Before and After Turbo Blanket Test on a 550BHP RS4

If you have a high-powered car like Alex's 550bhp Audi RS4, you know that heat in the engine bay is a problem.

After tuning his RS4 for more boost and power, he found himself opening the bonnet to what felt like an oven, and the Intake air temperatures were in the high 40 degrees.

The engine bay heat was intense, to the point that touching the plastic engine cover could nearly burn your hand. This level of heat isn’t just uncomfortable; it can wreak havoc on nearby components and sap performance through heat soak.

I’m Matt, owner of Exoracing. Since 2018, I’ve been building and testing performance cars and helping thousands of customers tackle heat issues.

From turbo Honda Civics to track-built monsters, we’ve seen what actually works to keep engine bay temps under control, and what doesn’t.

We specialise in heat management solutions, and we decided to put one of our favourite products to the test on Alex from HPWorx's newest purchase, the 2022 Audi RS4.

If you would prefer to watch the video of our testing, then click the video below, and if you could subscribe whilst you're there, that will help us to be able to make more videos and articles like this in the future.

By the end of this article, you’ll see exactly how our Exoracing turbo blankets can tame engine bay temperatures, protect critical parts, and even help your car run more efficiently.

We’ll show you the proof using our thermal imaging camera, with real before-and-after data from his RS4, and the intake air temperature data logs he sent us at the end of the day.

First, we’ll outline the heat problem we faced, then walk you through installing the turbo blanket, and finally dive into the results. Spoiler alert: the temperature drops we recorded were dramatic!

Here’s the game plan moving forward:

• We measured baseline engine bay heat levels on the RS4 (no turbo blanket).
• We install an Exoracing turbo blanket on the RS4’s turbochargers.
• We run the same test again to record the post-install temperatures.
• We compare the data side by side and conclude how effective this simple mod really is.

(This guide is brought to you by Exoracing — UK specialists in heat management and performance parts.)

Baseline Heat Levels (Without a Turbo Blanket)

Before fitting the turbo blanket, we wanted to understand just how hot things were getting under the RS4’s bonnet. The Audi RS4 uses a “hot V” engine layout, which is where the twin turbos sit right in the valley of the 2.9L V6, essentially on top of the engine.

This design makes for great performance and compact packaging, but it also means a ton of heat is concentrated in the centre of the engine bay, directly beneath the bonnet. With the car pushed to 550bhp (with the factory power being 450bhp), that heat only intensified.

To establish a baseline, we took the RS4 for a spirited drive and then quickly lifted the bonnet for measurements. Using our thermal imaging camera, we checked the temperature on several key points:

Plastic engine cover:

This is the large plastic cover sitting atop the engine. It’s not directly touching the turbos, but it’s one of the first things you feel when you open the hood. After our drive, the surface of the plastic cover read 45.1°C at the central point.

That’s extremely hot for a component you can normally touch, hot enough that prolonged exposure could start to make the plastic brittle or discolour.

Aluminium heat shield:

The Audi RS4 has an aluminium heat shield plate over the turbo area, which is part of the factory heat management. We measured this shield at roughly 26.4°C.

The metal shield was doing its best to protect the bonnet and surrounding components, and was doing an ok job, but it could always be better.

Turbocharger exhaust housings (hot side):

Unsurprisingly, the turbo’s exhaust housing was the hottest spot. The exposed turbo housing hit about 117.8°C on our IR gun, which is above the boiling point of water.

You might be asking why this is ONLY 117.8°C, as that is very low for a car with sort of power and boost. Well, in the video, you can see that from the factory, Audi includes shields over the exhaust housings, as otherwise this would be around 5 x hotter than this without it, and would melt everything. Due to the design of the turbo and downpipes, they have to do this, or the paint on the bonnet would disintegrate.

This heat was radiating out to everything nearby, including hoses, wiring looms, and the underside of the bonnet. You name it, they were all soaking up that heat.

It was clear from our baseline test that engine bay temperatures were out of control after a hard run (and we only went out for around 8-10 minutes per run). The hottest part of the bay was dumping heat into everything around it.

No wonder Alex's intake air temperatures were creeping up, and the engine bay felt like a sauna. We needed a solution to keep that heat where it belongs (inside the turbo and exhaust), instead of letting it spill into the rest of the bay.

Installing the Turbo Blanket

With our baseline numbers recorded, it was now time to install the turbo blanket. We used 2 x Exoracing Turbo Blankets designed for turbo exhaust housings with a working temperature around 1200°C.

It’s a thick, insulated jacket made of layers of heat-resistant fabric (fibreglass and volcanic rock weave on the outside, with a high-temperature silica insulation inside).

