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Subaru Impreza WRX STi AVO - Of Powerful Dreams

Avo Turboworld Sti

Adam S. Geczi
Nov 1, 2007 SHARE
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Few things in the material world are as exhilarating as a purpose-built race car. While many dream about building one, most find modifying a street car far more affordable - and practical for that matter - seeing as how most lack the big corporate backers to offset the cost. Perhaps all is better off this way, but if daydreaming is a definite prerogative, here is something from AVO Turboworld that will decidedly instill the ring of a lullaby in your ear, maybe even a love song.

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The righthand drive, 600hp AVO Subaru Impreza WRX STi demo car is crammed with the most extensive list of features to meet the challenges of even the most demanding race circuits and still leaves room for sporting a striking exterior. Without admitting to the popularly demonized shallow nature of physical attraction, the noticeably wider body of the AVO STi is far more attractive than its factory built counterpart. Not that there is anything wrong with a narrow rear end, but in terms of packing tires and gripping the road, the added width is undoubtedly preferable. In this case, the wider body allows for the fitment of a set of 265/35R18 Dunlop Direzza Z1 tires mounted on custom built +18mm offset 10-inch wide Rays Gram Lights. By comparison, Subaru installed 225/45WR17 Bridgestone Potenzas on '05 WRX STi models sold in the United States.

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The chassis of the widebody AVO STi is a combination of lightweight carbon-fiber composite and sheet metal. The car began life as an Impreza WRX STi Spec C Type-RA, available only in the Japanese domestic market, but the lightweight, no-thrills, rally-going production body has been significantly transformed. The hood panel is a lighter and stiffer carbon-fiber replacement of the factory aluminum. The wider front panels are bolt-on custom-formed steel fenders, while the wider rears are cutout replacement custom-formed, welded and blended overfenders. Custom carbon-fiber bumpers are matched to the wider front and rear body panels. Fiberglass side skirts from a custom mold complete the distinguished look.

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At the heart of the AVO STi is a new 2.5L, Cosworth-built, Subaru EJ257 high-performance long-block assembly. The EJ257 incorporates a semi-closed deck, a Subaru modification that facilitates boost pressure in excess of 10 psi. The advantage is that semi-closed deck engine blocks are less susceptible to cylinder wall flex thereby reducing the probability of premature head gasket failure. The CS600 is precision built with Cosworth and STi components. Forged pistons and forged H-beam connecting rods are mated to a STi crankshaft, which ride on high-performance trimetal rod and main bearings. The five-axis CNC ported cylinder heads with 1mm oversized intake and exhaust valves improve intake airflow by 22 percent and exhaust gas flow by 44 percent, when compared to the stock STi cylinder head. The heads are bolted to the block with 11mm steel studs and sealed with multi-layer steel head gaskets. The AVCS STi heads are also fitted with a number of other upgrades; high-performance valve springs and titanium retainers permit a 10,500rpm redline. The 10.9mm intake and 10.28mm exhaust high-lift camshafts support 278 camshaft degrees of intake and 274 camshaft degrees of exhaust duration respectively. This $12,000 upgrade, available through AVO Turboworld and other Cosworth distributors, is assembled with the utmost care using the finest Cosworth components to make it synonymous with perfection and reliability.

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A full line of AVO high-performance products developed and displayed in the demo car complement the longblock perfectly. However, nothing expands the capabilities of the engine as profoundly as the AVO550 ball-bearing turbocharger, which is based off the Garrett GT series rotating assembly. The turbine housing and compressor cover are proprietary to AVO, but cooling and shaft support is the highly reliable Garrett technology. The turbocharger assembly is mounted to a prototype equal-length stainless steel exhaust manifold and 3-inch diameter downpipe. The product is 26.1 psi of boost at 4,100 rpm when complemented with an air intake system that is comprised of a carbon-fiber cold air box and 80mm Kevlar-reinforced silicone intake pipe, as well as the AVO Power Air Intake system for charged air delivery. The latter also includes a bar and plate style front-mount intercooler.

Although AVO has developed other noteworthy engine components for this wide-body track-bound demo car, they also sourced some of the best high-performance drivetrain, suspension and brake components in the business. The Exedy carbon clutch kit for the STi is one such technologically advanced component. The carbon-steel multi-plate clutch is a lightweight upgrade from the conventional metallic clutch, which does not have the heat-dissipating characteristics that carbon materials possess after being baked at 3,600 degrees F. The outcome is reduced clutch slippage and quicker, more consistent engine-to-transmission coupling.

