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Tech-Talk 01

Step-By-Step Guide: Turbo swap

The UK’s leading Impreza specialist, Derbyshire’s Scooby Clinic, shows us what’s involved when you decide to upgrade your blower

WORDS & IMAGES: Matt Robinson

The Type R used for our step-by- step guide was a tasty looking competition car, whose owner is now looking to achieve a 10s quarter on the SC36 kit.

OK, slight confession to make – the car having the turbo swap today is a GC8 Type R Coupe, which already has a Scooby Clinic SC46 turbo on it… and it’s having a smaller SC36 fitted. Why, you may ask? Well, its owner is keen to set a 10s quarter-mile on the SC36, which would be a national record – and the SC36 should offer more low-down torque and responsiveness, if slightly less top-end power, than the SC46. Although this car is well known to Scooby Clinic, Mark power runs it on the Dyno Dynamics rolling road to check what its current power figure is, just to ensure the car is in fine health (and not missing any bhp it should be packing). It records 295wbhp (c.410bhp at the flywheel), which is about right for the car in its current spec.

This shows the SC36 is a genuine twin-scroll turbo – these are the twin volutes.


This is the magic of the SC turbos; the CNC-machined, billet compressor wheel. ‘Tis truly a thing of beauty…


verybody knows that the turbo is one of the things that makes the Subaru Impreza great. From the first GC8s with

204bhp to the Cosworth STI CS400, it’s the forced induction for the boxer engine which entertains enthusiasts and ensures the marque’s avid following.

And, as sure as night follows day,

everyone also knows that those same enthusiasts will – once they have a treasured Scooby in their possession – want to upgrade said turbo for something bigger, better and giving even more power. The UK’s largest Subaru specialist is Scooby Clinic, perched on the edge of the Peak District and now in its 25th year of modifying all things Subaru. Handily, one of the company’s signature

upgrades is fast-spooling twin-scroll billet turbos, available in convenient bolt- on format for EJ20s, EJ22s and EJ25s – and all variations thereon (2.33-litre strokers, for example). These turbos benefit from the

very cutting edge of precision CNC machining; the key aspect being the compressor wheel of the turbine itself, which is much stronger than a standard compressor, 30 per cent lighter and it delivers the twin holy grails of turbo upgrades – namely, faster spool-up and more top-end power.

No wonder these things are in big demand. Scooby Clinic does a range of bolt-on billet turbos, from the SC36 up to the SC54, the two figures at the end roughly denoting the power output you would expect once the turbos are fitted and the car is mapped properly (360-

540bhp). “We are two years ahead of any other company in the UK when it comes to these billet turbos,” says Scooby Clinic’s MD, Kevin Knight. “People are trying to copy us but they are not matching our products for spool-up and power delivery.

“Our SC kits are true twin-scroll turbos – the turbines have twin volutes, twin snails and twin wastegates. Some other companies claim their turbos are twin- scroll but in actual fact they’re only twin entry.”

So, getting rid of your IHI blower for a Scooby Clinic SC package seems to be a good bet. We joined technician Mark Pettitt in the workshop to see what’s involved in swapping your old blower for the very cutting edge of turbine technology…

With the bonnet up, Mark sets to work. The first thing to remove is the top-mounted intercooler. Two 12mm bolts hold this down either side of the intercooler, and once they’re removed you can disconnect the hoses too.


Mark undoes the dump valve by undoing a further two 12mm bolts, then sets to work undoing the two jubilee clips on the throttle body and one on the turbo itself.


Mark decides to remove the strut brace. This isn’t strictly necessary but unless you want it scratched to buggery when removing the intercooler, it’s probably for the best. The brace is held in place by more 12mm bolts (pictured) on the top mounts of the suspension.

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With all bolts and hoses undone, you can now remove the strut brace and the intercooler.

Next, remove the 12mm bolt holding the intercooler bracket in place and then take out the bracket itself.

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