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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Wednesday, February 02, 2011 2:23 AM
Nice article. I believe FP compressor wheels are proprietary though.
yo vanilla
yo vanillalink
Wednesday, February 02, 2011 3:40 AM
she's a beaut!
Wednesday, February 02, 2011 5:31 AM
Always wanted a sneak peak under the skirt of this hootie, now we know "all" of your secrets, muhahaha....

Whiteline roll center and bumpsteer correction kit on the front end not found?
Wednesday, February 02, 2011 8:02 AM
looks like a 6gun kit to me. You also say drysump but I see a stock oil pan in all those pics. I don't get the twinsroll turbo on a single scroll up-pipe though.

Liking the o-rings and oversize headstuds
Scott Helmer
Scott Helmerlink
Wednesday, February 02, 2011 8:29 AM
Good Golly miss Molly! I'm so glad you guys did an article on this sexy beast, it's easily one of my favorite, if not my most favorite, Time Attack cars (especially since my personal ride is a '99 Impreza 2.5RS). I'd love to do my Impreza up in a Time Attack theme (and actually to some extent I intend to), but I'm not really a big fan of the GT-style fenders with the big freakin' holes on the backsides of said fenders. A well-designed widebody, a decent wing, and some underbody aero are really all I could see myself wanting/doing, which is why I'm thinking of going the route of '99 WRC fenders from subaruwrcspares, assuming they don't break the bank for me. Gotta get my hands on a good v7 or newer engine/drivetrain swap and some suspension/brakes before I get too far ahead of myself, though. I'm about to attempt advancing my ignition a few degrees for a few more horsepower, but the SOHC EJ253 I've got hasn't that much power in the first place :/. I sure as hell ain't gonna waste my time (or more importantly, money) turbocharging it.
Wednesday, February 02, 2011 8:37 AM
Scott, call up aerosim research in costa mesa, they make a great widebody kit for the GC at a much lower cost than the real WRC parts.
Mike Kojima
Mike Kojimalink
Wednesday, February 02, 2011 11:04 AM
A lot of those pictures are older from the first RTA at Cal Speedway so some stuff has changed in the time since the pics were taken and the story written.
Wednesday, February 02, 2011 11:13 AM
Mike K is correct a lot of these pictures are from some time ago, in fact if you were to take pictures of the car currently it would again look vastly different.

JC - Trust me there are still a few things up this girls skirt that nobody knows about especially since the off season rework she's nowhere near the car she was last year :)
Mike Kojima
Mike Kojimalink
Wednesday, February 02, 2011 11:17 AM
We want to revist the updates on both of your cars soon. We took the pic of the GST car during an all out thrash to get the car back on the track, hence the pictures which are not up to our usual quality.

I was hoping to get a different look but it didnt work out like I though it would.
Dusty Duster
Dusty Dusterlink
Wednesday, February 02, 2011 11:38 AM
Awesome article. I could stare at pictures of well-built race cars all day.
Eric Hsu
Eric Hsulink
Wednesday, February 02, 2011 6:58 PM
I've always been a fan of this car. It sounds like it will be hauling even more ass in 2011. Mike (Warfield), don't disappoint us!
Sunday, April 24, 2011 6:10 PM
Pretty sure thats not Not a TS header then or now.
Mike Kojima
Mike Kojimalink
Sunday, April 24, 2011 6:19 PM
We wrote what Mike Warfiled told us it was.
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