Category Archives: Turbo

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.

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.

Engine Management For Subaru WRX/STi

 

Why do I need engine management?

 


Consider your stock engine management for just a moment. Your stock engine control unit (ECU) is a very complex piece of circuitry that calculates hundreds of variables every second. All of these variables rely on inputs within a + or – range. When you modify your vehicle, these values change. As long as the changes are within the values the ECU expects to receive, your engine runs fine. Once the values are exceeded, the ECU is programmed to compensate to return the values to normal levels.

A typical way of engine management is to use a Cobb Accessport.

This is a layman’s explanation of how your stock ECU can actually work against you when modifying your vehicle. This also explains why modifications can feel great once they are bolted on but the butt dyno results seem to fade over time. This is due to ECU compensation.

What is the first step in finding what engine management I need? Finding a tuner. The Tuner FAQ will help with the general rules of finding a good tuner. Remember, it’s always better to have a custom tune vs. a plug and play or “staged” map. Always defer to the tuner’s advice as to what to choose as ultimately he will be the one to provide custom support. Discuss your goals and budget and your tuner should set you on the right path. If you are a “plug and play” kind of person, review the options below and decide for yourself along with input from locals in your regional forum and the car parts review forum.

What will engine management do for me? Generally speaking, engine management optimizes several engine functions to create more horsepower and efficiency. The stock ECU is designed to ensure your car runs fine and monitors the engine’s output parameters. Utilizing an aftermarket engine management solution takes this to the next level.

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.

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.

McRae UK WRX 1st Gen special editions

McRae UK WRX 1st Gen special editions

Series McRae

In June 1995, to celebrate their winning of both the manufacturers and drivers World Rally Championship titles, Subaru in the UK released a limited edition run of two hundred cars (numbered 1 to 201 – no number 13!) prepared by Prodrive going by the name of the Series McRae. The main improvements over the standard model are:

  • Special mica blue paintwork
  • 6.5 x 16 inch eight spoke gold Speedline Safari alloy wheels
  • Pirelli P Zero 205/50 ZR 16 low profile tyres
  • Recaro sports front seats with open headrests and Series McRae motifs
  • All seats (front and back) and door panelling retrimmed in Le Mans/Avus material
  • Factory fitted electric tilt and slide sunroof
  • Interior numbered Series McRae plaque
  • Side and rear Series McRae decals

On the road price was £22,999

A official Subaru WRX poster for the Series McRae.

Next page will be the Catalunya edition!

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.

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.

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.

Downpipe Turbo Subaru FAQ

Downpipe Turbo Subaru FAQ

Buying a aftermarket downpipe is a typical modification which removes or replaces the stock catalytic converter with a better flowing unit. It also increases the exhaust diameter for better flow.

HP gain is 15-20HP. This figure is highly debated as different manufacturers use different dynos with different cars with different levels of mods. It also varies because some downpipes use one high flow cat, while others are catless and actually extend far enough back to eliminate the 3rd cat as well.

I have an 06/07 WRX, is the downpipe the same? No. The 06/07 WRX has a unique exhaust in that it’s downpipe is both the downpipe and catpipe sections of the “older” exhaust. This means you must use a “long” downpipe to bolt up to the rest of your exhaust system. A full TBE will fit fine, but when replacing just the downpipe, you must use a long downpipe.

I have an 08/09 WRX, is the downpipe the same? No. The 08/09 WRX has a unique exhaust in that it’s downpipe is the same, fitment wise, as the Legacy GT. So if you have one of these models, you must ensure you state your model/year to your vendor or specifically request the “Legacy GT downpipe” for your car in order to assure proper fitment.

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

What downpipe metal material is best? Downpipes are made from mild steel and stainless steel (304 & 321). There is no irrefutable evidence that one material is better than the other. Obviously, corrosion levels are higher with mild steel (coated or otherwise). Article on exhaust materials.

Which downpipe construction method is best? Downpipes have 4 main construction methods:
1. Blank plate: Identical to stock construction with the wastegate portion completely covered.
2. Bellmouth: Completely open design.
3. Split bellmouth: Similar to bellmouth only with a divider inserted to separate the wastegate.
4. Divorced or Twin Dump: Separate exhaust and wastegate piping that connect further downstream.

There is no irrefutable evidence that one design is better than the other. The thought process is that the greater the separation there is between the wastegate gases and exhaust gases, the smoother the overall exhaust flow.

BOV: Blow off Valve Subaru FAQ

BOV: Blow off Valve Subaru FAQ

Term usage: “Blow off valves” go by several names, among them are compressor bypass valve (CBV), air by-pass valve, bypass valve (BPV), blow off valve (BOV), Diverter valve, and possibly a few others. BOV is the common and incorrect term that lumps true blow off valves and bypass valves under the same term. For the sake of correctness, this post will refer to either aftermarket BOV, aftermarket BPV or OEM BPV as these are the most correct terms.

What is the function of a blow off valve (BOV)? To release pressure from the intake tract of a turbo car when the throttle closes. It is a vacuum-actuated valve designed to releases the air to the atmosphere.

What is the function of a bypass valve (BPV)? To release pressure from the intake tract of a turbo car when the throttle closes. It is a vacuum-actuated valve designed to recirculate the air back into the intake before the turbo inlet, but after the airflow sensor.

A stock Subaru BPV (not a BOV).

What is the purpose of a BOV/BPV? When the throttle closes and the intake system is under pressure, the high-pressure air entering the motor will bump into the closed throttle plate, and in the absence of a BOV/BPV, a pressure wave will travel back to the turbocharger. The result is that the compressor wheel will stall (a phenomenon known as “compressor surge”) and slow down very quickly. This is hard on the bearings and decreases the turbo’s lifespan, but it also means the turbo will take longer to spin up the next time the throttle is opened.

Are aftermarket BOVs necessary with Subaru turbos? No. The OEM BPV is perfectly fine up to 20psi of boost. For applications using higher boost levels, an aftermarket BOV/BPV should be considered.

Can I mod my stock BPV to hold higher boost? Yes. I’ll be creating a post giving detailed instructions on how to do so.

Is the STi BPV better than the WRX BPV? No. They are the same. However, the JDM STi BPV will hold more boost as it is physically different than both the USDM STi BPV and the WRX BPV. The specific PSI rating of the JDM STi BPV is unknown, but users have reported it is good up to 25 PSI.

Is an aftermarket BPV better than the stock BPV? No. Unless you are considering an aftermarket BPV solely for the purposes of holding higher boost levels. An aftermarket unit should sound just like the OEM unit.