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Kobiyashi 01-15-2004 10:03 PM

_THE_ WRX Modification Guide *Complete*
*** This guide was written in my opinion and I am not responsible for any damages caused by following it, nor am I responsible for any legal repercussions of following this guide. After 10 private messages, 20 instant messages, and many phone calls a day; I have decided to write a modification guide that should help most WRX newbies (and other owners) with questions they have about modification. If you notice something missing, or require an addition; please email [email][/email]***

1.0 Intro

1.1 -Intro To Tuning

1.2 -Common Mistakes
1.21 -Raising Boost Prematurely
1.22 -Installing An Intake Prematurely
1.23 -Voiding Your Warranty
1.24 -Soft Break In

1.3 -The Order

2.0 Engine Performance

2.1 Engine Management
2.11 -Programmable
2.12 -Constant

2.2 Gauges
2.21 -A/F Ratio
2.22 -EGT
2.23 -Boost
2.24 -Others

2.3 Exhaust
2.31 -Downpipe
2.32 -Midpipe
2.33 -Uppipe
2.34 -Headers
2.35 -Muffler

2.4 Boost Controllers
2.41 -MBC
2.42 -EBC

2.5 Intake
2.51 -Short Ram
2.52 -Cold Air

2.6 Fuel System
2.61 -Injectors
2.62 -Plugs
2.63 -Pumps
2.64 -Regulators
2.65 -Rails

2.7 Intercoolers
2.71 -Front Mount
2.72 -Top Mount

2.8 Turbo Chargers
2.81 -IHI VF22
2.82 -IHI VF23
2.83 -IHI VF30
2.84 -IHI VF34

2.9 Misc.
2.91 -Blow Off Valve
2.92 -Turbo Timers

3.0 Transmission
3.1 STI 6 Speed

4.0 Suspension
4.1 Springs
4.2 Shocks
4.3 Strut Tower Braces
4.4 Sway Bars
4.5 Coilovers
4.6 Anti-Lift

|1.0| INTRO

This Guide is by no means completed or even started. I decided to post this guide and update throughout the next few days so that people can enjoy the information provided before I finish the entire paper.

|_____1.1 - INTRO TO TUNING

Tuning the WRX is like tuning any other car. It is nothing you should rush into. You should look at all your options and know exactly what you are doing. If you think tuning your WRX is something that will not require maintenance or time, you should look to a new hobby. I have been tuning for over 6 years and still find it takes a lot of my time. If you are married I would seriously talk to your spouse before you start working on your car, make sure that it is something that is ok with the both of. Many fights in my life and friends around me have happened within there marriage because of this. With that out of the way, if you are somebody that has the time, energy, and money to spend on this hobby I hope this guide helps you.


Many people rush into tuning a car before understanding how the car works. I would recommend you purchase “Training WRX” by Nick Warne if you are serious about tuning your car


People rushing for speed raise boost right away to gain 20, 30, even 40 horsepower. This is extreme dangerous and could lead to serious damage to your turbo and even your engine. There is a Catalytic converter 3” away from your turbo in your Uppipe (See Exhaust for diagram) that could dislodge comb into your turbo charger, costing you upward of $2000.00 to replace. I can’t stress this enough, 40 hp for free sounds great, but that for that price if something should happen, do NOT raise your boost levels until that Uppipe is replaced.


I fully understand the reasoning behind this mod in some WRX owner’s eyes. In most other cars a good Intake is worth 5 to 10 hp, however not so in the WRX. It does change the turbo spool sound to add a quite nice scream at full boost, however can potentially damage your engine, not to mention little to no power gain. The stock intake (minus the resonator, See Exhaust for diagram) is capable of 325 hp. Intakes simply lean your car out (More Air Less Fuel) to gain power and can seriously hurt your engine and turbo if installed before engine management and injector upgrades.


