Toys 'n' the Hood

We installed a Seibon carbon fiber hood on the Mach V STI. The pictures here show it in its raw carbon form (it's finished in a clear gel coat), but it'll eventually be white like the rest of the car. We'll probably leave the side vents in carbon just to show the underlying material.

The hood fits pretty well -- it's molded underneath just like the factory hood, and it's got holes for the factory-issue windshield washer nozzles. It does come with silver aluminum mesh inserts, which we thought didn't really look good, so we removed those. The factory hood scoop doesn't have any mesh in it either...

The original purpose of carbon hoods on cars was to save weight. In recent years, a lot of carbon hoods don't actually reduce weight at all. The use of lightweight aluminum on the 02-07 WRX and STI, for example, meant that a carbon replacement weighed the same as the metal hood. But in recent years the price of aluminum has soared, and Subaru went with a steel hood for the STI. At 22 pounds, the Seibon carbon hood weighs a lot less than the 45-pound stock one. Hooray for actual weight reduction!

Note that we don't have hood pins on the car, but I've always recommended people use them with any aftermarket hood. Still, the Seibon hood is made with a metal plate imbedded in the fiberglass that holds the hood catch. Given the minimal amount of use our car gets, I may hold off on the hood pins until some future time when we're headed for the race track with the car.

Brittle Pistons on 2008 STI?

We've heard of an alarming number of 2008 STI cars that suffered piston ring land failures. Once the ring lands break, the engine loses power. Repair involves removing the engine and rebuilding it. Many of these failures were on completely unmodified cars. Subaru issued a recall on the car to reprogram the ECU in an attempt to remedy this problem, stating:

During a quality review, we discovered that under certain harsh driving patterns, specifically when repeatedly or continuously operating the engine above the “red-line” (RPM above 6,700), abnormal combustion could occur resulting in serious internal engine damage in the form of broken piston ring lands. This abnormal combustion condition is the result of an “over lean” fuel mixture caused by a combination of fuel cut activation and high turbo boost.

I'm not convinced the problem is ECU-related. Most of the failed pistons show no signs of detonation, although I admit that doesn't prove it's NOT detonation that caused the failure. Various theories have been advanced on the Subaru message forum communities, including:

• Crankcase oil is contributing to detonation which results in piston failure
• New materials used for the piston castings are more brittle than older ones
• Solid (not sodium-cooled) exhaust valves create in-cylinder hot spots which lead to detonation.

Personally, I'm leaning toward the "brittle casting" theory. It just seems like the pistons are more fragile than in the older Subaru 2.5 liter engines. Given the general trend towards cost-reduction, it would not surprise me if Subaru changed suppliers and that the new supplier used a slightly less sturdy metal formulation for the pistons. The bad news for us if the problem is caused by the actual piston construction, is that we will not be able to fix the issue just by re-tuning the car, or by any bolt-on modification. Only an engine teardown and piston replacement would solve the problem.

This problem hasn't surfaced on our shop STI (yet), but we're keeping our eyes and ears open.

Thanks to the guys at Turn-In Concepts for the picture above.

TPMS and You

When we swapped on the new wheels, we also installed the factory-issued Tire Pressure Monitoring System (TPMS) sensors, which would allow the car to keep track of tire pressures on our new wheels. Unfortunately, we broke a couple of them in the process, so we had to buy some new ones. And the car was not familiar with the digital code of the new sensors, so the dash cluster tire pressure warning light was always on. Some cars have an option to reset the tire pressure sensors right from the dashboard controls, but not this one. The only choice is to use a dedicated tool that can tell the car it's got new sensors on it. We'll eventually have one of these in our shop, but for now none of the aftermarket systems can work with the Subaru sensors.

So, down to our local Subaru dealership we went -- that's Dulles Motorcars in Lessburg, VA. A quick session with their factory scan tool laptop, and everything was working as it should. In fact, the next time the light went on, the outside temperature had droped about 40 degrees, and I found the right rear tire to be about 5 psi low. Hey, the TPMS actually works!

STI in the News

The December 2008 issue of Evo magazine arrived in the mail today, and it's the tenth anniversary issue. The first feature article compares the latest UK STI edition, the 330S (it has 325 hp) with the original 22B Impreza, which Evo tested in its first issue ten years ago. As you might guess, the 22B comes across as the better driver's car. The cars have almost the same power-to-weight ratios, but the 22B is under 2800 pounds, while the 330S is 3311. (A whole bunch of that is in the wheels, which are the five-spokers from our base-model US STI. And which weigh a whopping 27.5 pounds each.)

The article talks about the modern STI's lack of steering feel, and I concur. That is something I'm looking to remedy with some aftermarket parts in the future. I don't think I want to go so far as to swap steering racks, but I'll look into changing bushings and maybe some of the front-end suspension geometry in an attempt to get better steering feel.

Oh, and speaking of weight, we're looking forward to dropping 20+ pounds off the nose of the Mach V STI by swapping the stock steel hood with a carbon fiber one from Seibon. The hood is on its way to our shop by freight truck now, so I should have some pics of that in a week or two.

