2008 Subaru WRX - Tomioka WRX Turbo & Equal-length Header Upgrade - Proving Grounds - Modified Magazine

Test Mule
’08 Subaru WRX
Engine
2.5-liter EJ25 turbocharged boxer 4-cylinder
Relevant Mods
Aftermarket downpipe, after-cat and air intake.

Description
The ’08 Subaru WRX has been equipped with one of the smaller turbos that have come with WRXs in years past. It’s great for low-end grunt, but quickly falls flat on its face when the revs begin to near redline. Tomioka Racing has addressed this concern with a bolt-on turbocharger solution. The TR TD05-20G turbo has been built to fit in the factory turbo location and connect to all the water and oil lines just like the OE turbo, meaning there’s no customization needed to make this turbo work.

Knowing that lag would be a concern for many ’08 WRX owners, Tomioka built the TD05-20G to reflect a perfect blend of response with high-end output. With potential to deliver more than 400 hp, the TR TD05-20G seems like the ideal turbo to replace the tiny factory unit, while the Tomioka Racing equal-length headers help smooth out and increase exhaust flow with larger-diameter piping. The combo should provide some great power gains while minimizing lag.

Key Features

Tomioka Equal-length Exhaust Manifold

• All stainless steel construction
• Equal-length, smooth, larger-diameter tubing
• 3-bolt flange designed up-pipe to ensure leak-free operation
• Comes with heat wrap and all the necessary gaskets for install

Key Features

Tomioka TD05-20G Turbo

• Capable of up to 400 hp while maintaining street-friendly characteristics
• Larger turbine wheels provide mid- to high-end horsepower without increasing lag
• Turbo comes with all fitting and gaskets, ready to bolt onto the stock location of your factory turbo

Results
One of the most important concerns the owner of this ’08 WRX had was if a turbo upgrade was going to affect the fuel economy of the car badly. “I use the car for the daily commute. Naturally, I don’t want to increase my fuel expenses after the upgrade,” he says. Since the WRX already had an aftermarket downpipe, after-cat and air intake but had never been tuned, the car averaged 22 mpg. That’s a real concern these days with gas prices skyrocketing. The key, though, is the driver. If you have a heavy foot, then gas mileage will drop, but if you do a turbo upgrade and drive the car like you normally would, fuel economy shouldn’t suffer.

The Tomioka Racing TD05-20G turbocharger is rated at 400 hp, and it’s a bolt-on unit that can flow 640 cfm. It’s quite an upgrade from the factory turbo, and when coupled with the necessary mods (like a Tomioka Racing equal-length exhaust manifold, 800cc injectors and Walbro 255-lph fuel pump), the turbo should be close to reaching its target numbers. Remember, a turbo upgrade is useless without supporting mods.

But before the wrenching could begin, the WRX was slapped on the dynapack dyno at EDO Performance, where Edwin Tang did a quick tune to maximize the stock turbo’s potential, and the car put down 222 whp and 226 ft-lbs of torque.

As mentioned earlier, the installation of the TR TD05-20G is fairly straightforward since it fits just like the stock turbo. While the new turbo was being fit into place, the fuel pump and injectors were swapped for larger units to ensure there would be adequate fuel delivery.

Next on the list was the equal-length manifold. The Tomioka Racing equal-length exhaust manifold’s larger primary tube design increases exhaust flow to the smooth merge collectors, increasing spool-up while making more power. Tomioka uses a 3-bolt up-pipe flange to avoid blowing out the lower gasket, as is a common occurrence with the 2-bolt up-pipes. Tomioka also includes a roll of heat wrap to trap exhaust heat where it should be and not in the nearby oil filter or oil pan.

With all the mods installed, it was time to see what the power output would be. Edwin began tuning the WRX and at one point power jumped to more than 300 whp. Unfortunately, the stock intercooler was showing signs of heat soak and wasn’t up to the task of handling the added airflow.

Despite the poor performance of the intercooler, the final numbers were still impressive with the WRX churning out 300 whp and 306 ft-lbs of torque. Spool-up has lagged just a bit with the larger 20G, but only by 200 or so rpm. However, the increase of 78 whp and 80 tq easily makes up any lag.

But what about the mpg that the owner was so concerned about? He’s reported back and said that fuel economy did drop to 17–19 mpg, depending on his driving style. It’s hard to say if that’s the effect of the upgrade or a heavy foot, but he doesn’t feel bad at all considering all the newfound power. He also mentioned that he couldn’t really feel the increase in lag, which is a great success for this turbo since it’s so much larger than the stock unit.

Gains Made
TR TD05-20G & equal-length headers
+ 77.9 whp
+ 79.9 ft-lbs tq
Before 221.8 whp & 225.8 ft-lbs tq
After 299.7 whp & 305.7 ft-lbs tq

SOURCEBOX

Tomioka Racing
TD05-20G Turbo & Equal-length Headers
tomiokaracing.com
EDO Performance
WRX Tuning & Turbo Install
edoperformance.com