This is the upgrade I thought I’d never do because it increases maintenance needs and removes some of the low-end torque that I really enjoy… and it’s expensive. Still, I would have instinctively seen an IS38 as a good upgrade if my original turbo had failed. Well, with 128,730 miles on the odometer, I got bored and decided to make a leap to greater power! I took the car to my APR dealer, Euro Pros in Yorktown, VA, and had them install an IS38 turbo and update the software. The IS38 is the factory turbo found on the Golf R and Audi S3. In fact, we acquired my turbo from a local Audi dealer to insure that we sourced the latest revision. Also, APR recommends NGK-R7437-9 spark plugs, which have been backordered for a while. Instead, Euro Pros installed OEM spark plugs for an Audi RS5, P/N: 06M905606F, also acquired from a local Audi dealer. The RS5 plugs work great, are half the price of the NGK racing spark plugs, and have a longer service life.

APR’s advertises Stage 3 as outputting 395 hp and 376 lb-ft while using 91 AKI fuel. My output may be a little less since I use the factory airbox with an OEM filter element. However, I have removed the snow screen and added an ECS “Big Bore” turbo inlet pipe to the mix. So, who knows, especially given that the stock intake flows more than enough air to support 400 horsepower? Mathematically, the Stage 3 power improvement is just ~17% over Stage 2. Shoppers often overlook the big picture by considering only peak numbers. This dynograph composite marks the difference “under the curve.” With that said, look at where the additional power is had… above 5000 rpm! Translation: You won’t necessarily feel a difference during regular driving or your daily commute, but the car will jump to life when revved higher.

On the other hand, there’s the loss of low-end torque. This dynograph composite marks the difference in low-end torque between Stage 2 and Stage 3. As a long-time TDI driver, I have a great appreciation for low-end torque and a (bad?) habit of driving lower in the engine’s power band as a result. A Stage 2 car is quite responsive below 3000 rpm. So, I didn’t suffer much of a penalty in driving my Stage 2 car “like a diesel.” Now that I’m Stage 3, I tend to be a bit more aware of the loss of low-end torque. I could tell the difference on my first drive. But it didn’t take long to become accustomed to the new driving dynamic.

Driving sedately, I find that I need to apply just a little more go-pedal to accelerate the same as with Stage 2. It’s not enough to ruin the drive, but I can feel the loss. In second gear, Stage 2 can feel responsive at around 1800 rpm and then easily trigger the traction control around 2500 rpm. Stage 3 seems dead below 2300 rpm, but then unleashes its fury at around 3000 rpm. Some describe the delayed response as “smoother.” I understand that. Rather than having the tires break loose instantly at 2500 rpm, a point at which I might be looking to make a quick lane change or pull out of an intersection, the delayed response from the IS38 gives me about 500 rpm, or maybe an additional second or two, to think about what I’m doing. HAHA!

The most obvious maneuver in which I notice this behavior is when I’m making a slow turn in second gear at around 1500 rpm. With Stage 2, if I needed to stab the accelerator to jet through an intersection, I could pull away from 1500 rpm with confidence and then with authority by 2000 rpm. With Stage 3, the car just meanders through the intersection. Yes, the car is still accelerating below 3000 rpm; it’s just not exploding the tires off the wheels. Part of this slower spool is because the compressor and turbine wheels are 7-8% larger than stock. So, the IS38 isn’t quite as fast to spool.

However, it’s moving more air once it’s spooled. Stage 3 gets exciting in third gear, which is where traction is easier to maintain above 3000 rpm. Assuming that I’ve started an acceleration effort and have already surpassed 3000 rpm, third gear will swiftly take the car to over 95 mph. An IS38 upgrade makes the car very eager to send me to jail! If you’re already tuned with anyone’s Stage 1 file, then you may recall that Stage 1 in third gear pulls with the same intensity as the stock programming in second gear; then fourth gear is about two-thirds the intensity of third gear. With Stage 3, third gear pulls with the intensity of Stage 2’s second gear pull, and fourth gear continues to pull as hard as third gear. The car just PULLS! It’s a beast, but a well-tempered beast that’s still conservative enough to operate at safe levels.

Remember – The IS38 is an OE turbo, just not for the GTI. Sure, some tuners can and have achieved higher output numbers from their IS38 tunes than APR. Those tunes may or may not be the reason for a number of reported IS38 failures and the call for the stronger hybrid turbos. Still, even with the APR Stage 3 program’s alleged short-comings, the same criticism about it being an “off-the-shelf” tune is what compels me to appreciate it. My Stage 3 IS38 is basically operating at the same level as a Golf R (IS38 is standard) with a Stage 2 tune, assuming both tunes are designed within the safe limits of the IS38. The primary difference, and it’s big, is the fact that I don’t have rear drive wheels to launch the car. Regardless, my GTI is swift and can possibly outpace a tuned IS38 Golf R beyond 40 mph due to its weight advantage and lack of rear driveline drag.

Coming from a diesel background and having done some fuel economy testing before, you know that I took the car on a road circuit to see how the IS38 affects fuel economy. To be more accurate, my goal was to see if an IS38-equipped GTI could still acheive good fuel economy. I was so surprised by my run that I did a longer run the following weekend just to see if it was repeatable. I will share the results in my next article.

Traction-Limited,

Scott