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first modification thread

first mod thread also

Most Popular Uppipe Poll

Facts about the WRX stock exhaust - Thanks WRC_obssed for the link

Great page for turbo basics - Thanks AJ for the link

Spark Plug Installation

Exhaust/uppipe combo thread

Stock EGTs by cylinder [Why not to MBC or intake a stock EJ]

Modification Path
In general, please do not skip modification steps. Do not try to add a new turbo to a stock car. Get rid of the catalytic converters, get some engine management. Get the neccessary fuel mods (injectors and fuel pump size depending on needs IHI turbos are fine with STI injectors) Then get the turbo and intercooler upgrade if you feel it neccessary and install that with the fuel mods together at the same time. Then get your car on the dyno or a road tune to get the most out of your mods, as the base maps are not very good. Note: Header is not normally included here

So How Do I get rio of all the catalytic converters (there are 3)
In most cases a downpipe will eliminate both the downpipe and the midpipe cat in one piece. Very few downpipes are only the downpipes (stroumung comes to mind that is only a downpipe) So if you get a new downpipe you will have gotten rid of 2 catalytic converters, so you have one left in the uppipe. Here is a diagram of the wrx exhaust system:

All these stages say turbo back exhaust. What if I want to mix and match brands, how do I then have a turbo back exhaust?
A turbo back exhaust is just that, the exhaust from the turbo-back. (see diagram) You can still make a turboback exhaust with a catback and a downpipe. (for instance, I have a tanabe catback with an invidia downpipe)

What is a "bellmouth" downpipe
That refers to where the downpipe meets the turbo. In most cases a non bellmouth will be fine unless you plan on upgradeing your turbo.

HKS NONbellmouth Downpipe

Helix Bellmouth Downpipe

Should I get a bov?
Trailboss said:
Blow off valve on a stock engine
Cool sound

Run rich between shifts
Could cause long term engine problems
Not necessary until you're running 20+lbs of boost
Decreased gas mileage

Blow off valve on a modified engine w/ turbo upgrade
Ability to hold more boost (20+lbs)
Cool sound -- commonly reffered to as a "show off valve" :rotfl:
Give yourself some deserved bling bling for running an upgraded turbo

Still might run rich, but with engine management you could help to tune that problem out.
Still could cause long term engine problems...but when you've done everything to upgrade your turbo, you're running that risk anyway.
Decreased gas mileage - due also to added fuel (larger injectors) w/ engine management to feed the upgraded turbo more air and fuel.

Things to think about....
What Are These "stages" Everyone keeps talking about?
Most people base their stages off of Turboxs's definitions which are (
Stage 1:

Stage 2:
Turbo XS turbo back exhaust (TBE)

Stage 3:
TXS TBE, Uppipe & TMI (top mount intercooler)

Stage 4:
TXS TBE, Uppipe, STI Injectors, and walbro fuel pump, VF3X (either a vf30 or vf 34 is normally used), & TMI

TurboXS UTEC Instructions READ THEM BEFORE EVEN TOUCHING A UTEC User Manual 4.2.pdf

Cobb's stages
Stage 1- Acessport ECU
Stage 2- Acessport and turbo back exhaust
Stage 3- Under devlopment, coming out Fall 04. Though i belive they do have maps now for the vf30/vf34.

boost conversion for hkpa
14 0.966
14.25 0.98325
14.5 1.0005
14.75 1.01775
15 1.035
15.25 1.05225
15.5 1.0695
15.75 1.08675
16 1.104
16.25 1.12125
16.5 1.1385
16.75 1.15575
17 1.173
17.25 1.19025
17.5 1.2075
17.75 1.22475
18 1.242
18.25 1.25925
18.5 1.2765
18.75 1.29375
19 1.311
19.25 1.32825
19.5 1.3455
19.75 1.36275
20 1.38

IHI turbos from

This turbo has the highest output potential of all of the IHI VF series turbos and is the best choice for those who are looking for loads of top end power. The top end power however, does not come without a cost. The VF22 spools significantly slower than the rest of the IHI models due to the larger P20 exhaust housing and is much less suited for daily driving than some of the other models. Although the largest VF series turbo, the VF22 is not quite optimal for stroked engines or those who wish to run more than 20PSI of boost. The VF22 is best mated with the 2.0 block and in applications of 20lbs of boost or less.

The VF30 is commonly considered the best bang for the buck turbo in the IHI VF series line. A relatively new model the VF30 features the the same exhaust housing as the VF24 but a larger compressor side similar to the VF22. The combination of these two parts results in increased output potential without the lag associated with the VF22. Although it doesn't offer the top end supremecy of the VF22, the VF30 is a great compromise between these unit and the quicker spooling models.

The VF34 is nearly identical to the VF30, with the same exhaust housing and compressor. However the VF34 goes back to the ball bearing design, and in doing so achieves full boost approximately 500RPM sooner than the comparable VF30. The VF34 is the most recent IHI design and as such costs slightly more than its counterpart. Top end performance and maximum output are identical to the 30.

Provided by Dark Rex (*Information was derived from many sources including NASIOC, MRT website, PPMotorsports website,,, WorldOne and Rallispec website.)

This turbo is considered a great all-around turbo. Like the VF22 it utilizes the largest P20 exhaust housing. This housing is mated with a smaller compressor housing of the of the VF24 for fast response and excellent low and mid-range performance. It does not have the same top end power of the VF22, but spools up significantly quicker. Standard ball bearing center section. Excellent bolt-on replacement for the standard WRX turbo on cars without any other major modifications. Expect flows around 430 CFM at 18 PSI.

This turbo shares its compressor housing with the VF23 however, this housing is mated with a smaller (P18) exhaust side. The smaller characteristics of this turbo allow it to provide ample bottom end power and quick spool. This turbo is very popular for Imprezas with automatic transmissions and Group N rally cars. Not recommended for stroker engines or engines with high boost as turbo is small and can over speed. Best turbo for cars that want the best bottom end and least lag. Expect flows around 425 CFM at 18 PSI

This turbo came standard on the STi Version 5. In terms of overall size, it is smaller than the VF22, VF30 and VF34, and about same size as the VF23. Expect flows around 425 CFM at 18 PSI

This Turbo is nearly identical to the VF24, with the same compressor and exhaust housings. However the compressor wheel in the VF29 is has been changed slightly. The changes made to the compressor wheel in this model are generally viewed as improvements, and as such this unit is typically chosen over the VF24. Has a different location for the pressure hose on the waste gate actuator Expect flows around 425 CFM at 18 PSI

The VF35 utilizes the same compressor housing as the VF34 however it also features a divided thrust or offset ball bearing design. The smaller P15 exhaust housing for quicker spool up and a slightly more limited top end. The compressor inducer size is the same as a VF30/or 34 turbocharger.

VF35Thread Discussion

VF22 Vs 18g

VF34 Vs VF22

18g thread with more results within

daily driven turbo discussion

VF34 VS 18g

maybe ill add more later, but this should be plenty to get you started. enjoy

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