The Standard Turbocharger...
The MY94 WRX started life with a relatively large Mitsubishi TD05 turbocharger - a unit that does taWke a while to come onto boost, but gives tuners the potential for impressive top-end power. Post October '96 models (MY97s) sported a significantly smaller TD04 turbocharger - much quicker to boost, but inevitably lacking in its high rpm puff. Notice that the big turbo'd '94 WRX produces maximum torque (270Nm) at 4800 rpm, while the slightly harder-boosting MY97s make 290Nm at a much lower 4000 - that tells the turbo sizing story all on its own... A very much different type of turbocharger is used in Australian-delivered STis. These vehicles spin a roller-bearing IHI RHF5 turbocharger that helps to deliver an impressive 353Nm or torque.
All WRX models mount their turbocharger off a short top section of exhaust manifolding using the same 3-bolt flange (plus they carry over same dump pipe pattern as well). An internal wastegate is also set deep into the turbine housing. Structurally, the major change occurred in the MY97 update - this saw the '94's cast elbow (leading into the mouth of the compressor) abandoned for a straight inlet.
An easy place to start is to convert your late-model TD04-equipped WRX to run with the earlier TD05. Notice that the Mitsubishi-built TD05 has a larger compressor and a larger turbine side - the same sleeve-type bearing is carried over. The (2-wheel) dyno graph shows the significant difference that there is between the two genuine Subaru turbochargers - as tested on a MY99 fitted with a 3-inch exhaust. The larger TD05 turbo does lose torque at lower rpm but picks up at over about 2000 rpm. At about 6000 rpm, engine power is up by 10 per cent - though, unfortunately, peak power was unable to be measured on this 2WD chassis dyno configuration. As stated by the installer of the TD05 turbocharger, "it doesn't go to 5000rpm and then just stop like it did before. The top-end power gains more than make up for the bottom-end loss - and when you're going hard, you're never down there anyway". How true!
Converting a post-MY97 vehicle to the earlier turbocharger is a very near bolt-on operation. It does, however, require that the compressor housing have its cast-in elbow removed and replaced with a machined pressed-in aluminium sleeve. The only other change is the modification of the turbocharger water fittings.
Mitsubishi TD05 turbos can be bought directly through your local Subaru dealership.
Power Turbo(formerly Pro Spool Technologies) is the largest Australian source of WRX-compatible turbochargers. They are a primary retailer of Garrett, Turbonetics and IHI products.
Certainly, one sure-fire way of achieving a good balance between top-end power and street-useable low-down torque is to copy the IHI turbocharger that Subaru used in its own 206kW STi WRX. However, aftermarket tuners can chose from any of the IHI VF turbos - the VF22, 23 and 29 being the most common and readily available. Note that all VF-series turbochargers use the same roller-bearing, water-cooled core assembly - just different wheels and housings to achieve different flows. The VF22 gives the scope for the most peak power, the '23 is the middle ground and the VF29 delivers a slight (but very wide) increase in torque over the standard TD-series turbos. All IHI VFs are direct bolt-ons.
Power Turbo is situated in Brisbane.
Melbourne's Advanced Vehicle Operations (AVO) offer several sizes of bolt-on turbocharger upgrades. These, too, have a roller bearing centre to aid in fast transient spool-up time - but also 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. All are ultra-strong and AVO has run their 400hp beastie to well over 28 psi boost... Note that these turbos are available to suit all model WRXs, as you can buy them with or without the cast elbow leading into the compressor.
AVO is a Melbourne workshop.
BR Developments in the UK - after extensive development with Turbo Dynamics Ltd - can now supply you with up-rated versions of VF-series IHI turbochargers - the whole range of '22s, 23s, 24s, 28s and 29s. These turbos feature "proprietary design alterations to the compressor, exhaust turbine and/or wastegate valve". While a number of established design/modification options already existed, the BRD/Turbo Dynamics development was intended to deliver "improved low-to-mid rpm performance, quicker spooling up characteristics as well as strong results above 4000 rpm combined with solid and stable boost control". These can be bought new, as exchange or as revised owner's units.
BR Developments is in the United Kingdom.
Many sub 13 second WRXs are running an
A'PEXi turbocharger. Certainly - as part of a typical exhaust, intake, intercooler and boost package - they make an excellent bolt-on shove-in-the-back. A'PEXi AX turbos are the product of a joint venture with IHI turbos and - as such - are very similar to the VF-series turbos. The A'PEXi version, however, comes with an adjustable internal wastegate and an industry first "abradeable seal".
This unique seal surrounds the compressor blade and serves to create minimum (otherwise wasted) clearance. The turbocharger to seal clearance is set by the compressor actually grinding away the seal to give just enough clearance. Of course, the A'PEXi AX turbo is also a roller bearing turbo design - "to provide fast response and maximum power through out the rpm range".
A large step up from this is the AX5 turbocharger. Reputed good for an easy 450hp, this turbo is also developed in conjunction with IHI and is essentially just a larger body version of the AX. Featuring a lightweight turbine wheel and a roller bearing centre, this turbo - like the AX - will also fit all MY WRXs.
A'PEXi turbos are available through BEL Performance, BGT, BEL Performance and Jap Trading.