If you want to keep your car under warranty I would not recommend tuning at all. You can contract your dealer and find out what mods are acceptable, however even then risk the change of coverage. The best policy to assume is that if the car isn’t stock, it’s not covered. A simple Blow Off Valve can void your entire engine at some dealers.

|_____1.24 - SOFT BREAK IN

Oh no! He didn’t just say what I thought he said, did he? Yes I did. A highly debated decision even among professionals, should I baby my car at first or let it have it? The correct answer lies in the middle. So what’s the best way to break in an engine? Run it hard. Why? Nowadays, the piston ring seal is really what the break in process is all about. Contrary to popular belief, piston rings don’t seal the combustion pressure by spring tension. Ring tension is necessary only to scrape the oil to prevent it from entering the combustion chamber. If you think about it, the ring exerts maybe 5-10 lbs of spring tension against the cylinder wall … How can such a small amount of spring tension seal against thousands of PSI of combustion pressure?? It Can’t. So how do rings seal against tremendous combustion pressure? From the actual gas pressure itself! It passes over the top of the ring, and gets behind it to force it outward against the cylinder wall. The problem is that new rings are far from perfect and they must be worn in quite a bit in order to completely seal all the way around the bore. If the gas pressure is strong enough during the engine’s first miles of operation (WIDE OPEN), then the entire ring will wear into the cylinder surface, to seal the combustion pressure as well as possible. So what’s the problem with easy break ins? … The honed crosshatch pattern in the cylinder bore acts like a file to allow the rings to wear. The rings quickly wear down to peaks of this roughness, regardless of how hard the engine is run. In fact, if the rings aren’t sealed properly within the first 50 miles they will never be. Most engine problems are caused by two things in later engine life, not allowing the engine to warm up completely before running it, and easy break ins, either case is easily avoided. Oh no, I’ve already broken the car softly what can I do? First off, chances are you gunned it for that test drive at least once or twice (which is great to do) but if not, don’t worry. Horsepower loose on a fully tuned WRX is around 4% due to improperly set rings. The only real way to correct it is to reinstall rings, but isn’t worth the hassle unless you are an active rally or track racer. Just keep an eye on those rings into the higher mileage.

|_____1.3 - THE ORDER

I lot of people have asked for my recommended order of upgrades and mods. For now I am just compiling a list for engine performance. For more details on any step please view the specific section for the upgrade.

A. Exhaust ([catless]Downpipe, Midpipe, Muffler, and [catless]Uppipe) +10 HP
B. Turbo Timer +Save Your Turbo HP
C. Gauges (EGT, AFR, and Boost at the minimum) +Save Your Engine HP
D. Engine Management (Timing, Fuel, Boost) +40-60 HP
E. Fuel System Upgrade (Injectors, Pump, Rail, Regulator, and Plugs) +10 HP
F. Intake +5 HP
G. Clutch and Flywheel +Needed To Handle Next 2 Upgrades
H. Intercooler +20-30 HP
I. Turbo +40-150 HP

That is just a quick overview of what order mods should be done (IMO) to safely increase power in your WRX. These mods should not be done hastily or without care, and are listed in simple order just for an overview.


As most of you could guess, power comes from the engine. Getting reliable power out of the EJ20 isn’t hard at all as long as you follow proper safety guides and know what you are doing.


Engine management is divided into two parts. Programmable (Able to be changed by user) or Constant (ECU flashes which are done by tuning shops) Again this is a personal preference area, however if you heavily modding your WRX often, I would recommend getting a programmable Engine Management that includes your Fuel, Timing, and Boost.

|_____2.11 - PROGRAMMABLE

The best choice for WRX enthusiasts that will be modding their car regularly. I personally recommend the TurboXS ([url][/url]) UTEC. It controls fuel, timing, boost, as well as many other additional features; that can be changed on the fly via a PDA or laptop. I choose this simply because it is all-inclusive, you really won’t need any other fuel controllers or boost controllers. Some people like to have separate controllers for boost and fuel, however the problem is; the only way your going to control timing is through the ECU, which leads you back to some sort of UTEC or Flash. Why not skip the other management products and go right to timing, which includes everything?

