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Scion Tc - Supercharging Project tC

Part III: Smog-Legal Boost

Jul 30, 2006
0607_sccp_7z+scion_tc+right_front_view Photo 1/1   |   Scion Tc - Supercharging Project tC

Supercharging Project tC has been in the plans since day one. It's the easiest and most reliable way for an instant 60 wheel-hp boost that will give any tC a fighting chance against some of the competition out there, like the new Honda Civic Si, Acura RSX Type-S, or Chevy Cobalt SS. We've been waiting for ours ever since Scion announced the release of the centrifugal blower kit, but it's taken several months for TRD to finalize the product, get the emissions certification, and ship us a complete kit.

Although we've looked into various turbo kits and weighed the pros and cons of each type of forced induction, our choice to use the TRD centrifugal supercharger system boils down to three simple reasons: It really is a kit, there's a warranty, and most importantly, it's 50-state emissions legal.

The problem with the tC's 2.4-liter 2AZ-FE engine is its Camry origins. The cast-iron block and stuffy head were only meant for torque; great for city driving, but not for hauling ass. Even with the gobs of torque available from 2000 rpm, the 2AZ still runs out of juice above 5000 rpm. With such a narrow powerband and an open differential, turbocharging would make wheel spin an even larger issue than it is in stock trim. At 3000 rpm, right as torque is about to peak, a turbocharger would spool and cause wheelspin with the sudden ramp-up in power. Even with a larger turbo, top-end flow would still be limited by the head and cam profile and the massive lag of a big exhaust-driven compressor. But the 2AZ's merits can't be ignored either. The fact that it has a 9.6:1 compression ratio, dual overhead cams, and a tough cast-iron block makes forced induction an attractive option.

From a performance perspective, a centrifugal blower makes the most sense. Because a centrifugal supercharger generates boost strictly based on how fast the engine is turning, the amount of boost the blower makes has nothing to do with how much you mash the throttle. Unlike a positive-displacement supercharger, such as a Roots-type, the centrifugal blower will have a slightly exponential boost response curve because the compressor becomes more efficient as rpm increases. And since it's rpm driven we will reach peak boost and make more power at the very top of the range. Output wise, this keeps the power and torque profiles very similar to stock, just higher up.

The tC's open diff means we only have one 225mm wide tire to put down all our power, and we'd rather have boost that will ramp up gradually instead of all at once, creating an instant cloud of rubber from one wheel. If you have to ask why less power can be good, then look at why drag racers use rpm and gear-staged boost controllers on their big-boost turbo cars. Even with big, laggy turbos, when the boost finally builds, the rate of increase is too abrupt and often causes only wheelspin. For the same reason, a centrifugal supercharger's smooth and predictable power delivery is an advantage on a twisty mountain road or road course, when traction or talent is an issue.

The Kit
TRD's supercharger package is truly a kit in every sense of the word. With the exception of the ECU reflash, which requires a proprietary Toyota ECU programming unit, and the fuel line quick-release tool, all of the hardware can be installed in the driveway, without a lift. The kit includes everything from a new oil pan that already has a supercharger oil return spigot welded in, to new injectors, and colder spark plugs!

There are six basic portions to the kit: the supercharger, pulleys and bracketry, intake plumbing and airbox, new oil and fuel plumbing, fuel management components, and miscellaneous items including badges and EO exemption stickers. The kit uses Vortech Engineering's V-5 F-trim supercharger capable of flowing enough air for up to 475 horsepower at 20 psi. Obviously TRD overspec'd the unit, which as set up in the kit, is operating at the lower end of its efficiency range. All the better for us since we'll eventually step up the boost.

Installing the kit involves removing and installing a lot of the same parts you deal with in a routine tune-up. The airbox is partially pulled out and the injectors, plugs, and thermostat get replaced with 400cc/min units, colder K22PR-U plugs, and a lower 71 degree C thermostat, respectively. The oil pan is a straight swap as well, since the crossmember doesn't get in the way. In theory, the downpipe doesn't even have to be taken off, but it does make getting the oil pan off a lot easier.

The supercharger itself mounts on the transmission side of the engine, which means a driveshaft needs to extend from the pulley at the front of the engine to the blower. TRD supplies a cast-aluminum bracket that supports the blower and mounts to the bell housing, which requires temporarily pulling off the starter. On the pulley side, there are more brackets and pulleys for the longer serpentine belt, which realistically takes two sets of hands to thread: one to hold the belt and the other to turn the crank.