Essentially, a turbo blanket wraps around the turbo’s hot-side housing to contain the heat. Instead of that heat radiating freely into the engine bay, the blanket keeps it trapped inside the turbo housing and exhaust, where it can do its job (spooling the turbo) without cooking everything around it.

To see how good these blankets are in terms of materials, make sure to watch our testing video, where we nuked the turbo blanket with a propane torch for extended periods and got data from the inside and outside with our thermal imaging camera.

For the Audi RS4’s twin-turbo setup, we had to fit two blankets (one on each turbocharger).

The RS4’s turbos are nestled in the engine’s “hot V”, which is a tight space to work in. We waited until the car had fully cooled down (never try to install a turbo blanket on a hot turbo – you will burn yourself, and the blanket won’t seat properly on a hot surface). Working carefully, we accessed each turbo from the top of the engine bay.

The process was as follows:

• Remove or loosen any covers/obstacles: We took off the plastic engine cover and aluminium cover to get better access to the turbo housings. In the RS4, space is limited, so a bit of patience is needed here to remove them.
• Position the turbo blanket: We slid the turbo blanket over the hot side of the turbo. The blanket is designed like a shell that encapsulates the turbine housing. We made sure it covered as much of the metal surface as possible, while keeping clear of any moving parts (like the wastegate actuator arm) and oil or coolant lines. Sometimes the actuator arm is a problem, and you don't want this to stick or get caught, so just be careful here.
• Secure the blanket: The Exoracing blanket comes with built-in fasteners (springs and hooks made of stainless steel). We hooked the springs through the grommets on the blanket and pulled them tight to lock the blanket in place around the turbo. This step is a bit fiddly on the RS4 due to limited space. Alex actually used a bit of welding wire, which came in handy to pull the springs into place.
• Double-check clearance: After installation, we double-checked that nothing was touching or rubbing against the blanket that shouldn’t be. On the RS4, the blanket sat snugly around each turbo, and we verified there was clearance from wiring and the underside of the bonnet.

  The last thing you want is the blanket touching a plastic part and melting it. Though these blankets usually have an outer layer that’s safe to contact most surfaces, it’s good practice to ensure an air gap if possible.

The installation and heat management test took roughly 20 minutes for both turbos, mainly because of the RS4’s tight engine layout. If you’re doing this yourself, allow plenty of time and make sure the engine is cold. Alex found this out the hard way, don't be like Alex, haha!

Once the turbo blankets were on and secure, we reinstalled the engine cover and any bits we moved. Now it was the moment of truth time, we were eager to see how much difference these little insulated blankets would make.

Post-Install Results

With the turbo blankets installed, we took the RS4 out for another hard run to get the engine and turbos nice and hot. Same driving routine, same ambient conditions, we wanted an apples-to-apples comparison with our baseline.

After the run, we popped the bonnet and got the Infrared thermometer ready to measure those same key points as before. The difference was immediately noticeable, even before measuring; we didn’t feel nearly as much radiant heat washing over us when the bonnet was opened.

Now, let’s look at the numbers:

Plastic engine cover:

Previously, this hit 45.1°C. After the turbo blankets were fitted, the plastic cover temperature dropped to around 25.5°C. That’s about a 19.6°C reduction!

In practical terms, the cover was warm to the touch, but no longer hot. This is a huge improvement; it means the blankets prevented a lot of heat from soaking upward into the intake manifold area and the cover.

Aluminium heat shield:

This metal shield, which was 26.4°C before, was now reading about 10.5°C. A 15.9°C drop.

The shield was warm, but not untouchable like before. This indicates that far less heat was reaching the shield from the turbo area, thanks to most of it being contained by the blanket. The underside of the bonnet above this area also felt cooler than before, which is great news for the paint and any insulation, and less risk of heat damage over time.

Turbocharger housing (outside of the blanket):

This is where we expected the biggest change.

Our baseline was 117.8°C on the turbo’s surface (even with factory heat management. After installing the blanket, measuring the outside of the blanket on the turbo, we got it down to 70.0°C. That’s a massive 47.8°C drop in the surface temperature!

Essentially, the turbo blanket was holding in a huge amount of heat that used to radiate into the engine bay. Now, the turbo itself internally is still just as hot (if not even a bit hotter internally, as the heat is kept in), but externally, a lot less of that heat is escaping.

It’s worth noting that keeping more heat inside the turbo has a couple of side benefits: the turbo can spool slightly faster (hot exhaust gases flow faster), and the catalytic converters/downpipes get hotter quicker, which can improve efficiency.

But the main benefit we were after was lower engine bay and intake temperatures, and that’s exactly what we achieved.

After the blanket install, other components around the engine bay were also cooler to the touch.

For example, the intake pipes and airbox on our RS4 felt cooler, meaning less heat soaks into the intake charge.