|_____2.12 - CONSTANT

Constant engine management is mainly set up for timing and fuel. This is for somebody who doesn’t change mods much and wants to control boost using an outside device (GReedy Pro. B). This would involve getting your ECU flashed at a tuning shop, which no hopes of quickly changing it, or going back to stock to trouble shoot. I personally would recommend staying away from such an engine management unless you are done modding your car.

|_____2.2 - GAUGES

Gauges are a must. Would you bake something without seeing the temperature on the oven? I don’t think so; so while do something with you car without seeing what it is doing also?

|_____2.21 - A/F RATIO

An Air to Fuel Ratio gauge, a.k.a. AFR gauge, reads the ratio of air to fuel in your engine. You want your ratio of air to fuel to be lower (richer, more gas less air) under throttle than not. Anything under a ratio for 12.5:1 is considered rich by a stock WRX due to its limited reading without a wideband sensor. Most people simply quote the first number in the AFR reading, since the last number is always one, 12.5 AFR reading. I recommend installing a wideband sensor to find these readings below 12.5 if you are seriously modding your car. AFR can be used to lower the temperature in your exhaust gases also by adding more fuel to the mixture, as well as removing fuel to create more horsepower. As for which sensors and gauges to use, no one company can be considered the best and is up to personal preference.

|_____2.22 - EGT

EGT, or Exhaust Gas Temperature, is used to measure just that; how hot your exhaust gases are. This is used for tuning anything on your car. EGTs that are to hot can damage your car and cause knock, while to cool of EGTs (never seen on a modded car) can lower turbo performance. Most people consider 1600-1650 degrees Fahrenheit to be the threshold between ok and damaging. The problem with just installing a gauge is found when we look at the placement of the stock EGT probe, in the Uppipe. This is a bad place for any temperature readings due to its distance from the engine, and more importantly its distance from the infamous lean cylinder #3. Almost agreed upon by all WRX tuners, a probe should be placed in the manifold or headers at that cylinder.

|_____2.23 - BOOST

But I already have a stock boost gauge, why do I need to read this? Most importantly, because the stock boost gauge is often inaccurate at higher boost readings. So you mean I have to get a new boost gauge? Yes. I often recommend getting the Blitz Dual Turbo Timer (DTT) to kill two birds with one stone, however any other gauge company (Autometer and GReedy most notably) create very accurate gauges to be used with tuning. The easiest way to tap into the vacuum lines is right before the blow off valve (and is where the stock boost gauge is tied in at also), however, if you are installing a new gauge and had the stock gauge installed already, simply tap into that line under the steering column.

|_____2.24 - OTHERS

What other gauges are there? TONS! If you are an avid fan of gauges and can never be to careful you can look into other gauges as well as the ones I recommend to begin with. They include but are not limited to: Coolant Temperature, Fuel Pressure, Oil Temperature, Oil Pressure, and many more.

|_____2.3 - EXHAUST

The bread and butter of your WRX mods, seconded only to engine management in total HP gains due to an upgrade. Note that the Exhaust doesn’t give much HP, but it allows for a larger turbo and higher-grade gas.


|_____2.31 - DOWNPIPE

The second most poorly designed piece of equipment in your car, lead only by your Uppipe, which Subaru thought it would be a great idea to place a catalytic converter 2 ½” from your turbo. The Downpipe not only has a cat in it, it also blocks half the wastegate with a plate. That’s right, a plate, which leads to massive air flow turbulence, blocks half of your turbo outlet. I would recommend switching this with any 4” Downpipe. Some people like the separated wastegate while some argue the open pipe leads to better airflow. I for one, can’t notice a difference between the two, and would tend to say either will work fine as long as the cat is removed.

