Category Archives: Subaru

Spark Plug info for your Subaru WRX/STi:

Spark Plug info for your Subaru WRX/STi:

Refer to your owners manual for recommendations. Alternately, you can visit an auto parts store or online retailer for recommendations on suitable spark plugs designed for your vehicle. Major manufacturers are:
a. NGK
b. Bosch
c. Denso
d. Autolite
e. Champion

Sti spark plug location
STi spark plug location

Who are the specialty spark plug manufacturers? These manufacturers make specialty plugs that have unique compositions or designs that claim increases over traditional plugs. They are listed for advanced users or those with interest.
a. Torquemaster
b. Beru (specifically the Silverstones found here)
c. SplitFire
d. PREP spark plugs
e. E3 spark plugs
f. Pulstar plugs

What types are there? There are really three main types:
a. conventional nickel alloy (commonly referred to as “copper”)
b. platinum
c. iridium

Which type should I use? That depends on how often you are interested in changing the spark plugs. Conventional spark plugs generally last one year. Platinum or iridium can last, depending on manufacturer specifications, up to seven years.

What’s some good background spark plug information?

Materials: The three main types of spark plug materials are nickel alloy, iridium, and platinum. Copper can be used in the core all plugs.

All ground electrodes are made of nickel. The use of Platinum and Iridium, which are stronger, allow for much finer CENTER electrodes (the ground electrode is still Nickel). These finer electrodes do not quench the flame core as much as a conventional style plug. This increases ignitability, therefore increasing HP. It’s not a huge gain, but cylinder pressures are measurably higher.

Platinum or iridium can be used as a thin pad which is laser welded on the ground electrode (the “J” strap), this serves to increase the life of the plug.

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Pulley Subaru WRX/STi Rundown

The primary purpose of an aftermarket pulley is to reduce the size and/or mass of the stock unit. They serve two purposes: to reduce horsepower loss and increase throttle response. Notice the use of “reduce horsepower loss”. Pulleys DO NOT add horsepower, rather they free up horsepower due to the reduction of rotational mass.


Grimmspeed Lightweight Crank Pulley Black – Subaru All EJ Engines

A lightweight aftermarket perrin pulley.
A lightweight aftermarket perrin pulley.

HP gain is 5-10HP. These HP figures are a range as there have been very few before/after dyno runs with lightened or under driven pulleys.

What is a lightened pulley? Generally, it is an exact copy of the OEM pulley only CNC machined out of aircraft grade aluminum and powder coated for corrosion protection and aesthetic appeal.

What is an under driven pulley? This is a pulley that mimics the function of the OEM unit, but is smaller in diameter. This will reduce the duty cycle of the pulley and proportionally the parasitic drag on the engine.

Are under driven pulleys bad? It depends on the amount they are under driven. Some under driven pulleys can lead to reduced A/C output, lighting problems, stereo problems, and other voltage issues. Some are lightly under driven and some more so.

Isn’t replacing the stock harmonic damper (pulley) bad? Subarus do not come with a harmonic damper or balancer like some other vehicles do. For other manufacturers’ vehicles, this is a legitimate concern. Proof:

“Thank you for your patience as I checked with our Technical Services Department regarding your message below. They advised that the crank pulley is a pulley and nothing else. It is not used as a harmonic damper/balancer.

Thanks for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again.”

Best wishes,

John J. Mergen
Customer Service Department
Subaru of America, Inc.

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Prodrive GC8 WRX Special Editions

22B “Type UK”

In late 1998, Subaru UK officially imported 16 22Bs (described below), and passed them on to Prodrive for modification. The UK cars differ from the privately imported 22Bs, not just in their 3 year factory warranty, but with revised gear ratios more suited to UK roads.

This was achieved by changing the final drive ratio from 3.9 to 4.44 to lengthen the gearing. Cosmetically, the car got the headlights from the ‘99 model, UK rear light clusters and driving lights (not fog lights!) were fitted where the normal 22B has blanking plates. From the back, you can tell you’re looking at one of the rarest cars in the world by the “Type UK” and “Prodrive” stickers. The price was £39,950, and demand for the cars was overwhelming.

The rear of a Prodrive 22B Type UK.
The rear of a Prodrive 22B Type UK.

Interestingly, Subaru UK were not able to put their 16 cars through the Single Vehicle Approval scheme because the maximum of 50 privately imported 22Bs had already been registered in 1998. Consequently the Type UKs were registered in 1999. The cars do not meet European Type Approval regulations for noise and emissions.