It's all nice and simple with a few exceptions. For clearance reasons, the fuse box needs to be mounted slightly forward. To do that, you have to split the loom on the harness leading to the fuse box, un-mount the box and re-drill a new bolt hole and then put the entire mess back together, all for less than 1 cm of clearance.

That isn't the most tedious part of the install, however. Special tools are needed for the fuel line removal and a dealer is the only place the ECU reflash can be done, which are both good reasons to have the work done at the dealership. Now, if you're considering not reflashing the ECU based on some online guy's advice or to save on the installation costs, think again. With larger injectors and a stock fuel map, you might get it to work, but it won't be pretty. In fact, it will probably run pig-filthy rich and cause all kinds of havoc on your hardware and throw your car into a limp mode in the long run. Plus, you'll void your warranty.

We went to Longo Toyota/Scion of El Monte, California, the largest Toyota/Lexus/Scion dealer in the universe, to get our supercharger installed. For five hours worth of labor, we have a smog legal, 200 wheel-hp, turn-key tC with a 5 year/60,000 mile warranty. A good thing, too since our pre-production tC had an incompatible ECU. Not only did Longo replace our ECU the next day under warranty, they also gave us a free rental car for the night.

Back at the track, our blown tC put down a 15.1-second e.t. at 93.4 mph compared to the stock car's 15.7-second run at 88.2 mph. From 0-60, the tC now takes 7.1 seconds, 0.7 seconds quicker than stock. For several thousand dollars, these numbers don't seem to do the kit justice. And they don't really do it for us either. Even with a continuously increasing boost curve, our hopes for top-end response were only marginally met. Instead, we just got a lot more midrange power and torque, which is still great for tooling around on the streets and cutting off unaware soccer moms and Civics alike.

Less slop and even less civilityIn addition to the blower, we also added TWM's Stage 2 short throw shifter and polished stainless steel weighted shift knob. It's a straightforward installation involving removing the center console, pulling apart the stock shifter assembly, and a lot of under-dash contortions. The only hard part, while you're in an inverted yoga position on the driver's seat, is trying to pop off some lock washers and the plastic snap-together mounts on the stock shifter. TWM supplies new lock washers and tools to remove some of the stock bushings, but you're up a creek if you break the stock mount that the assembly sits in.

The shifter does what most well-engineered short shifters do, shorten the throw and the height of the lever. Compared to stock, TWM's Stage 2 shifter is 2.5 inches shorter with a 35 percent shorter throw, which borders on being too ricey and clunky. If we were willing to tear it all apart again, we'd go with the Stage 1 kit that's only 0.50 inches shorter with a 25 percent throw reduction, which would take some of the unwanted notchiness out of the shift feel. TWM will also offer a set of rubber shift linkage bushings to go with its shifter kit soon.

The second and definitely more significant modification is Ingalls Engineering's "Stiffy." Appropriately named, the Stiffy is an adjustable hydraulic engine damper that sits on the passenger side engine mount and braces the engine against the strut tower and firewall on the same side. For all its bling appeal, this is one of the biggest improvements we've made to the car, but also the loudest.

We've deduced that since the tC uses a Camry engine, the mounts are most likely the same, i.e., soft and squirrelly. With all the torque the 2AZ puts down, the front wheels have to contend with both steering inputs and the twisting motion of the engine under heavy throttle. Around a corner, this means everything from road inputs to engine force translates back through the steering wheel, making it hard to determine what the car is doing. To take the twisting engine motion out of the equation, however, usually means replacing the engine mounts, for which there isn't a big demand in the tC community. Ingalls' Stiffy saved us this nightmare with a quick 15-minute installation. The kit includes a pre-set adjustable damper, some over-engineered brackets with its company logo on them, Dynamat for sound insulation, and all the bushings and hardware needed.

Although we got a huge improvement in steering response and feel, which makes the tC actually feel sporty, the incessant noise being transferred from the engine and valvetrain through the Stiffy and into the cabin makes us wonder if this is a worthwhile sacrifice. tC owners that frequently track their car will definitely want the Stiffy. But for the street, it leaves us feeling hard-of hearing.All that aside, we've made significant improvements to Project tC and are on the way to something we're proud to have in the fleet. Coming up will be some new exhaust plumbing to see if lower backpressure will help our supercharger push more air through the restrictive 2AZ head. Stay tuned.

Previous InstallmentsNovember 2005
Part I: Improving stickJune 2006
Part II: Bolt-on brakes for geeks

Sources

Wheels
Rancho Dominguez, CA
americanracing.com
Suspension
909-923-9188
www.buddyclub.us

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