|_____2.32 - MIDPIPE

The stock Midpipe isn’t a horrible design, however you could benefit from a 3” pipe here. I for one would recommend you remove cat in this section as well if your car is for racing only. Please note it is illegal to run a car without cats for on-road use. (My lawyer made me). Keeping this cat would not hurt your performance greatly, but wouldn’t allow you to easily run higher-grade gasoline. You will also find your rear O2 sensor located here, which will be useless if you upgrade your cat, and you would need to place a resistor in the line to block from bad readings.

|_____2.33 - UPPIPE

THE MOST POORLY DESIGNED PIECE OF EQUIPMENT ON YOUR CAR, Subaru thought it would great to place a cat 2 ½” from your turbo charger, ON THE INTAKE SIDE! Replace this before you even think about raising your boost. I would recommend any Uppipe without a cat, which ID equals the same as the turbo inlet. Any larger and you disrupt the airflow and loose power instead of gain from the larger pipe. This pipe also has an EGT probe in it, which is a very bad placement. I would recommend mounting a bung right outside Cylinder #3 on the headers.

|_____2.34 - HEADERS

The stock headers perform fine under normal tuning, however if you are going to upgrade to a larger turbo you will find that 4 to 1 headers will greatly increase your spool time and peak boost. Headers vary a lot and should be compared before purchase. I would also recommend buying a set that includes your Uppipe (so you know they will fit fine) if you have the available funds to do so. The headers hold your front O2 sensor and should also hold your EGT probe outside Cylinder #3.

|_____2.35 - MUFFLER

This is purely up to preference, and doesn’t show any largely noted HP increase. Some people argue that 2 ½” is fine, while others say you should continue with 3”. I haven’t felt a real HP difference in anything setup, and would recommend going with the one you enjoy the sound of the most.


Boost controllers only apply to people who are not running boost through their engine management.

|_____2.41 - MBC

The MBC or Manual Boost Controller controls boost by placing a restriction between the line that runs from the wastegate actuator to the turbo. This is adjusted by turning a bolt inside the valve in the engine bay and cannot be set to change boost throughout gear and rpm ranges. I would not recommend this to any persons wanting to keep boost above 15 lbs. 15lbs is dangerous at redline without heavy modding and shouldn’t be done by a novice.

|_____2.42 - EBC

The EBC or Electronic Boost Controller controls boost by either the boost control solenoid already found in your car, such as engine management, or by electronically adjusting the restriction on the line between the wastegate actuator and the turbo. Some are a simple one setting controller, which I would not recommend for running over 15lbs. While others, such as engine management, can change with RPM and throttle settings.

|_____2.5 - INTAKE

As previously noted, any novice should not upgrade this until your Engine management and fuel system are able to handle it.

|_____2.51 - SHORT RAM

This intake is simply attached off your turbo inlet in your engine bay. A short piece of pipe is then connected to a cone filter where the old intake filter used to be. This intake allows for maximum airflow, but delivers hotter air. This intake is also not as likely to dangerously lean your car out without you knowing it. A Short Ram is also required for anybody running a FMIC, as the side wells will be consumed by the piping.

|_____2.52 - COLD AIR

This intake is attached off your turbo inlet in your engine bay and run down into your tire well. This is done to bring the cold air from outside the engine bay into your intake, thus increasing density charge. It has been noted however, that this intake is known for leaning your car out and does not provide the results, as one would expect, to your boost and overall horsepower rating.

|_____2.6 - FUEL SYSTEM

The stock fuel system in your WRX is good till 325 HP or so. After that you will need to upgrade your injectors, rail, and pump at the very minimum.

|_____2.61 - INJECTORS

The injectors on your WRX should be the first things you upgrade. Anything over 500cc will be fine, unless you are planning on running an extremely large turbo charger and nitrous, at which point I would install 800cc injectors. New injectors will work ok with the stock fuel pump, however I would also recommend upgrading that at the same time.

|_____2.62 - PLUGS

Upgrading your spark plugs is a very easy way to lower engine temperatures. Simply install a plug with a higher heat rating (7 recommended). I would also recommend letting a Mechanic install your plugs unless you have a complete tool set and a good two or three hours the first time you do them.

