143: DIY Motorsport Isn’t Easy But It’s Insanely Rewarding

No matter the stage of a build, most projects reach a point where giving up feels tempting. They demand grit and perseverance—and Karel Silha from Karel S Motorsport’s wild DTM-inspired M4 Time Attack build is no exception.

We first spoke to Karel in 2022, and now he’s back to share what it really takes to shake down and test a home-built car of this caliber. Believe it or not, it all started with a toy car that Karel scanned and scaled up using CAD

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In this episode, we explore the engineering details behind the build. Karel explains the challenges of mounting a massive aero package capable of generating serious downforce. He highlights the practical difficulties of high-performance engineering in a garage environment.

Karel also shares how he’s utilised modern tools like CAD and FEA to optimise the design. We talk through his experience testing on KW Suspension’s seven-post rig—fine-tuning the suspension for low-speed mechanical grip and managing the immense downforce at high speeds.

We discuss the complexities of engine management with turbocharging and individual throttle bodies (ITBs), the importance of on track testing versus dyno calibration.

Despite the technical challenges and the emotional toll, this episode is far from bleak. Karel’s journey is incredibly inspiring and he’s optimistic that 2025 will finally be the year this insane build shows its true potential. 

Follow Karel here:

Instagram: karel_s_motorsport
Facebook: Karel S Motorsport
Youtube: karelsmotorsport

Links:

Episode 26 with Karel: Building a Tube Frame 1100hp Time Attack Weapon

Episode 75 with Dave Higgins (Aero Dave): The Realities of Driving and Maintaining Your Own F1 Car.

Timestamps:

0:00 DIY Motorsport Isn’t Easy But It’s Insanely Rewarding
4:12 Welcome back, can you give us a quick intro into who you are?
6:06 Can you give us a quick overview of the car?
12:24 Designing car modifications with serviceability in mind
16:40 What engine setup do you have in the car?
22:51 How do you go about the first shakedown for a car like this?
26:37 How did you go about fixing the initial issues?
30:12 What was going on with the wheel speed issue and why do we even need wheel speeds?
34:51 Why are you not running ABS?
38:15 Wheel speed issues wrapped up.
42:29 Were there any other issues in the initial testing? Dry sump issues?
49:40 Issues with the fixing points for the splitter and wing? 
53:27 What material are you using?
56:37 Can the average enthusiast get good results with FEA or do you need to be an Engineer to use it?
1:01:25 Did you have any cooling issues?
1:07:49 What is the height of the splitter at static ride height?
1:11:14 What is a 7 post rig?
1:19:44 Are you tuning the car onto bumpstomps to combat aero at high speeds?
1:21:46 Where does testing go from here?
127:11 How are you going about tuning your engine package? 
1:35:11 Were you able to do any gear shift calibration on the dyno? 
1:43:00 Will we see you at WTAK in Australia?
1:46:35 Final 3 questions