After the IS20 turbo blew I was a little overwhelmed. What to do? I didn't want stock power again, but a tune on an IS20 was too much here in Salt Lake City. I talked to a number of Mk7 Members and Dan Little of Little Co turbos directly. The consensus was the only real option at altitude was to run a bigger turbo to compensate. Lucky for me, I was patient with a seller and managed to scoop up my IS38 turbo for a low $670, shipped!
To balance or not balance?
Because so many IS20 turbos have failed, people have started to look at balancing both IS20 and IS38 turbo. Data supports significant error from the factory on a number of turbos. However, the cheapest place (GPop Shop), would have been ~$70 shipping each way + $100 balance. Since this was an already unexpected expense, I wasn't quite ready to shell out another $300. I took the turbo to a local shop, Industrial Injection. Visual inspection suggested there was nothing wrong with the turbo, and there was really no reason to rebuild it. Screw it, then I was going to put in as is.
So, when a turbo fails as mine did (shaft in two pieces), it leaves a mess. Oil ends up all over the intake tract, and shrapnel from the compressor wheel also get basically everywhere. So I cleaned. I removed every piece of intake piping, the intercooler, leaving only the intake manifold behind (I simply didn't trust myself to properly reinstall it). I back flushed the intercooler for a solid 5 minutes straight with high pressure water. So much crap came out. Can't imagine my car would still be running otherwise. The moral here: if you blow your turbo -- CLEAN!!!
I'm not going to go through a detailed description here, but I will explain the procedure briefly, as just knowing the order helps immensely.
1. Drain oil and coolant (Optional, but highly suggested as it makes a mess)
2. Remove intake components (airbox, turbo elbow, etc.)
3. Remove hard coolant line
4. Remove ignition coils
5. Remove cam actuators
6. Remove oil and coolant feed lines
7. Remove downpipe (optional)
8. Remove turbo bracket
9. Remove turbo!
I've probably missed a few things, but that basic procedure should get you through most of it. Truly, it's not that crazy of a job. But when you don't know the order, a bit intimidating. Installation is the reverse. Make sure before you start the car, you unplug the ignition coils and crank the motor for a solid 10-15 seconds. This primes the turbo with oil!
I'll firstly state for daily driving, the IS20 is actually superior. The low- and mid-range response is fantastic, and the IS38 certainly doesn't pull as hard as the IS20 up to about 3000. It's really not til after 4000 that it shines. For the first 3 months of this turbo, I ran on Eurodyne's IS20 Stage 1.5 file. Remember, I'm at altitude, so I have to "detune" the car. This works pretty well because the ECU is closed loop, and targets a lambda and boost level, so even with increased airflow of the IS38, the car still runs well.
One thing I absolutely love about the IS38 is the top-end. I come from a history of 2.5L Staight-6 BMW engines (more on that later), so I love spending time between 4-7000+ RPM. It's a magical place, really. The IS38 takes a step toward this magic, and really prompts you to spend time between 4500-6000 RPM. Even all the way up to 6500 feels really great. It still catches me off guard how hard it pulls after 6000. Seeing that redline creep up at 6000 still prompts me to shift early sometimes.
While this power band does mean giving up a bit on daily, holy crap does it pay off on track. The GTI gearing for my local track is actually really good, being that the course is between ~50 and 110mph for my car (probably most cars, I doubt many see more than 120 on the straight). Either way, this is just at the bottom of 3rd and gets me well into 4th. The GTI screams through this range, especially in the mid 3rd gear corners. Even with my WaveTrac LSD and RE11 tires, I can spin both tires mid corner laying into it.
Response of the turbo is great too in this 4000+ range. Lag is minimal, but modulation can be challenging. I believe this mostly to be an artifact of the tune itself, as sometimes going from 50 to 60% throttle feels more like going from 40 to 70% throttle. I currently run an updated tune, and the issue is definitely not nearly as prevalent. Nevertheless, I do miss that NA response sometimes!
To put some numbers behind it, a typical IS20 tune peaks ~25psi and tapers to 17psi by 6500. Conversely, a typical IS38 tune peaks ~26psi and tapers to a pleasant 20 psi at 6500. The result? A very strong top end. I really can't stress that enough. All the graphs in the world might suggest the IS38 feels weak above 6000 (since peak power is right about there), it honestly rips hard to fuel cut-off. While it's not rev-limiter bashing VTEC goodness, it's still pretty fantastic. If you have the means, and your building a track car, I think the IS38 is really a fantastic option.
Next up -- suspension!