Rollin', Rollin', Rollin'...Keep Them Fenders Rollin'...

Somewhere many months ago, I said, "I'll find some wheels that fit better, because I don't want to alter the fenders to clear these." That was before I decided that the G-Games wheels are just RIGHT for the car. Not that I care -- okay, so I do care -- but 100% of the people who have an opinion also love the wheels. So they stayed, and to make sure the rear tires didn't collide with the edge of the rear fenders, we rolled the fenders.

You can do this a couple of different ways. The old-school way involves a baseball bat rolled between the fender and the tire. That's a little crude for my tastes, although there are people who can do it really well. We used a dedicated fender rolling tool, which bolts to the hub, and has a little urethane wheel and a screw that is used to press the wheel against the fender lip. It works well and makes sure you roll a nice circular arc. (The picture above is from Tire Rack. You can buy one of these tools from them, if you want.)

Mach V master tech Mike Gerber performed the delicate surgery on the STI, and the results are very nice. The fender is flared out ever-so-slightly -- so much that I didn't notice it at first -- so that it clears the outside edge of the rear tire. Mike made sure to heat the paint at the edge before rolling, so the paint did not crack. Before, the tires and fenders would rub together under any large suspension movement. Now, they don't seem to be able to touch at all. I've done some pretty hard cornering with the new setup, and have not been able to get them to rub.

At left is the fender and tire, post-fender-rolling. I'll be doing a bit more high-g driving to understand more about the results of our sway bar swap, and in the process I'll keep an eye on that rear tire/rear fender. Stay tuned.

I do have to make a note here about wheel offset for the 2008 STI. I've been seeing a LOT of 2008 STIs running very low-offset wheels. I think this is mostly because there are not many high-offset, large-width wheels on the market. Optimal offset for a 9.5" wide wheel on this car is probably around 50mm, but you'll be hard-pressed to find anything that wide, in anything CLOSE to that high of an offset. (As of this writing, I do have a set of 19" ASA's in the showroom. Email me if you're interested...) Most 18x9, 18x9.5, 19x9, or 19x9.5 wheels are in much lower offsets, like +30 or less. This kind of offset is great for a deep concave look, which I admit is really cool. But it also puts the tire really far out toward the fender, resulting in pretty serious interference problems unless you go with a narrow tire. So I've seen some people running only a 225 or 235 width tire so it won't rub. The car comes with 245s! I'd hate to go to a narrower tire just because I couldn't find the right wheel fitment. Some of the people who do this seem to really like the sticky-out wheel look, or the small-tire-stretched-to-large-wheel look. But in many cases these cars are severely compromised in terms of driving them every day, and in outright performance.

The other isse that nobody seems to talk about is that changing the wheel offset changes the scrub radius, and the steering feel is changed. For the worse. Even the relatively small (-15mm) change I made on our car resulted in a noticeable loss of steering feel, especially at higher speeds.

More Footwork: Whiteline Rear Sway Bar

We installed a Whiteline 22mm adjustable rear sway bar on the STI to try to get the car to rotate a little more readily. The stock suspension, even with the coilovers, has a marked understeer bias, meaning the front loses grip long before the rear. While this is safe, it makes it difficult to hustle the car around corners effectively.

A firmer rear sway bar can make the back end of the car more lively, and Whiteline's 22mm bar (up from the stock 17mm) is adjustable so we can tweak the stiffness at the back. Since we were back there, we also installed Whiteline adjustable rear end links. Installation was straightforward -- you could easily do this to a car on jack stands. Note that the sway bar kit comes with a set of sway bar support brackets (the gold-colored bar in the picture), which tie together the sway bar mount and the rear subframe. We think this is a great idea -- the stronger sway bar will put a significant amount of stress on its bracket. You can buy the sway bar supports separately if you want.

One note on the installation: The bar has a Whiteline label on the center portion. You would THINK that the label would face upright when mounted on the car. At least in this case, you'd be wrong. Putting the bar on so it'll clear the exhaust meant the label is upside down. Who knew?

The STI as Daily Driver: Thumbs Up

Compared to some of my previous daily drivers (cough! -- Lancer Evo -- cough!) the STI is extremely easy to live with. Even with the relatively hard-core Cusco coilovers, the ride is comfortable enough. And I had forgotten how useful and practical the hatchback layout is. Open hatch, pop down one seat, slide in a cat-back exhaust, box and all, and still have room for two passengers. It's quieter than older STI models, too. Talking with passengers doesn't require raising my voice.

I've come to appreciate the lighted steering wheel controls -- cruise control and audio functions are illuminated for easy identification at night.

The other part of STI ownership that I didn't expect is all the compliments and attention. At one gas stop I got three different people coming over and commenting on the car. I get thumbs up from random other drivers. One guy followed me to where I was going to ask about the car. Non-car people say things like, "I love your car! It's cool looking! What is it?" Not even the Evo got this kind of positive reaction.