Japanese go-fast manufacturer Trust/
GReddy offer their "upgrade turbine kit" to suit both pre and post MY97 WRXs. Using a TD06 20G turbocharger, this bolt-on conversion - as far as we can determine - doesn't use a roller-bearing centre, but it is extremely durable. Its optimised turbocharged aerodynamics are also said to deliver a marked improvement in power and response.
GReddy turbos can be purchased through Evolution R.
Maximum Power Turbos - Where More Power Just Isn't Enough...
While this turbocharger is definitely not a bolt-on replacement onto the factory exhaust manifold flange, similar monster-turbo conversions can be achieved with relatively little fuss. Because the standard exhaust manifold has a separate upper half, it is quite simple to fabricate a replacement section that will allow the location of a totally different turbocharger. Custom oil and water fittings and a new dump pipe may also be required.
On the above 10-second Rigoli WRX - for example - that's just what they've done to locate a dirty big T60/T70 Turbonetics roller bearing turbo (teamed with a Turbonetics 42mm Racegate).
Here's a few other extra high hp turbos you might consider if you're chasing bulk performance...
Ray Hall Turbochargers offer a wide range of Garrett Phase II turbochargers for universal fitment. Interestingly, Ray strongly recommends steering clear of the older style turbos such as the T04B and E and T-series hybrids. Instead, he says that the new Garrett GT-series roller bearing turbocharger is - without a doubt - the way to go. Not only does the GT-series use a "full cartridge" dual bearing system (qualified in various OEM production based programs), it also incorporates the best in aerodynamic design - something people often overlook with the latest roller bearing turbos. And, as always, the new bearing core also has vastly improved strength over a sleeve type, and is inherently more tolerant to backfires and other high stresses.
The smaller GT25 roller-bearing range spans from a rated 280hp (max 335hp) to 440hp (500hp max) - good turbos for the serious streetcar/racer. Moving up a category, the bigger GT30 turbos extend from a listed 600 to 700 horsepower. All are supplied with an internal wastegate.
Ray Hall Turbocharging is in Cairns, Queensland. Garrett 'chargers can also be bought through Power Turbo.
In the Turbonetics range - available through Power Turbo - the ultimate offering is the T-series roller-bearing turbo. These use a roller bearing on the compressor side of the turbo only. Produced in a wide range of flow capabilities (TSO4, T61, T64, T66, T70, T72 and T76) compressor maps for these devices are also on-view at the Turbonetics website (http://www.turboneticsinc.com). These turbos give serious flow for a maximum power output of up to 1200hp (!). Options include dry or water jacket bearings, a range of turbine housings and polished compressor housings on some models.
Note that all Turbonetics turbos are built specific to your requirements - there are none available simply "off the shelf".
Contacts:
Evolution R (VIC)
+61 3 9543 6255
www.evo-r.com
Power Turbo (QLD)
+61 7 3876 8366
www.powerturbo.com.au
BGT (VIC)
+61 3 9874 8866
www.bgtperformance.com.au
AVO (VIC)
+61 3 9584 4499
http://www.avoturbo.com/
Jap Trading (VIC)
+61 3 9873 0133
www.jap-trading.com.au
BEL Performance (NSW)
0412 262888
www.belperformance.com.au
BR Developments (UK)
www.brdevelopments.com
Ray Hall Turbocharging (QLD)
+61 7 4051 6672
http://turbofast.com.au
If you listen to some people, you could be forgiven for assuming that the OE manufacturer always fits stupidly small turbos - just strangling power. In fact, new car manufacturers are primarily concerned with getting good turbo responsiveness relatively low down in the rev range and at throttle positions of less than Wide Open! The result is that the turbine side of the turbo (the bit that the exhaust gases flow through) is made small enough that it can whiz up to speed relatively easily. This gives low-down boost... however, when the gasflows in and out of the engine are raised (eg by fitting an intercooler, exhaust and winding up the boost), then that small turbine can also pose a major restriction to exhaust gasflow out of the engine. So, a bigger turbo can improve power, not only lowering exhaust flow restriction out of the engine but also pressurising enough air to maintain higher boost pressures right through the rev range. However, that bigger turbo will also be slower to boost on throttle transients (eg going from a light throttle cruise to full throttle) and will not develop full boost until higher engine revs are achieved. In fact, it's not at all hard to fit a turbo to a WRX that's so big that full boost isn't developed until 5000 rpm - even at full throttle.... By far the best way of selecting a new turbo that will both reflect your need for power and still satisfy your driveability criteria is to drive a car equipped with the new turbo that you're thinking of buying. Make sure that the car also has other mods similar to your car (eg a front-mount intercooler with larger diameter plumbing will affect the way in which the turbo comes on boost) and is running a boost level similar to that which you'll be using. And when you drive the car, don't just fang it through the gears - even big turbo cars feel good driven like this. Instead, select a high gear (eg 4th) at 60 or 70 km/h and floor the throttle. Does the turbo come on boost - instantly? After a few seconds? Never? Drive at part throttle through the gears - like you do every day in city traffic. Is there any boost? Does the car feel gutless and unresponsive, or is there get-out-of-trouble power just an ankle movement away? Be especially wary about workshops that just tell you what the peak power will be raised to when you buy that big turbo. How often are you at peak power? In a road car - even one driven hard - very, very infrequently. Fitting a big turbo is a bit like selecting a hot cam in a NA engine - it's easy to lose mid-range and bottom-end grunt while realising power right near the redline. But at least with a big turbo the idle will still be nice... Julian Edgar
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