|_____2.63 - PUMP

Your stock fuel pump is only good for so much fuel delivery and should be upgraded to a 255ltr fuel pump if you plan on upgrading your turbo at all. I would also consider installing a new regulator to maintain good pressure with the new pump.

|_____2.64 - REGULATOR

Although not required, I would recommend install a new fuel pressure regulator if you install a new fuel pump. This could save you many problems down the road.

|_____2.65 - RAILS

Fuel Rails should be upgraded if you raise boost at all if you want to see your engine into the 100,000-mile mark. Cylinder #3 runs extremely lean, and hotter than the rest. Even if no detonation is occurring it is still putting undue wear on this cylinder.

|_____2.7 - INTERCOOLERS

If you are planning on upgrading your turbo, you must upgrade your intercooler. There are two ways to do this, one being Top Mount, the other, Front Mount. Both have advantages and disadvantages.

|_____2.71 - FRONT MOUNT

A front mount intercooler, or FMIC, has the best density charge and cooling capacity, however due to its length away from the turbo charger, will create more turbo lag (spooling time for the turbo) than a Top Mount. A FMIC is however required to achieve higher top-end boost as well as for the larger turbo chargers such as the IHI VF22. I would also recommend a FMIC for the IHI VF23, however it is not required. If you want more boost and power, yet lower end lag, go with the FMIC, if you want instant power, yet not as strong, please read the Top Mount Intercooler listed below.

|_____2.72 - TOP MOUNT

A top mount intercooler, or TMIC, has the least amount of turbo lag and is best used with smaller turbo chargers to create large amounts of low-end power. However, not as powerful as the FMIC at the top-end, it stands its ground being able to push upwards of 400 HP, while allowing full turbo spool in most turbo at or below 3000 RPM. I would recommend a TMIC with the IHI VF30 or VF34.

|_____2.8 - TURBO CHARGERS

This is why you have your car right? It’s turbo charged, it sounds nice, it gets stares as your BOV, or Blow Off Valve, echoes across the parking lot. Sure it is, you don’t need to deny it. If your cars parts were label this would have the GO BABY GO sticker on it. Turbo charges are very powerful, yet fragile as well. You should also think long and hard on how you want your car to perform before you purchase a new turbo charger, as well as what kind of Intercooler you have installed. Some turbos are great for high-end boost yet do not achieve max boost until much later than the smaller turbos. Please note, I only cover IHI turbo chargers in this section for I have not been able to work hands on with any other major brands.

|_____2.81 - IHI VF22

This is a popular replacement turbo for WRX’s with heavy modifications, such as exhaust and front mount intercooler, kits, 4 to 1 headers, etc. (designed for greater blow) as this turbo will start to come on boost at 3300 rpm, however is capable of running up to 25 psi @7000 rpm for over 500HP.

|_____2.82 - IHI VF23

This is the other popular replacement turbo for WRX’s heavy modifications, such as exhaust and front mount intercooler, kits, 4 to 1 header, etc. yet can still be run with a TMIC and has considerably less turbo lag than the VF22 as this turbo will start to come on boost at 3000 rpm, and by 3200 rpm is capable of 20 psi @7000 rpm for over 450HP.

|_____2.83 - IHI VF30

The VF30 has a bigger compressor than the VF23 at 47mm. It incorporates a 9 blade compressor wheel. The core is a divided thrust bearing and has a P18 exhaust housing. This is the standard turbo on the New Age Sti and has better spool times than the VF23 as this turbo will start to come on boost at 2900, and by 3300 rpm is capable of 19 psi @7000 for around 400HP.

|_____2.84 - IHI VF34

The VF34 is similar to the VF30 but has improved spool up due to roller bearing design as this turbo will start to come on boost at 2700, and by 3000 rpm is capable of 18.5 psi @7000 for around 390HP.

|_____2.9 - MISC

Two other items that were mentioned but not covered in detail I should address.

