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.