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Project WRX: Part III

Part III: Faster, faster until the thrill of speed overcomes the fear of death

Dave Coleman
Feb 5, 2003
0303_01z+subaru_wrx_sedan+front_left Photo 1/24   |   Project WRX: Part III

Countless trips to Northern California, too many trips across the open desert to count, many, many rallycrosses and one 3,000-mile trek across the western United States at ungodly speeds. That's how Project WRX has spent the last year and half in our fleet. And it hardly cares. Sure, if it's pressed, it shows some wear, but considering the miles, age and pounding it takes on a regular basis, the little Suby has been nothing short of truly impressive.

0303_02z+subaru_wrx_sedan+underneath Photo 2/24   |   From below, the SPT (really STi) forged aluminum control arms are obvious. The new arms are both stronger and lighter than the WRX's original stamped steel control arms and come with stiffer bushings already installed.

What's more, it's likely one of the highest mileage WRXs still on the road. Our preproduction car arrived at our offices with 15,000 or so miles already on the ticker and as we write, it's clocked nearly 52,000. On the dyno, it's down about 10 hp to similarly modified cars. However, considering the lack of break in (this car was used at the press introduction where it was beaten senseless by a huge group of unrelenting journalists) it runs like a champ. We've had no problems that aren't in some way related to the pounding we dish out on a regular basis. And, despite all this, it remains perhaps the most effective tool in our fleet for dispatching miles of road--smooth or otherwise.

2017 Subaru Impreza
$18,395 Base Model (MSRP) 24/32 MPG Fuel Economy

This month, we'll test a new suspension, turbo, exhaust hardware and engine management.

Suspension

Hindsight is always 20/20. And when we look back at the string of logic that led us to settle on the SPT (Subaru Performance Tuning) suspension that's now on Project WRX, we, unfortunately, have some regrets.

0303scc_projectwrx03_z Photo 3/24   |   The SPT suspension kit for the WRX sedan is extremely comprehensive, including four springs, four inverted struts, both front-forged aluminum lower control arms, a smaller front anti-roll bar with bushings and rear crossmember bushings (not shown).

First, if you recall, there was the fight over whether or not we should even test this suspension. After all, Subaru's legal department makes it clear in documentation accompanying the suspension that SOA is well within its rights to deny warranty claims on WRXs fitted with SPT parts. Ironic, considering the parts are sold and installed at Subaru dealers around the country, which to us means they're given some measure of factory endorsement. Call us crazy. Not only that, but in many cases, the cost of the upgraded suspension (or exhaust) is amortized into the loan value before the customer even drives the car off the lot. So we didn't test it initially. There were other issues though. We found ourselves torn over what to do about suspension on Project WRX for several reasons. Most importantly, the stock suspension is very good. It offers reasonable damping, adequate spring rates, plenty of ride height and lots of travel.

0303scc_projectwrx04_z Photo 4/24   |   It's obvious looking at the bottom of an inverted strut that the shaft is below the body. This nut is used to locate the shaft to the strut housing.

Second, the alternatives we figured would work well, such as DMS or Proflex all offer the adjustability, damping and quality we were looking for. But that kind of flexibility comes with a price tag not so easily accessible to all WRX owners. Since we like to be somewhat financially realistic with the first round of parts we put on our project cars, we needed to settle on something less costly. Forcing us to make a decision was the constant pounding our stock suspension was taking and the fact that it was finally starting to get tired.

In the end, we knew we had to test the SPT suspension kit, which includes forged aluminum lower control arms, front and rear dampers and springs, a smaller front anti-roll bar with bushings and steel rear subframe bushings and sells for a reasonable $1,800 for the sedan. The SPT kit for the wagon goes for $1,500 but doesn't include the forged control arms because of the 10mm track width difference between the wagon and sedan. Both versions retain the stock ride height and all the dampers are inverted.

0303scc_projectwrx05_z Photo 5/24   |   Looking at the stock WRX struts next to the SPT inverted struts makes it immediately obvious why the inverted struts better resist side loads. Which one do you want under you if you're sliding sideways?

Inverted dampers are good for several reasons, but the primary advantage is that their design, which places the body upside down above the strut housing, is far more resistant to side loads than a conventional strut design. The shock body is located by large-diameter bushings, which more evenly distribute side loads, making the entire assembly more durable. And since side loads are what rally cars like the WRX generate when driven hard, inverted struts are good things to have. Plus, with the shock body above the shaft, the shock cools better than one which is surrounded by a strut housing as well.

