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

by Khiem Dinh

Photos Courtesy of APR

Khiem Dinh is an engineer for Honeywell Turbo Technologies at the time of this writing.  All statements and opinions expressed by Khiem Dinh are solely those of Khiem Dinh and not reflective of Honeywell Turbo Technologies.

I’ve been messing around with turbos and turbo kits for more than a decade in enthusiast and professional capacities. When I saw this APR kit released for the Audi TT RS, I was extremely impressed. It is the best kit I’ve seen released for any car, bar none. Even better than the $100k kits used on some very exotic cars. What makes it the best? It’s all in the details as they say along with the engineering process used to design and develop the kit. Follow along as we examine how the kit was made and analyze why it’s so good.

You could say I’ve been around the block a few times when it comes to putting turbos on cars. It all started with my good ole Nissan SE-R. Then I helped a buddy turbo his Civic. Then I helped a buddy turbo his 240SX. Then I helped a buddy swap turbos on his Z32 300zx. And a FC RX-7. And a FD RX-7. And a Scion tC. And an Evo X. There are probably a few other cars I have forgotten. Along the way, I’ve learned lessons in how to make things reliable (I racked up 80k miles after installing the turbo on my SE-R which saw plenty of hard use and track time) by breaking things. Having had a hand in developing some kits, I’ve learned a few things in the design process too.

In the modern design world, everything is done on computers with 3D modelling. Why? It allows you to accurately design and test fit many design iterations of components in a virtual world before committing to real hard parts.


In order to create the virtual 3D environment, you need models of the components. If you’re a company (such as APR) designing stuff for someone else’s stuff (like Audi cars), you’ll probably have to create your own models. APR has a cool tool which is a hand held 3D scanner. The little circular black and white dots are placed on the object you want to scan to give the scanner very well defined reference points which improves the accuracy of the scan. Some very expensive scanners have a resolution down to microns creating very exact models.
The super high resolution 3D scanners can cost a gazillion dollars, but this Faro arm does not (still not cheap however). The Faro arm allows for very exact measurements which you want when taking measurements of the head. The more exact the measurements, the better you can design your own components (such as the exhaust manifold to bolt to this head). It is clear APR has invested heavily in the tools to do good engineering work. There is a lot of capital cost up front, but huge savings in time and reduced design iterations down the road.
Once you have your 3D model environment set up, all the parts can be designed and virtually test-fitted.

Once everyone is happy with the designs, parts need to be test-fitted. APR just happens to have their own stereolithography machine to generate rapid prototypes. Stereolithography uses a laser to solidify a liquid polymer and it builds parts a layer at time until the final 3D piece is created. Why do you need to test fit? Well, many things don’t become apparent until you actually try to put hard parts on the car. For example, a part may be designed to fit within a space, but after much @#$@ @#@$&!! Why won’t it &*#@ go in!%!, you realize the part you designed can’t actually get to its final resting space. Or, something is in the way of getting being able to put a wrench or socket on a bolt. Or when the engine moves, something will hit something else. These are just a few of the issues that become apparent once you start trying to install parts on the car.
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Monday, October 14, 2013 2:45 AM
"APR investment cast the manifold from Inconel"


That. Is. So. BADASS!

My dad runs the engineering department for a manufacturing firm that specializes in making components for aerospace turbine engines. Specifically, they do parts for the 'hot section' almost exclusively. That means "combustors" for the most part. We're talking about parts that have to live at temperatures which absolutely dwarf anything seen in the automotive world along with pressures and flow-rates that are top of the heap for *any* type of internal combustion engine.

In his world, Inconel is pretty much bottom-of-the-barrel in terms of materials. It goes up from there to various Titanium derivatives, Waspaloy, on into the ultra-exotic proprietary stuff like GE's René series alloys and beyond.

So, we're talking about a guy who is not easily impressed when it comes to material science or engineering fit-and-finish. He's a proper gear-head, but generally doesn't care much for aftermarket kits such as this. In an attempt to show him that the automotive performance aftermarket is moving in some seriously high-tech directions I showed him this article.

It actually made him utter the words: "That's pretty badass."

By far the highest praise I've ever heard for this type of product. Khiem, your assertion that this is the best turbo kit made for any car is definitely not hyperbole. Seriously impressive stuff. I hope APR sticks with it and develops more kits of this quality for other platforms. I would *love* to see this kind of thing set the standard for performance parts at large.

Great write up!
Monday, October 14, 2013 2:57 AM
Oh, and regarding all the added power this kit gets from extra octane, would this not be an ideal opportunity for some kind of ethanol conversion? Methinks that E85, what with it's 105-ish octane rating, would be an ideal explodey juice to run in one of these monsters. I know you would need monster injectors and that extra work would be required throughout the fuel system. However, I feel like the high octane, low EGTs, low cost and road-legal status would conspire to make such an effort worthwhile.

Do you know if APR has looked into that at all?
Monday, October 14, 2013 8:17 AM
Very cool to see aftermarket companies start producing kits that rival OE for build quality and reliability. 600 at the wheels is insane for a "bolt on" kit. I assume the internals wouldn't support these numbers though.

Also, looks like it doesn't ship with an IC. I can see wanting to run your own when putting these numbers down but it seems like one should be included in the kit.
Monday, October 14, 2013 8:40 AM
@Drunken, I don't think E85 is currently feasible due to the limitations of the DI fuel system. I don't think it's possible to get enough mass flow rate. I could be wrong though!

@Protodad, this is indeed on stock internals. I was a bit surprised myself, but not overly as this is a RS model Audi. The old school SR20DE only put down 120whp stock, but the guts could handle 400whp all day long. The good ole 4G63 was also a tank of an engine with guys doing 500whp on stock guts for an engine putting down 240whp stock in the Evo.

As for the IC, I believe it was developed much before hand and has been available for some time. So it makes more sense to sell the kit without the IC as many of their potential customers already have the upgraded IC. I believe that's the logic behind Garrett selling their GTX turbos without turbine housings; many people already have turbine housings on their current setups, so it saves the end user costs by not forcing them to buy a new one when they can reuse the old one.
b drecksage
b drecksagelink
Monday, October 14, 2013 10:53 AM
Too bad the tt rs costs a lot of money. I love that car, just cant afford 60k right now
Monday, October 14, 2013 12:16 PM
What wall thickness did they use on the manifold? I could see it being worthwhile if you could go to 2mm walls or something, but if you're at 4mm then there is no benefit over using 1.4848 stainless, especially since the TH is stainless anyways.
Monday, October 14, 2013 4:41 PM

Ahh, of course, I forgot that it had Direct Injection. I am familiar with how problematic it is making significant mods to such systems. That's too bad :\
Dan DeRosia
Dan DeRosialink
Monday, October 14, 2013 5:01 PM
Cool piece. I really want one of those handheld scanners too. Well, and a TT-RS but nevermind that, heh heh.
Monday, October 14, 2013 5:30 PM
Matt, I don't know the thickness. Inconel does have a lower thermal expansion coefficient than 1.4848, so I think that should reduce stress due to thermal expansion and contraction thereby improving fatigue life. Inconel is also significantly stronger at elevated temperatures; I've worked on some parts that were initially HK30 SS that we had to switch to Inconel because the HK30 failed at elevated temperatures by bending.
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