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Turbocharger: How to choose a Turbocharger

Turbocharger: How to choose a Turbocharger for your Turbo Subaru:

In order to make an informed decision when purchasing an aftermarket turbocharger, the consumer needs to avail themselves of the different types of turbochargers first. To this end, we will discuss the various types of turbos on the market. These are just the basics of turbo information though. Please do not confuse this as the main source for turbo information as there are many other factors to an informed turbo choice such as compressor maps, matching the turbo to your displacement, etc. For the best advice, please consult an experienced turbo vendor and/or your tuner.

A regular turbo is, in essence, a pump that forces air into your intake system. The end result is a denser air charge that will produce more power vs. naturally aspired vehicles. The only downside is that more power produces more heat, and the engine’s internal components must be properly suited towards turbo charging. Upgrading this unit to a larger one is the easiest route in terms of time, trouble, and expense. Common upgrades for all turbocharged Subaru models include the VF-30/34/22 and 16/18/20G.

A twin scroll turbo is designed to be used on an equal length exhaust set-up. By internal turbo design and having all the exhaust gases enter the turbo at the same time, this allows the turbo to spool faster vs. an equally sized regular turbo. This is a very important point as many people are confused by the marketing hype of twin scroll set-ups. When comparing a twin scroll turbo that will flow say 500 cfm vs. a normal 500 cfm turbo, the twin scroll should see full boost sooner. So if there are two suitably sized turbochargers, with one being twin scroll and one regular, the twin scroll unit may be your best choice if you do not mind the extra exhaust expense and prefer faster spooling.

This type of turbocharger requires more expense than a simple upgrade though. The biggest concern is the use of an equal length header, proper uppipe design, and the possible use of a different oil pan to accommodate the new twin scroll exhaust piping. Quirt Crawford of Crawford Performance recently did some testing on a GT32 twin scroll turbo Legacy to test the theory about the importance of exhaust flow to a twin scroll unit. When he switched from the correct equal length header and uppipe to a traditional unequal length header and normal uppipe, he saw degradation in turbo response by 750 RPM. This should be word to the wise to anyone who thinks they can avoid the expense of the correct exhaust components and still see the quicker spooling benefits of a twin scroll turbo.

Another consideration is the change in exhaust tone. An equal length header required in a twin scroll set-up sounds entirely different than an OEM or aftermarket unequal length header. To fans of the familiar boxer rumble, equal length headers are just not an option. It may sound silly, but for many, this reason alone is enough to keep them from buying a twin scroll turbo.

A rotated mount turbo is any turbo that’s physical size prevents it from fitting in the stock location and must be mounted at a slightly different angle. Most of the turbos that fall into this category are of the larger variety. Many require custom piping, a front mount intercooler, external wastegates, custom tuning, tumble generator valve deletes, and other technical or expensive upgrades to support it. Most would consider this type of turbo to be outside the scope of the average do it yourself person and should be farmed out to a professional or at least utilize one of the kits supplied by various manufacturers.

As well, many feel that when going this route, strong consideration should be given to fully built motor, or at the very least, forged pistons. Rotated mount turbos produce large amounts of power and though there is no magic horsepower number for switching to forged internals, the larger rotated mount set-ups seem to be commonly used on built motors.

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Header Aftermarket Turbo Subaru FAQ

Header Aftermarket Turbo Subaru FAQ

The primary purpose of an aftermarket header on a turbocharged Subaru is to remove or replace the stock exhaust manifold with a better flowing unit.

An Agency Power Stainless Steel Header for a EJ257
An Agency Power Stainless Steel Header for a EJ257.

HP gain is 15HP and 20TQ. This figure is highly debated as different manufacturers use different dynos with different cars with different levels of mods. It also varies because some headers incorporate an uppipe into their design. This makes it nearly impossible to compare the gains of a header without an uppipe vs. a header with an uppipe.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent “bad” headers on the market. Obviously, there may have been bad pipes sold, but not enough to report as “bad” overall.

Where can I find headers?

Subaru WRX STI Header Prosport Unequal Length Stainless Steel Header

Perrin Subaru STi /WRX Header Equal Length Big Tube

AP WRX/ STI Stainless Steel Unequal Length Header w/o Uppipe

Invidia HS05SW1HDR Racing Header for Subaru WRX STI/Legacy GT

Agency Power (AP-GDA-175) Unequal Length Header, Stainless Steel

Perrin PSP-EXT-050 04-08 STi /LGT/FXT/06-08 WRX (06+ WRX requires modification to oil cooler) Header (02-05 WRX Requires STi Oil Pan)

TOMEI 193082 Headers

What differences are there with headers? The main difference is exhaust piping length. Headers are made to be unequal length or equal length. Unequal means the piping on the driver’s side of the engine will be longer than the passenger’s side. Equal means the piping length is equidistant from the engine outlet to the header outlet for all piping.