Alex was data logging the IAT's as we were driving and kindly overlayed them for us when he got home, and we saw a drop in intake air temperatures throughout the entire rev range.

The biggest drop we saw was around 10°C, with an average of 7°C. This dropped him from the high 40°C mark to the low 40°C mark, which is a massive drop.

Bearing in mind that all we did was install turbo blankets, we could easily drop that even further with more heat management, extra airflow, etc. This just shows how powerful heat management is in terms of performance, knock and all the other detrimental parts of excessive heat.

In a turbo car, every degree of cooler intake air helps maintain power and prevent knock.

Overall, the post-install results confirmed our expectations: the turbo blankets made a dramatic difference.

To make it crystal clear, we’ve summarised the before-and-after measurements in the table below.

Real Results: Before vs After Data

Numbers speak louder than words.

Here’s a direct comparison of the temperature readings we took before (no turbo blankets) and after installing the turbo blankets on Alex's 550bhp Audi RS4.

These were measured immediately after a hard run, using the same IR thermometer and under similar conditions:

As you can see, the turbo blanket had a significant impact on every measured point in the engine bay by between 40% and 60%. The plastic cover and heat shield saw drops of 15.9-19.6°C, which is substantial.

That kind of reduction can mean the difference between plastic components slowly baking over time versus staying within a safe temperature range.

The turbo housing’s external temperature plummeted by 47.8°C, highlighting just how effective the blanket is at containing heat at the source.

It’s impressive to see something so simple like this making such a big difference. By containing the heat within the turbo, we’re not only protecting nearby components but also keeping the ambient engine bay temperature lower (around 10°C colder at max!)

A cooler engine bay can improve overall reliability: wiring looms won’t become brittle as fast, rubber hoses won’t crack as soon, and critical sensors will be less likely to suffer heat-related failures.

Plus, when you finish a drive, the engine bay will cool down faster without all that retained heat soaking everything.

In this case, the Audi RS4’s intake system will also benefit from these lower temperatures. A cooler engine bay air means the intercoolers and intake will be taking in cooler air than before, which helps maintain power in back-to-back pulls.

Overall, the data proves that our turbo blanket test was a success. If you’re pushing a high-performance turbo car on the road or track, a turbo blanket is a highly effective tool for thermal management.

The most insane thing about this test is that because the turbos were mashed under the heat shield, we couldn't take advantage of air flow and heat dissipation, so if anything, this test was more worst case scenario than it was a best-performing version of the blanket.

If we had a totally open engine bay with lots of room, we would have reduced these temperatures even further, just by having space around the hot parts and access to more airflow.

Conclusion

Managing engine bay heat doesn’t have to be complicated.

This simple test that took us around 20 minutes on the 550bhp Audi RS4 shows that just one upgrade, a quality turbo blanket, can dramatically lower under-bonnet temperatures.

By containing heat at its source, we protected our plastic engine cover, wiring, and other components from getting fried. Not only does this improve reliability (no one likes replacing brittle wires or melted plastic bits), but it can also help your car perform more consistently by keeping intake temps in check.

If you’re pushing a turbocharged car hard, whether on the street or track, investing in heat management is a no-brainer and will save you money in the long term.

We were genuinely impressed by how much difference a turbo blanket made in Alex's build. It’s a relatively inexpensive upgrade that delivers real, measurable results.

The RS4 is now a bit cooler, happier, and more durable, and we have the data to prove it.

Related Products & Links

• Exhaust Wraps: Wrap your exhaust manifold and downpipe to further reduce engine bay heat.
• Reflective Tape & Sleeving: Shield wiring and hoses from radiant heat with adhesive gold reflective tape and high-temp sleeves.
• Turbo Blankets & Heat Shields: Explore turbo blankets (like the one used in this test) and bolt-on heat shields for various turbo models.
• Related Blog: What Is a Turbo Blanket? A deep dive into how turbo blankets work and their benefits for any turbocharged setup.
• Related Blog:7 Engine Bay Heat Problems With Simple Solutions. Common engine bay heat issues and how to fix them (includes tips on blankets, wraps, and more).

About the Author

I’m Matt, the owner of Exoracing Ltd, a UK-based performance parts brand specialising in heat management and performance upgrades.

Since 2018, we’ve helped thousands of car enthusiasts and workshops reduce engine bay temperatures with tested, proven products, all backed by first-hand experience from our own builds and our customers’ projects.

Got questions about your setup or need advice on taming under-bonnet heat?

Feel free to message us on Instagram @exoracinguk or hit the Contact button on our website.

We love hearing about your builds and helping you find the right solutions to keep them running cool and strong.

Enjoyed the article or have insights to share? We would love to hear from you!