop allowed us access to tools, people, and knowledge that would make things go a whole lot easier. Keeping things local also allowed us to work on other aspects of the chassis while GenFab was doing the roll cage.
Extra structural bracing linking the two rear strut towers and reinforcing the rear subframe helps tremendously with chassis rigidity. The rear subframe mounts are a known weak point on many M3/M4s. 
