No It’s Not an STI: GST Motorsports Mighty Subaru Impreza

No It's Not an STI: GST Motorsports Mighty Subaru Impreza

No It's Not an STI: GST Motorsports Mighty Subaru Impreza

By Mike Kojima

 

We have always been fans of the GST Motorsports 1996 GC8 Subaru Impreza L.  The car with driver Jeff Westphal is the current reigning Redline Time Attack Super Modified AWD Champion.  The GST car has been around forever and has been in a continuous state of development since 2006. 

The car was purchased in 2003 by GST owner Mike Warfield who intended it to be his daily driver where it served well until 2006 when Mike decided to build it into a race car for NASA's 25 hours of Thunderhill. After the race, it was decided to continue to build the car, making it into a dedicated time attack car and its journey to the all dominating AWD Unlimited class car we know today began.

 

No It's Not an STI: GST Motorsports Mighty Subaru Impreza
The thickwall Darton Sleeves are buttressed into the engine case.  This helps reduce flex and improves head seal.  The sleeves are o-ringed with copper for a better seal.  The JE FSR forged pistons are 9:1 compression.  ARP head studs are used.
No It's Not an STI: GST Motorsports Mighty Subaru Impreza
A Perrin underdrive front pulley reduces parasitic loss.  A Cosworth dry sump system is used although the drive is not visible here.

The heart of any Unlimited class car is the engine and the GST car delivers in gobs here.  It's hard to keep an EJ25 engine together under brutal high boost road racing conditions at power levels beyond the mid 500s.  The GST car easily does this and much beyond.  It helps when the engine is built with a sturdy array of parts.  Cosworth CNC ported, big valve cylinder heads help the engine breathe.  Cosworth valve springs and retainers keep valve motion under control at high revs when moved by BC 280 cams.

No It's Not an STI: GST Motorsports Mighty Subaru Impreza
We wanted Jeff to take tech pictures but he took pictures of what looks like random parts lying on the ground.  These are actually Cosworth big valve CNC ported cylinder heads and Cosworth MLS head gaskets.  You can also see a couple of the 4 BC 280 cams as well.  Sorry for not getting close enough for real details.

The block is fortified with buttressed Darton sleeves to keep the cylinders from walking at high boost levels.  To keep the block halves from walking, a high powered EJ25 problem, the parting surfaces are pinned.  This helps main bearing life and supports the crank better.  9:1 compression JE FSR lightweight forged strut type pistons are used supported with BC I-Beam connecting rods.  The rods are hung on a BC billet crankshaft.  The crank and rods spin on ACL coated bearings.  A Cosworth dry sump system keeps all the reciprocating parts well oiled under high G-loads and rpm. ARP fasteners are used to hold the bits together. Cosworth MLS gaskets seal the heads. WAR heavy duty motor mounts keep the engine in place.

No It's Not an STI: GST Motorsports Mighty Subaru Impreza
The Full Race divided header takes full advantage of the twin scroll Forced Performance HTA 3586 Turbo.

 

No It's Not an STI: GST Motorsports Mighty Subaru Impreza
The GST crew scrambles to fix a head sealing issue at Cal Speedway.
No It's Not an STI: GST Motorsports Mighty Subaru Impreza
The clutch is surprisingly conventional considering the car's power and AWD clutch abusing traction.  An ACT Extreme pressure plate, sprung hub six puck disc and ProLite flywheel harness the beast.

No It's Not an STI: GST Motorsports Mighty Subaru Impreza  

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