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Subaru WRX

2006 Subaru WRX

May 25, 2010
IHI VF22 Upgrade
with GrimmSpeed up-pipe

What better way to present the Subaru page than in the classic World Rally team fashion.

From experience, the 2006-2007 WRX has proven to be a great all around play toy with incredible drivability, handling, durability, and power from its 2.5 Liter 4 cylinder Boxer engine. The quick spooling low RPM power is excellent on the street, but it was time to give this car wider power band and smooth the power in the cruising area. This write-up will also include differences between the GrimmSpeed up-pipe and an easily affordable Ebay purchased up-pipe.

After looking for a turbo to satisfy Tim's request to keep some amount of low end power for road race style driving, Majestic Turbo in Waco, TX (site) was again able to provide TurboFreak.com with this IHI VF22 ball bearing turbo for a great price.

First up, a look at the VF22 turbo compared to the stock TD04L turbo.

The VF22 is said to flow 490cfm at 18 psi which is quite a leap over the stock TD04L turbo. The large P20 turbine housing (shown below) is a great increase for gains in upper RPM flow which increases horsepower capabilities. Since this turbo was installed on a 2.5 liter engine spoolup is not a problem and this engine could stand to loose a little horsepower in the low RPM range over the stocker turbo.

The power difference between the two is to be expected. The RPM band is much more broad with greater acceleration from 5000 to 6000 RPMs where before it would have a short heavy rush of torque then fall off significantly as all micro sized turbos react. The smoothness of the power and constant upper end pull completely changes the personality of this car which makes drivability much better on the highway and the city streets.
Boost control by the stock wastegate solenoid is terrible to say the least, but most normal WRX boost drop in the upper end was taken care of by alot of tuning to the wastegate table in the tune. Please also note that a hardware change, such as a larger turbo, will need to be tuned with ecu editing software. If you are in the surrounding DFW area, TurboFreak Tuning and performance mechanic service is available if you contact chris at turbofreak dot com.

Now to cover the up-pipes:

VF22 and GrimmSpeed up-pipe

Above are photos of the black heat coated GrimmSpeed up-pipe and the cheap Ebay bought up-pipe attached to the VF22 turbo. As always, I will review only facts and previous experience with similar information revealed in past research.

The Ebay pipe looks shiny and is very affordable, though the stock up-pipe specs maybe better to use for faster spool up.  Low end and upper end may both be affected by common issues which affect velocity and flow.
This is a 2.5" pipe with a 2.0" opening in the turbo flange. Instantly this creates a major flaw as exhaust flow through the pipe will hit a 1/2" wall before exiting into the turbo creating undesirable turbulence. To add to this, the opening at the turbine housing flange is 1.76" and the up-pipe's opening is 2.0" where flow will again hit a wall to cause turbulence. See photo below:

As you see, the turbine housing is intrusively hanging inside of the flow area. We must also realize the larger inner diameter pipe is so much more volume to fill before velocity of expanding exhaust gasses take effect to start the turbo spooling. 

The higher quality GrimmSpeed up-pipe is nothing like this and was chosen for this reason. All flange openings and pipe size is within spec of the stock manifold collector and turbine housing as shown below:


Overall the results of the Grimmspeed up-pipe and larger VF22 ball bearing turbo on the 2.5 liter resulted an average of .2 G's higher acceleration through the RPM band. You will find many threads on the net talking down the VF22 from individuals who seem to be looking for much higher horsepower. The facts are this turbo was very affordable to obtain, spoolup is still very good, and the customer got the power and drivability he was expecting.