Installation of our SPT goodies was performed at Frank's Irvine Subaru in Irvine, Calif., a dealer so aftermarket friendly it actually sells an extensive line of Subaru performance parts. Suffice to say Irvine Subaru doesn't void your warranty for SPT suspension parts.

Installation is a fairly straightforward job, similar to any strut car with the exception of the front lower control arms, which add some additional labor. The rear crossmember bushings also add time (and therefore cost) to the job. Plan on about $500 or the equivalent of about seven hours of labor if you pay to have the job done. If you tackle it yourself, you'll need a press to replace the rear crossmember bushings. Labor on the wagon, of course, costs less since the lower control arms aren't replaced.

Our car was already fitted with an adjustable Progress Technology rear anti-roll bar. However, since the SPT kit includes a smaller front bar, we knew further adjustment of the Progress bar would likely be necessary. A smaller front bar accomplishes the same thing as a larger rear bar, shifting handling away from understeer and toward oversteer.

0303_07z+subaru_wrx_sedan+top_left Photo 6/24   |   Over the course of the Stage One and Stage Two upgrades, our car made 224 dyno pulls on Vishnu Performance's Dyno Dynamics all-wheel-drive dyno. This is far more than normal, but since ours was the first car to use the Xede piggyback ECU, our car was the victim of quite a bit of research.

After an alignment to factory settings, we hit the road with the SPT kit installed and the Progress bar still on full stiff. Wow! This thing really rotates! It took us about three hard corners to figure out this combination was an autocross-only setup. The WRX now easily lifted an inside rear tire at low to moderate speeds and snapped around instantly when the throttle was closed rapidly mid turn. Not the kind of response we wanted on the open road. However, if autocrossing is your thing, this seems like a potent combination. We dialed the Progress bar back one notch and were able to find a good compromise between lift-throttle oversteer and understeer at corner exit. We briefly drove an SPT-equipped WRX with the stock rear bar and found it closer to the stock understeer-biased balance, but still more neutral than stock. On smooth roads, the WRX's manners were vastly improved. Gone was the lazy body roll of the old suspension, replaced by quicker turn in and better overall balance and control. However, Subarus aren't made for smooth roads, are they? The control gained at the limit on smooth roads comes with several compromises. First, our WRX feels lowered. It isn't. It just feels that way because of its ride quality. Railroad tracks that used to be ignored at full throttle now require serious slowing and hopes of not breaking a filling as the car crawls over them at half the speed. The SPT kit doesn't offer the compliance we were hoping for, which is odd considering it offers the same travel as the stock suspension. Little information is available on the dampers or spring rates, but our butts tell worlds about the combination.

0303scc_projectwrx06_z Photo 7/24   |   Many months of WRX tuning experience, some new tools, and a new dyno means more power is available for the same effort/money. Our car hit Vishnu's new dyno with an old tune, a strange preproduction ECU, and thousands of miles of self-learning. Swapping in a production ECU and letting Vishnu retune it, we picked up 11 hp.

We're not sure if the lack of compliance is a product of very high spring rates or ridiculous compression damping, but either way, the result isn't good. The WRX now bounces down roads it would have blasted across with the stock suspension. Bumps that used to be ignored now require attention. It's frustrating. We have extremely high standards for Subaru suspension and we want the best of both worlds--excellent road manners and the ability to swallow uneven terrain at stupid speeds. And we've driven Subarus in the past that manage both. Still, the SPT suspension showed an improvement in the slalom where the WRX posted 70.8 mph, up from 69.9 the last time we tested it.

But the SPT kit can't do both. It's a very cost effective solution if you're willing to live with some compromise over rough roads. But if you're looking for the perfect world, we suggest you look elsewhere. So we're moving on. We'll test another suspension soon in hopes of finding one that meets all our needs.

The magic box
We've been driving Project WRX with an early version of Vishnu's Stage Zero upgrade package (turbo up-pipe, underdrive pulley, colder spark plugs and a re-tune with various piggyback computers) for more than six months, and while we've enjoyed the huge improvement in power and responsiveness, there was one driveability issue that started bothering us shortly after our last update. Accelerating on boost at part throttle, the powerband felt lumpy. Instead of a smooth surge of power, it seemed to come in little hits and surges. It turns out this is an artifact of Subaru's engine management strategy not being entirely compatible with aftermarket boost controllers.

