Project GD STI – Improving the Fuel System with Injector Dynamics and Other Details


The Perrin intake fits, barely.  Look at the packed mess of stuff that is under a Subaru intake manifold.  It is one thing just to throw parts in there but to make sure nothing rubs, chafes or wears to cause shorts or leaks down the road takes some patience and careful thought.
Subarus are known to be oil burners when driven hard.  According to our friend, Subaru tuner extraordinaire Quirt Crawford, most of the engine oil burning issues are due to the engine’s poor handling of blowby.  The Subaru blows a lot of oil out of its breather and PVC system.  Crawford has developed an air oil separator to eliminate this problem.  The Crawford AOS replaces the stock  PCV and all crank case breathers are routed to a self draining can.
The heart of the Crawford AOS is the separator can.  Blowby gasses are swirled to centrifugally separate the oil out.  The gasses are then run into a secondary chamber where any oil that makes it past the first chamber is removed.  The oil free gas is vented out the top into the car’s intake and the oil returned to the crankcase.
The AOS took us awhile to install as we were really careful about the hose routing through the mess under the intake manifold.  The installation hassles are well worth it.  Not only will the AOS greatly reduce our oil consumption but it will also reduce detonation as oil in the intake charge reduces the fuel octane.  It will also eliminate the tendency for Subarus with front mount intercoolers to fill up the intercooler with oil!
While we had much of the engine bay disassembled, we also installed Perrin’s master cylinder stopper.  The master cylinder stopper bolts to existing bolt holes in the shock tower and braces the end of the master cylinder reducing firewall flex and giving a more solid feeling brake pedal.  You would not believe how much the firewall can flex when pushing on the brakes hard, most cars flex at least a 1/4″ and when multiplied by the brake pedal ratio this can introduce quite a bit of mush into the pedal.
On top you can see the relocated fuel pressure regulator, down below the Perrin master cylinder brace.  We were amazed how much of a difference the brace made in pedal feel.  With our super stiff Stoptech Trophy calipers, we have some of the best feeling brakes of any of our project car fleet.

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