|_____2.91 - BLOW OFF VALVE

I’ve heard both sides of the story to this component. Stock is fine vs. Upgrade to an External venting. In either case, they are incorrect; the stock BOV is only good till 19 to 20 psi (in some cases even less) and an external venting BOV has no better performance than a recirculatative. I do recommend upgrading the BOV if you plan on running an aftermarket turbo charger, or if you wish to simply hear it vent pressure. Nothing says you have a turbo changer like a loud BOV.

|_____2.92 - TURBO TIMER

As discussed in the earlier parts of this document, a turbo timer is a MUST! As to which turbo timer, that is up to personal preference on many levels. I would make sure that it reads your boost as to set the ignition disconnect delay according the turbo use as well as purchase a wiring harness made to fit your WRX.


The gears that transmit power from an automobile engine via the driveshaft to the live axle. That’s great an all, but the real question is, “Is stock ok?” For most people that are lightly modding their WRX the stock transmission is great. I wouldn’t recommend running several drag runs on the stock, or launch at 6,000 RPM; but for everyday use up to 400HP+ the stock transmission should be fine without abuse. I would further discuss upgrades in the section, however choices are very limited without extreme modification.

|_____3.1 - STI 6 SPEED

The most common is to replace with the STI 6 speed transmission which can installed with minimal hassle, but rather large expense ($5500 on average, total). This transmission can handle anything you throw at it though (save again, redline drops) and corrects the weak second gear.


Whether you are a rally fan, or a road racer, suspension is a must. Hard, soft, lower, high, it’s up to you. I will go over the basic parts involved in making your WRX handle like a dream.

|_____4.1 -SPRINGS

1” or 4” ground clearance is up to you. Springs can be used to adjust the ride height of your WRX as well as the stiffness. This is a must upgrade from stock either way. If you are lowering I would recommend purchasing a spring that lowers the front considerably more than the rear due to the finder gap. However, upgrading springs should not be done without upgrading shocks, as the new springs will put more work on the already weak stock shocks.

|_____4.2 - SHOCKS

Shocks improve ride quality as well as control. This is what makes your car stiff to the road. Good racing shocks should be installed for rally, track, and drag. All three will notice the launch and racing difference with upgraded shocks. For serious rally and track racers I would recommend purchasing adjustable shocks for customizable uses.


Drag Racers bug out! This is for you rally and track fans. Hate that body roll, which your car would turn stiffer, then this is your answer. Relatively cheap compared to most suspension upgrades this by far adds the most support to turning and body roll. A must have!

|_____4.4 - SWAY BARS

Didn’t I tell you drag fans to get lost? Want proper chassis balance and improved steering response? This is for you. Just like the tower braces above, these greatly improve the rigidness of your WRX. With all sway bar installation I recommend new end links as well, a simple but helpful addition when running performance sway bars.

|_____4.5 - COILOVERS

Rally Fans ONLY please. When you need the ultimate suspension, this is for you. Extremely expensive for most casual tuners; however invaluable to racers. Most coilovers require a purchase of additional upper strut mounts, but few can be found direct bolt on. A must have for various track conditions.

|_____4.6 - ANTI-LIFT

Ok Drag fans, you’re safe again. An often-overlooked part of suspension upgrades (which could almost be added to performance upgrades) is an Anti-Lift kit or Steering Response Kit. I swear by these for launch control and acceleration stability. I’ve never seen somebody install one and wish they hadn’t. Even cornering, this removes a large amount of body movement.


I do apologize for the great delay of the completion of this guide; but alas here it is. If you have any questions, requests, or comments please send them to [email][/email] or give me a call anytime ([url]

Insanity leads to chaos
Then to solitude
The fruitless effort of adding
Meaning to what is meaningless
A lone, crimson tear
Falls to the sea...
The echo of the remaining star
Cries out in the infinite vacuum
The least I can do
Is send my distant prayers
Over the wind of time,
Setting sail on dreams...


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