Nerd-O-Scope: APR 2.5 TFSI Stage III GTX Turbocharger System

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So there’s the ‘how’ the design work of the kit was done. But the ‘how’ is not what makes this kit special, it’s all the smaller details which make up the ‘whys’. APR has gone the extra step in nearly every facet to make this kit perform well and be reliable. The key word is reliable. It’s quite easy to put a kit together that will put down good dyno numbers, but it’s an entirely different matter to make it reliable for hours of straight road course track abuse and last the better part of 100K miles. Two of the biggest factors in making a turbo kit reliable are material selection and heat management.

 

The exhaust manifold APR developed stands apart from anything else I’ve seen for the reasons of material selection and heat management. In the hierarchy of common materials used in turbo systems, regular grey iron is the absolute bottom most junk. Next up, you get higher grades of iron like hi-silmoly which is commonly used in lower temperature EGT diesel applications. Then you get to ni-resist used in gasoline and very highly stressed diesels running higher EGTs. Stainless steel is the big jump used for very high performance gasoline applications running very high EGTs. And then the big jump from stainless steel is Inconel. Stuff like turbine wheels in turbochargers and turbine blades in jet engines are made of Inconel. APR investment cast the manifold from Inconel. This is badass on two levels.

Being that the manifold is cast, it is inherently more reliable than a welded and fabricated manifold as the weld joints can make the materials weaker. It’s all due to the HAZ (heat affected zone) when welding. There is a reason all those fabricated manifolds tend to crack at the welds. It is certainly possible to make a reliable welded manifold and it is certainly possible for cast manifolds to crack if not designed properly to handle thermal stress, but a cast manifold is inherently more reliable due to the lack of the weld joints. Why do the vast majority of aftermarket turbo kits come with fabricated manifolds? Because the tooling to cast a manifold is not cheap, not to mention all the design tools required such as 3D modelling and smaller companies just can’t afford it. Again, APR shows it is able to shell out the big bucks up front in order to deliver a superior product.

The other extra step APR has taken with the exhaust manifold is to have it coated with Swaintech White Lightening Thermal Barrier coating. The coating his two major benefits by keeping the heat in the manifold: less heat is rejected to the surrounding stuff around the manifold and heat is energy which improves turbo performance. Back on my good ole Nissan SE-R, I also had my manifold coated by Swaintech and I attribute that to making my rubber water lines last five years instead of two. There is a lot of rubber and plastic stuff in a modern engine bay which don’t react well to getting baked, so keeping the heat in the manifold is a good thing when it comes to long term reliability. Anyone who has dealt with old vacuum lines on a Z32 300zx twin turbo knows how heat can bake the lines. In helping my buddy pull the engine from his Z, the vacuum lines snapped like dry twigs as the heat over time had made them very dry and brittle.

 

Providing the boost is a Garrett GTX3576R turbocharger. This is my go to recommendation turbo for any gasoline engine in the 2-3.5 liter displacement range looking for 600whp. As the 5-cylinder in the TT RS is 2.5L, the turbo works quite well in this application.

On the hot side of the turbo is a Tial V-band stainless steel 0.63 A/R turbine housing. Why V-band? Well, going back to my good ole SE-R, after about five years of hard use, the nuts had come loose. Two had actually fallen off completely and the turbo was hanging on the manifold by the other two. Granted, I forgot to bend up the tabs on the nut anti-rotation thingy, but nuts and bolts coming loose are a very common issue for bolted turbos. No such issues with v-bands. Considering the location of the turbo on the backside of the engine in this application, you definitely don’t want to have to go in there and fix a loose turbo. Swaintech is used again here to keep heat in the turbo and out of the engine bay.

 

APR even went the extra step to use Swaintech on the Tial wastegate!
No rubber lines used here for water and oil on the turbo. The rubber water lines on my SE-R cracked after about five years. Fortunately, I was at a gas station not too far from home when I noticed the mini water fountain of coolant spewing from my engine bay. The oil drain line is very OEM style and not cheap.

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