Beating the Heat: Sealing the Firewall and Wrapping the Exhaust

One of the classic quirks of driving a kit car is dealing with cabin heat. After a few runs in the Stylus, it became very obvious that far too much engine heat was making its way directly into the driver's footwell.

Taking a closer look at the firewall revealed a design flaw. The original builder had placed the master cylinder and its attached fluid reservoir straight through the firewall, leaving a significant gap all the way around it. In fact, if you looked through the gap from the engine bay, you could clearly see the gold-coloured sound deadening on the inside of the footwell!

Because of the low pressure in the cabin and the high pressure in the engine bay while driving, this gap was essentially acting as a funnel, actively sucking hot air directly onto my legs.

To solve this, I had two options. The first was to completely redesign the entire pedal box and move the master cylinder away from the firewall area. However, that was a massive job that would involve replacing not just the brake pedal, but the accelerator and clutch as well, a rabbit hole I did not want to go down at this stage of the build.

The second, much more practical option was to fit a remote fluid reservoir. By moving the bulky reservoir up and out of the way, I was able to cut a neat plate that fits tightly around the master cylinder itself. This allowed me to completely seal up the gaping hole, getting rid of any gaps and stopping the hot air from being sucked into the cabin.

While I was in the engine bay trying to manage temperatures, I decided to tackle the biggest source of the problem. It is estimated that 50 to 70 percent of under-bonnet heat radiates directly from the exhaust manifold. Wrapping the manifold in heat wrap is a very quick and easy way to drastically reduce those ambient engine bay temperatures.

After finishing both of these jobs, I took the car out on the road, and it has made a massive difference to the comfort inside the car. The footwell is now isolated from that blast of engine air. The transmission tunnel still gets a bit warm, but that is a separate issue I will be tackling at a future stage!