Tuesday, November 24, 2009

Uncorking the Power!

In that never-ending quest for more horsepower, we've been experimenting with some different parts on the STI. But as I've mentioned before, paying customer work has a way of coming before our own shop car. The good news is, this customer wanted to put almost the exact same modifications on his 2010 STI, as we have on our 2008 model. (Despite being different model years, the cars are mechanically identical.) We wrenched for a few days, then strapped the customer's STI up to the trusty Dynojet dynomometer for some testing. Would it surpass the Mach V STI?

Here's what we put on the car that's the same as the Mach V STI:

Here's what's different from our car:

One extra note about my tuning this car: It's a 2010 model, and at this point in time Cobb Tuning's wonderful AccessPort is not compatible with the brand-new ECU. The only way to tune this car for now is Open Source software available on the Web.

I don't usually use this approach for a several reasons. The first is that the results of my tuning can (in theory) be easily read by someone else, where the AccessPort gives me some amount of rights management over the ECU tune I create. The second is that the Open Source stuff does not allow "real time" tuning. For each change you make, you have to re-flash the ECU, which has traditionally been pretty time-consuming. (Early systems from four years ago would take 20 or 30 minutes for each re-flash.) The final reason is that the software has often been a little half-baked. I tried an early version a couple of years ago and there were some major bugs.

Things have come a long way since I last tried this stuff out. Although I still worry about my intellectual property a little, the speed of the re-flash has advanced to where it takes less than a minute to shoot a change to the ECU. And the software was stable during the whole tuning session, with no obvious bugs or problems. It still takes me a bit longer than the AccessPort system, because I'm using several different pieces of software and having to switch and move data between them. But most of the gripes I previously had with the Open Source stuff have been addressed.

This customer wants to use his car for track day use at road racing courses. That means the car will see very hard use, with high heat loads and much longer times on-throttle than any street car will ever see. I planned to be conservative with boost, fuel and timing.

Despite those guidelines, the car still made great power. The chart at left shows our own Mach V car (green lines) on a run where the boost and timing were similar, graphed against the 2010 car. Since there are some substantial breathing differences -- the headers, induction pipe, and the TGV deletes -- I can't say whether or not the turbocharger is responsible for all that additional power. But this combination of parts certainly woke the car up.

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