Mod: Tribeca (H6) 130a Alternator Upgrade

After the Christmas cold snap, I had some issues with my BRZ EPS setup. I thought I had chased down all of my issues, but a new one popped up. I had a couple of things happen while driving home from my in-laws late in the evening on Christmas day. My WRX cranked very very slowly but fired up. I let it idle for a few minutes as I said my goodbyes. As I backed out of the driveway, my HID headlights shut off. This was alarming, but I turned the switch off and on, and they came back on. At the time, I thought it was either a ballast or a relay issue, as it was around 15 degrees.

It is about a 45min drive home, and about 80% of the way back, my EPS cut out. I was on the highway, so I don’t know exactly when this happened. Sometimes, turning the car off and on will fix this; however, this time, the EPS shut off again shortly after a reset. I only had a couple of sharp turns remaining, and they were all in my neighborhood, so I just toughed it out.

After I got home, I wondered if the alternator was the problem. I think this is the first time in a long time that I have driven in temps this cold with headlights on, heat on full blast, and the EPS setup. I think the EPS controller shuts down whenever the battery voltage drops below a certain point, but that is just an idea at the moment. I intend to upgrade the charging system anyways since I plan to add one or two more electrical components. I bought a cheap voltmeter gauge from Amazon to monitor my voltage while driving.

At warm idle, it was at 14.8v (+/- 0.2v) and while cruising it was around 14.5v (+/- 0.2v). While turning the steering wheel, it would drop to around 13.8v, depending on the surface and my speed. The average drop was around 0.2v or 0.3v. Headlights would drop the voltage about another 0.2v to 0.4v. The heater blower would drop another 0.2v or so as well. Running the headlights and the blower put the voltage around 14.3v. Although it was hard to monitor the gauge while making a tight turn. It would occasionally dip into 14.0v before rising back up.

In retrospect, I think my battery is just too small to deal with HIDs and an EPS setup, and a stock alternator. I don’t drive this car much, which isn’t helping either. Looking at other Subaru models with EPS, they all have 130a alternators.

After some research on Nasioc, I found that the 2008-11 Tribeca 130a alternator is a direct swap. I picked up a used one from LKQ, but Maniac Electric sells what appears to be re-maned alternators for a decent price. They also sell rebuild parts. I initially looked at BRZ alternators, but the mounting points are different.

It is hard to tell from the photo, but the 130a alternator is bigger than the EJ207 90a. It also weighs about 3.5 lbs more. It also had one more rib on the pulley. I could have swapped them, but I already run a belt with one less rib due to the EPS swap. I plan to pick up a lightweight pulley from GNP at some point.

The harness connection is the same 3-pin, and the output post is angled slightly differently, but it wasn’t an issue.

It is a tight fit, but it fits. It almost looks like a generator sitting in there.

On cold start, my voltage was at 15.2v. The stock 90a alternator put out 15.0v, so this wasn’t too alarming (and the gauge probably isn’t super accurate); however, even at warm idle, it stayed at around 15.0-15.2v. I forgot about the diode mod. I put a 10a fuse in, and the voltage dropped to 14.5v (+/- 0.2v) at warm idle. While cruising, it was around 14.3v (+/- 0.2v).

Overall, I will say this alternator is a good option if you need more amps. I thought this alternator would hurt performance, but the EJ207 seems a little peppier. Could be something, could be placebo. I am not sure.

Unfortunately, this didn’t solve my problem. It still shuts down, although less frequently. After some more research, I think the BRZ EPS setup just draws a lot of power. The EPS has an OEM fuse of 80a, which means the system could pull most of the stock alternator’s 90a output during heavy use, depending on RPM and temperature. Factor in HIDs, fuel pump, blower, ECU, etc… and the OEM alternator and small battery may have been at their limit, especially in the cold weather. It’s just weird because I drove for 6hrs a month prior with no issues.

Next, I will redo the power/ground wiring (actually, I have already done this). A lot of this setup is still in proof of concept phase. I want to see if there are any improvements before I replace the battery to minimize my variables.


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