0303scc_projectwrx08_z Photo 8/24   |   Swapping the Supersprint exhaust for the Vishnu exhaust and retuning to take advantage of the drop in backpressure, we picked up 8 more peak horsepower and close to 15 hp around 5300 rpm. This was at the same boost. We credit most, if not all of this gain to the better design of Vishnu's downpipe flange.

The stock ECU normally controls boost, and in what must be an effort to dodge an emissions bullet, the ECU won't allow full boost unless you give it more than half throttle (55-percent throttle to be exact). The stock ECU also runs closed loop at these light throttle settings, meaning it constantly looks at the O2 sensor to keep the air/fuel ratio at 14.7:1. With the manual boost controller we have, or just about any electronic boost controller, you can get full boost at part throttle. This greatly improves throttle response and makes the car much more fun to drive, but if you don't mash the pedal, the ECU will still stay closed loop and the air/fuel mixture will be too lean (under these conditions, the engine would be safer and more powerful between 10:1 and 11:1). The result of this lean condition was the strange, surging powerband.

Over the last several months, we've tried various prototype versions of the EMI Adaptor, a magic black box Vishnu has been developing to solve this problem. The patented box watches for the high-boost, light throttle conditions that cause this lean condition, and sends a fake throttle positions sensor (TPS) signal to the ECU when necessary to fool it into switching to open-loop mode. In open loop, fuel delivery will be based on pre-programmed values in the stock ECU, all of which are nice and rich. Most versions of this box worked brilliantly, though just before the final production version appeared, we changed to an Exede piggyback ECU that was able to handle the box's functions itself, rendering the EMI Adaptor useless. It's still worthwhile on any WRX with a boost controller and either a stock ECU or any piggyback controller that doesn't specifically address the closed-loop part throttle problem. In fact, we'd go so far as to call it a critically important safety measure.

More power
We've been running a Supersprint exhaust and a Supersprint downpipe with an integral metal matrix catalytic converter. Although we were happy with the look and sound of the Supersprint system, the downpipe design was far from ideal. On boost, exhaust exits the turbo in two places, out of the turbine and out of the wastegate. The stock Subaru exhaust flange places the exhaust pipe directly behind the turbine, and a flat plate behind the wastegate outlet. Wastegate exhaust has to slam into that plate, turn 90 degrees and shoot into the main exhaust stream. At high power levels this can be a significant restriction to exhaust flow. Supersprint's downpipe, unfortunately, shares the stock flange design, and power gains from the downpipe were fairly minimal.

0303scc_projectwrx09_z Photo 9/24   |   This dyno chart graphically depicts both the advantages and disadvantages of a bigger turbo. Boost doesn't hit until about 3800 rpm now, but when it does, watch out! The engine's character is completely changed, now being much more eager to rev. Since the old turbo made the top of the rev band useless, the powerband is just as wide now as it ever was, it just starts later and finishes later.

There are countless other downpipes on the market at this point, but there are two that have really caught our eye as proper designs. Vishnu Performance's Signature Series exhaust has a divider wall that juts out of the flange, sticking into the back of the turbo and separating the two exhaust flows. Wastegate exhaust is carried in a separate exhaust pipe, where it bypasses the catalytic converter and joins the main exhaust about 18 inches downstream of the turbo. The other downpipe is from APS. The APS piece consists of a cast steel upper section that also utilizes a divider wall. The casting gently blends the two flows into a round outlet. A high-flow catalyst or a straight pipe can be bolted to the cast piece.

Because neither of these downpipes were available as of this writing, we used a simpler Vishnu exhaust and downpipe that gives the two exhaust flows a nice, tapered open chamber in which to work out their differences and get on with going down the pipe. At our current power level, this is probably good enough. The entire exhaust is polished stainless steel (ours had mild steel flanges, but stainless flanges are coming soon) and is built up by TIG welding countless mandrel bends. A large, high-flow catalytic converter is mounted after the downpipe, and an OE-style flex joint isolates the rest of the exhaust from engine movement. The entire exhaust is divided into four pieces that are bolted together with beefy flanges. The four-piece construction cuts shipping costs, but we feared that all those flanges, plus the many welded pieces, would cause a tolerance stack up that might lead to a poor fit. We needn't have worried. The welds were perfect, and the fit impressive. The exhaust passes within half an inch of the bottom of the car in several places, but never rubs. This is thanks in part to the full set of polyurethane exhaust hangers (in fashionable purple) that limits the exhaust system's movement.

