Power Train

afe Series Turbo

Compressor & Turbine Sections

Gaese & Fresh Air Flow Chart

Turbo Chargers

Bigger, Badder, and Pumping Up the Pressure.

After the "basics" of better airflow (exhaust, intake, etc.) and baseline engine management, the next step is to take the plunge with a larger turbo. The base turbo is a Mitsubishi TD04. Originally, when the WRX first debut in 94, the WRX came with a larger Mitsubishi TD05 turbo. The larger turbo allowed for greater top end horsepower at the expense of turbo lag and initial spool up. Thus, starting in 97 Subaru replaced the TD05 in favor of the smaller and quicker spooling TD04.

So?where to begin and what type of turbo to install? Well, for starters, look to Subaru's own in house performance tuning division - STi. The 280 hp WRX STi V7 sports an IHI VF24 roller ball bearing turbo.

Roller bearing turbos give you fast transient spool up - full boost comes on quickly.

Remember, to take full advantage of a new turbo, you must run some sort of enginemanagement. Also remember that when you surpass the 325-330 hp mark, the stock fuel system becomes inadequate. (read: the fuel injectors and fuel pump can't supply enough fuel to run safely)

IHI turbo - (See table for Turbo Specs)

The VF series (VF22, VF23, VF24, VF29, VF30, VF34, VF39) are the most common direct replacement turbos. All VF-series turbochargers use the same roller bearing, water-cooled core assembly. The differences are in their wheels and housings to achieve different flows.

The VF22 has the largest potential for peak horsepower. In other words, in the IHI model range, the VF 22 supports the highest boost levels. It is capable of running up to 25 psi. Because it is a roller bearing turbo, turbo lag is minimal...the boost comes on around 3300 rpm. Expect to max out the VF22 somewhere in the 400-450 hp range.

The VF23 starts the middle ground. It comes on boost around 3100 rpm and is capable of running 20 psi of boost. Expect to max out the VF23 somewhere in the 300-350 hp range.

The VF 24 starts to come on around 2900 rpm and will significantly improve power through the midrange over the stock TD04 turbo. However, the VF 24 is only capable of running around 17 psi.

The VF23 and VF 24 are a great replacement for those who value drivability higher than maximum power.

The VF29 & VF30 delivers a very wide increase in torque over the standard TD-series turbos.

The VF 30 is a fairly new IHI model that utilizes the exhaust housing of a VF24 and the compressor housing sized between a VF 23 and a VF 22. It comes on boost down low (around the 3000 rpm range). With upgraded injectors, fuel pump, and engine management, the VF 30 is good for 365-390 horsepower. It is important to note that the VF30 is NOT a roller bearing turbo.

The IHI VF34 (which comes standard in the Japanese market STi version "RA") is a new roller bearing turbo. It has the same specifications (compressor size, etc.) as the VF 30. The difference lies in the roller bearing which, theoretically, allows quicker spool and better response. It costs a couple hundres more than a VF 30. The VF 34 maxes out around 365-390 hp. It is probably the most popular option for big turbos on the WRX.

One other turbo to note is the VF comes standard in the USDM STi. While we don't have all the specs yet, these are a new roller bearing, TWIN SCROLL design. Performance numbers are pretty similar to the VF34...maxing out just under 400 hp.

A new high performance modified IHI turbo has made its way to the market recently. They are the Power Enterprises PE 1818 and the 1820. The 1818 supposedly comes on boost extremely fast...which make it great for road racing or aggressive driving (remember to be responsible :^). The 1818 maxes out somewhere between 350-375 hp.

The 1820 is larger than the 1818 and is capable of running more boost, but at the expense of more turbo lag. Expect it not attain full boost until you have passed 4000 rpm. However, it can be tuned to 400+ hp.


Advanced Vehicle Operations (AVO Turboworld) offer several sizes of bolt-on turbocharger upgrades. AVO's turbos also have a roller bearing centre as well as a high-efficiency split-pulse hi-temp turbine housing. Using an identical centre section, these turbochargers come in 320, 400 and 450hp configurations to cover all applications.


Other manufactures include Garrett's A032 as well as other modified Garrett turbochargers from various turbo specialists like XS Engineering. The Garrett turbos seem best suited to making huge power gains (read 400+ hp) at the expense of turbo-lag. Most of these turbos seem to come on full boost between 4000-5000 rpm.

IHI & Garret Turbo Specs

Compressor Inlet Diameter
Compressor Housing Nominal
Turbine Housing
Approx A/R
Compressor Wheel Blades
Turbine Wheel Blades
Waste Gate Actuator
Turbine Casting ID & Batch
VF22 Roller Bearing
9.4 PZ20-H
C395 H, H4
VF 23 Roller Bearing
9.4 PZ20-H
C395 8psi TBA
VF 24 Roller Bearing
9.4 PZ18-H
C418 8psi H, S4, 66
VF 30 Bronze Bearing
9.4 PZ18-H
C484 H, S4, IC F55
VF 34 Roller Bearing                  
Garrett 400 Ball Bearing 53 - - Outlet Dia 51.5 - 7 9 11 psi  
Garrett 450-500 Ball Bearing 53     Outlet Dia 46.9 - 7 10 14 psi  






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