Most people fitting or upgrading a turbo like to have it on display… immediately visible once you lift the bonnet. But there can be problems in taking this approach – and the biggest is heat. The exhaust manifold, exhaust housing and first section of exhaust pipe are likely to get very hot when the turbo is working hard – hot enough in fact to glow red.
That heat increases general underbonnet temperatures – not good for keeping your intake air cool. It can also cause the failure of nearby components like alternators, and in extreme cases can cause bonnet paint to blister. The danger of glowing turbos near oil filters and brake lines should also be obvious…
So how can you reduce the heat emitted by a turbo? The answer is to use heat shielding.
Heat shielding is effective because most of the heat coming off the turbo is radiant energy – the sort of heat you can feel when you place your hand near an electric radiator. A barrier placed between the radiant heat source and whatever you’re trying to protect will stop this heat transfer. Of course, you don’t then want the barrier itself to get really hot, or it will become the new source of radiant heat!
So what’s needed is a barrier that will cope with being near a glowing exhaust turbine, and will then transmit little of that heat through the barrier itself.
Heatshields with these characteristics are now widely available. They typically comprise a plated thin gauge steel sandwich, with a heat insulating material placed in the middle of the sandwich. The metal sheets are heavily embossed which keeps the sandwich together, even when the sheet is cut.
The sheets are purchased flat – but most often you don’t require a flat heat shield! So how can you shape what you need?
When buying turbo heatshield material, be wary of people selling general-purpose underbonnet insulation as if it is proper heatshield material.
Underbonnet insulation may have a thermal barrier (eg aluminium foil) but it is not designed to be near red-hot glowing metal bits!
Look for material designed for use specifically for use as turbo or exhaust heatshields.
Working with the material
While at first it appears that the heatshield material will be hard to work with, once you get the hang of it, you can shape the sheet quite well.
Gentle curves can be formed by placing the sheet over a pipe and then pushing it downwards to conform to the curve, while tighter bends can be formed by lightly using a hammer and wrapping the material around the edge of a bench or similar.
A hammer and a dolly can be used where the edge needs to follow a curve.
Cutting of the material can be easily done with tinsnips, or a 1mm cutting wheel in an angle grinder can be used (be careful to wear a mask). The edges can be sanded or gently filed.
A turbo heat shield works best if there is an air gap between the heat shield and the turbo (or between the heat shield and the exhaust pipe or manifold). In other words, the shield should be designed so that it is preferably not touching the turbo.
Keeping the shield a fixed distance from the turbo requires that it be shaped so that it has intrinsic stiffness, and/or it uses lots of brackets to hold it in place.
Also be careful that the heatshield cannot foul the wastegate actuator!
The heatshield material can be joined using nuts and bolts, or as shown here, with pop rivets. Don’t place the rivet straight through the thin-gauge material – it will pull through. Instead use a large diameter washer under the head of the rivet to spread the load. Not also that the dimpled heat shield material should by flattened before the rivet is inserted. If you don’t first flatten the material, the rivet cannot pull up tight. This flattening is easily achieved by placing the sheet on a firm surface and then judiciously using a hammer.
The rivets shown in the above pic attach to small angle brackets placed on the other side of the sheet.
Here the sheet has been stiffened by the use of rolled edges top and bottom. These were formed in a two-stage process: first the edge was partly folded with angled long nose pliers, then a hammer and curved mandrel was used to give the full 90 degree bend.
Whatever design you develop, remember that the heatshield needs to be able to placed into position (and taken off) with the turbo in situ! In this case, that required making the heat shield in two pieces. The larger of the two is ‘opened out’ to fit around the exhaust housing – there needs to enough flexibility in the shield design to allow this to occur. With the larger piece in place, the smaller piece can then be inserted.
To hold the heatshield securely in place, this steel bracket was made. It bolts to the exhaust pipe flange and provides three mounting points (the lower one not visible here) for the heatshield. Rivnuts (arrowed) were used to facilitate the mounting – there’s therefore no need to access the nuts when screwing the heatshield into place.
The completed heat shield. I chose to go over the top of the wastegate actuator rod – there was plenty of room and it created a bigger air gap. However, the heat shield more closely follows the shape of the lower part of the exhaust housing – here there was less room available.
The turbo in place. The heatshield was built mainly to protect the alternator (arrowed). The shield also protects the ignition coils, steering tie rod and firewall from excessive heat. The bare exhaust pipe will later be covered in exhaust wrap.
The heatshield design that you come up with is largely dependent on your time and patience. Take it slowly, remember that the material is pliable enough that you can undo bending mistakes, and measure twice and cut once!