0303scc_projectwrx10_z Photo 10/24   |   The stock downpipe (right) has a wall in front of the wastegate, giving the wastegate exhaust a tortured flow path that increases backpressure. The Vishnu Stage One exhaust simply opens this area, giving the turbine exhaust and wastegate exhaust some room to blend into a single flow.

Power gains with this system were convincing, making 8 peak hp and even more around 5300 rpm. And these gains are over an already healthy exhaust. The exhaust note is slightly louder and more clear than the Supersprint, but with the same deep, Subaru tone. One hundred miles after installation, with the polished muffler covered in dirt and road spray, the exhaust looks nearly stock.

Lots more power
Adding the Vishnu exhaust happened to place our car at Vishnu's Stage One level. Stage One is simply its Stage Zero upgrade, plus the exhaust. Naturally, we wanted Stage Two.

Stage One is effectively at the limit of both the stock turbo and the stock injectors. You could get slightly more power with these stock parts, but reliability would probably suffer. Stage Two, not surprisingly, is a bigger turbo (an IHI VF30, a close relative to the VF34 used in the WRX STi Spec-C), STi injectors, a high-flow fuel pump, a silicone intercooler hose and yet another re-tune with the piggybacks. Surprisingly, the intercooler hose alone is supposed to be worth about 8 hp.

0303_11z+subaru_wrx_sedan+rear_under Photo 11/24   |   The Vishnu Stage One exhaust fit surprisingly well, coming within a half-inch of the car in several places, but never rubbing.

Installation of all these parts is fairly straightforward. Even the turbo is a direct, bolt-in replacement for the stock turbo, including all the stock oil and water lines. Stage Zero was supposed to be a relatively simple install too, but it took us two days. This time, we had Doug Piper at Diablo Imports in Pleasant Hill, Calif., do the work. To our surprise, he never even used a Sawzall. Professional installation typically takes about 3 hours if all goes well.

The Xede piggyback ECU is the gem of Stage Two. This compact computer, with its no-wiring plug-in adaptor, hides under the passenger's feet with the stock ECU. The Xede is surprisingly well evolved, allowing better tuning than we ever thought possible with a piggyback. Five different signal inputs can be manipulated simultaneously, with each being adjusted up or down based on a high-resolution 20x20 map. Most useful, though, is the fact that the axes of that map can be anything you want. Rpm and boost, rpm and TPS, rpm and map, whatever. You don't have to use rpm either, but odds are you'll want to. Even better, the breakpoints of that 20x20 map can be set wherever you want. This becomes critically important when you see the goofiness that occurs with the stock ignition timing. There are dips and surges in the stock timing map that don't start and end at convenient 500-rpm increments. By moving the breakpoints of the crank angle sensor map (effectively the ignition timing map) to cluster around these areas, you can smooth the surges and dips more precisely. This flexibility helps on other inputs, too, where certain areas of the powerband might require finer control than others.

0303scc_projectwrx12_z Photo 12/24   |   Polyurethane exhaust hangers help keep the exhaust where it belongs, and the removable hangers on the muffler (primarily to simplify shipping) have a bit of adjustability, making it easier to center the tailpipes in the bumper.

Using one of these maps to fiddle with the TPS signal eliminates the need for the EMI Adaptor we added earlier.

Our car was the first Vishnu had tuned with the Xede, so there was a lot of learning while our car was on the dyno. More than two hundred dyno pulls of learning, in fact. In that time, Vishnu found some limitations of the system, all of which Chip Torque (the manufacturer of the Xede) is addressing within weeks of this writing.

Because the WRX watches the relationship between the crank angle and cam position sensors to watch for misfire, the updated Xede will manipulate both together. This will eliminate the flashing check-engine light we have now, and allow the system to be used on the upcoming STi, which compares the two signals to control its variable cam timing. In fact, the cam position signal will be able to be offset from crank angle signal to change the cam timing. The system will also have the ability to do closed-loop boost control using the stock boost control solenoid.