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Intake pipe turbo subaru FAQ

Intake Turbo Subaru

The primary purpose of an aftermarket intake is to increase the amount of air flow the engine receives.

HP gain is 0-15HP. These HP figures are a range as different intakes have different dyno results.

What is an aftermarket intake? Aftermarket intakes can be broken down into two types:
1. Short ram: AKA shorty or ram pod.
2. Cold air intake: AKA CAI.

What does the stock intake look like? To gain a perspective on how aftermarket intakes function, the stock intake features will be shown and discussed for further clarity.

This is the stock intake as viewed from the driver’s side.
The “U” shaped assembly and the tank that connects to it on the left is commonly referred to as the snorkel,  silencer, or resonator. It is actually hidden in the fender.

Stock Subaru turbo intake piping.
Stock Subaru turbo intake piping.

This is the stock intake as viewed from the passenger’s side.

This is the stock intake as viewed from the passenger's side.
This is the stock intake as viewed from the passenger’s side.

This is the stock intake as viewed from above.
1. Stock “ram intake” funnel.
2. Stock air filter box.
3. MAF sensor.
4. MAF sensor piping.

This is the stock intake as viewed from above. 1. Stock "ram intake" funnel. 2. Stock air filter box. 3. MAF sensor. 4. MAF sensor piping.
This is the stock intake as viewed from above.
1. Stock “ram intake” funnel.
2. Stock air filter box.
3. MAF sensor.
4. MAF sensor piping.
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Intercooler Hose FAQ for Subaru STi/WRX

The primary purpose of an aftermarket intercooler hose is to replace the stock intercooler hose with a better flowing unit. Airflow testing indicates 14.2% better flowing capacity than the OEM piece. It can also decrease intake temperatures, increase reliability, and dress up the engine compartment.

HP gain is 5HP. This figure is highly debated as different manufacturers use different dynos with different cars with different levels of mods.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent “bad” intercooler hoses on the market. Obviously, there may have been bad hoses sold, but not enough to report as “bad” overall. The current manufacturers of intercooler hoses that fit the OEM intercooler are:

a. APS: “Y” hose only
b. Perrin: 3 hose set
c. Prodrive: “Y” hose only
d. Samco: 3 hose set
e. Vishnu: 3 hose set
f. GP Moto: 3 hose set

Prodrice silicone intercooler hose
Prodrice silicone intercooler hose

What intercooler hose material is best? Intercooler hoses are made from silicone and cast alloy. There is no irrefutable evidence that one material is better than the other. Obviously, heat soak levels are higher with the cast alloy model.

Which intercooler hose construction method is best?
There is no irrefutable evidence that one design is better than the other. With regard to the number of silicone plys, here is a breakdown:

Perrin= 5 ply
Prodrive= unknown ply
Samco= 3 ply
Vishnu= 3 ply
GP Moto= unknown ply

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TMIC basics on a Subaru WRX/STi

TMIC basics on a Subaru WRX/STi:

The primary purpose of a top mount intercooler is to reduce post turbo air temperature prior to entering the combustion chamber via the throttle body.

HP gain is around 15HP. This figure can vary as many TMICs replace the restrictive OEM piping and results can be further enhanced with post installation tuning. This is one modification that is extremely difficult to put a traditional HP figure on as results truly vary from car to car based on tuning and turbo output in terms of CFM.

How much HP can my stock TMIC hold? 300WHP on the WRX and 400WHP on the STi are attainable. That does not mean those power levels are 100% efficient, but that those power levels are attainable with their OEM TMICs. As discussed below though, TMICs are not meant to be HP rated, but rather CFM related, but this is an FAQ so the HP figures are given as a good “bad” answer.

TMIC basics on a Subaru WRX/STi: 04-07 STi oem TMIC
TMIC basics on a Subaru WRX/STi: 04-07 STi OEM TMIC

Which manufacturer is best? This topic is highly debated. There have been no reported consistent “bad” TMICs on the market. Obviously, there may have been bad TMICs sold, but not enough to report as “bad” overall.

I have a 2008/2009 model, any differences? Yes. Your engine bay has an entirely new layout vs. the 2002-2007 models.

TMIC basics on a Subaru WRX/STi: A 2008 STi stock TMIC
TMIC basics on a Subaru WRX/STi: A 2008 STi stock TMIC
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