0303scc_projectwrx13_z Photo 13/24   |   The IHI VF30 turbo looks nearly identical to stock at first glance, but look in the center of the compressor and you can see how much bigger the compressor wheel is in the new turbo (on the right).

Perhaps most exciting, the Xede can be re-tuned by downloading new maps from the Vishnu Performance Web site and uploading them to the Xede yourself. With the constant, obsessive fine-tuning Vishnu is known for, being able to keep on top of the latest tuning updates can be invaluable.

Driving it
Stage Two has completely changed the WRX's engine. What once was torquey and responsive in the midrange, and frustrating at high rpm, is now noticeably softer at lower revs, and shockingly powerful at high rpm. The powerband is very reminiscent of the Lancer EVO VI we tested way back in May 2000. The engine pulls so strong at high rpm that bouncing off the rev limiter is now common. High-rpm breathing is so much better that the 7000-rpm redline seems too low.

Dealing with the extra lag of the bigger turbo means changing your driving style a bit. With the stock turbo, you can lug around off boost, short shifting all the time, and still expect to have a good surge of power whenever you put your foot down. With full boost not available until 4000 rpm, thrust on demand with the new turbo requires that off-boost cruising happen at higher rpm. Stab it at 2000 rpm and you have nothing. At 3000 you'll get a smooth, gentle increase in output. Jump on the gas at 4000 rpm and you better not have anything in front of you.

0303scc_projectwrx14_z Photo 14/24   |   From the turbine side, the wheel is also significantly larger, but look at the size of the turbine housing (just behind the exhaust flange) and you can see why the new turbo (on the right) causes so much less backpressure, and why it takes more exhaust energy to get it spinning.

Shifted like a Honda, making gear changes around 5000 rpm when cruising around in traffic, massive wads of power are available whenever you want. So what's next? How much power is enough? How far are we going to go with this?

Turns out a clutch has to be next on the list. Our first, and only, attempt at recording a new quarter-mile time with this setup resulted in a 13.4 at 104.4 mph, with a bunch of stinky clutch slip. Our calibrated butts say 13 flat should be easy with a good clutch, but that will have to wait until we have one. A fresh, healthy stock clutch should handle this power, but our car has 52,000 miles on it, and dozens of 13.5-second quarter-mile runs on the clutch, so its tired state can be forgiven. An APS top-mount intercooler is also in the works, as ours is no doubt getting a bit hot at this point. And finally, we have two more suspensions planned: a DMS street setup, and Bridgestone's Praxis air suspension. n

Gauges that should be stock

The biggest challenge installing gauges in a modern interior is finding some place to put them. An A-pillar mount, if you can stand the rice factor, is great for a single gauge, but put two or three there and they all end up different distances from your eyes, making quick gauge checks impractical. Omori Meter's OE-look gauges and Subaru's own dash-top pod solve this problem brilliantly. Omori is making gauges with faces and needles to match several different stock instrument clusters, including the WRX and MINI Cooper. Three of the small, 45mm gauges will fit in a single-DIN hole with Omori's angled single-DIN mount. Converting to a single-DIN stereo will allow you to put this in the dash, but there is an even better solution. Subaru's own dash-top pod, which we got from Irvine Subaru, replaces the dash-top digital clock with a pod and a mounting bracket for any DIN-sized accessory.

0303scc_projectwrx15_z Photo 15/24   |   The stock heat shield has to be trimmed to clear the new turbo. With the intercooler mounted just above the turbo, you don't want to leave the heatshield off.

It took a little trimming of the plastic pod to accommodate the angled face of the Omori gauge mount, but otherwise, installation was simple. Switched power, illumination and ground wires for the gauges can be wired straight to the old digital clock harness.

We filled the pod with oil pressure, water temperature and oil temperature gauges. Boost and exhaust gas temperature (EGT) are the two most critical for a turbocharged car, so we wanted a larger, easier-to-read gauge. Omori makes a large, 80-mm boost gauge with a digital EGT readout in the center. Perfect. This large gauge fits in the round air vent to the left of the steering wheel. Losing this vent might mean a numb left hand on cold winter mornings, but since we don't have cold winter mornings in Southern California, we don't care. n

Sources

Vishnu Performance
Danville, CA 94506
866-584-7531
http://www.vishnutuning.com
By Dave Coleman
94 Articles

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