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In an effort to fully exhaust the issue over friction and traction, AVO modified the STi clutch pack Type-R180 rear limited-slip differential to increase the breakaway setting from the factory adjusted 45 lb-ft with the use of shims. This alteration is normally very delicate since the only way to find out the results is to reassemble the entire differential. A relatively minor change in shim thickness can increase the breakaway setting beyond 150 lb-ft, a situation that would cause the differential to behave more like a locked one than one designed to slip. This would probably be acceptable in a rally car that spends ample time traveling sideways, but would give a track car a serious case of understeer and probably cause overheating in the differential. Of course, done right, the higher breakaway setting would increase grip by maximizing the time that torque is delivered to both rear wheels, before allowing the two output shafts to spin at different speeds.

Speaking of friction, Disc Brakes Australia is a household name for demanding applications and as such supplied the two-piece 5000 series enhanced-performance slotted front rotors and the 4000 series solid slotted rears. The obvious advantage of this setup is improved heat dissipation and reduced stopping distance but the thermographic paint markings that aid in heat monitoring are also notable features. These rotors are fully compatible with the STi brake system, which is comprised of Brembo four-piston fixed calipers in the front and two-piston fixed calipers in the rear.

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Since no race car preparation is complete without attention to handling and the mechanical grip offered by a properly tuned suspension, AVO partnered with Original Box, a racing suspension specialty company based in Atsugi, Japan. The result is an uncompromising suspension, one with a fully adjustable coilover system featuring custom shock valving designed specifically for time attacks. AVO adjustable 21mm solid front and 22mm rear stabilizer bars with polyurethane bushings keep the suspension tight.

With a body made for seduction, a heart to excite and a soul to burn, the performance engineered AVO Subaru Impreza WRX STi is within reach even though it seems like a dream.

Avo Subaru Impreza Wrx
Engine
Cosworth CS600 blueprinted and balanced
2449cc short block
Cosworth 99.5mm Forged Pistons
Cosworth Forged H-beam Connecting rods
STI Forged Crankshaft
Cosworth STI CNC Ported Big Valve
Cylinder Heads
+1mm larger intake valves and +1mm larger exhaust valves
High-performance valve springs
Titanium Retainers
Cosworth high-lift camshafts
Cosworth High Performance Cylinder Head Stud Kit
Cosworth High Performance Trimetal Engine Bearings
AVO550 Ball-bearing Turbocharger
Garrett GT Ball-bearing CHRA with AV04-5 Exhaust Housing and AVO Compressor AVO 80mm high-flow Silicone Intake Pipe.
AVO Power Air Intake system.
AVO Carbon-fiber Cold Air Box
AVO 800cc hi-flow Fuel Injectors
AV0 255 lph hi-flow Fuel Pump & Bosch 600hp
Fuel pump combination
AVO fuel surge tank
AVO Oil Catch Tank
AVO Blow-off Valve
AVO Front Mount Intercooler Kit
Kevlar reinforced 3" rubber hoses, stainless steel pipes and cast aluminum pipes.
WRX LinkG3 standalone engine management.
Knock Link engine detonation detection system
STACK ST8820S/S2 Configurable Dash Logger
System and Display Unit
Innovate A/F Meter Unit
Two separate DCCD Center Differential controllers
AVO prototype Equal Length StainlessSteel 4-1 Exhaust Manifold
AVO Downpipe with cast-iron exhaust bellhousing and 3" mandrel-bent stainless piping.
AVO 3" mandrel-bent stainless steel cat-back exhaust system

Drivetrain
Subaru 6-speed DCCD manual transmission
Exedy carbon-fiber clutch
AVO Polyurethane transmission bushing set
STI rear LSD with STI upgrade shim kit

Suspension
Suspension Drive coilover suspension system.
AVO adjustable 21mm solid front stabilizer bar
AVO adjustable 22mm solid rear stabilizer
AVO pillow-ball adjustable stabilizer bar end-links

Brakes
DBA 5000 series 324mm slotted front brake rotors.
DBA 4000 series 316mm slotted rear brake rotors.
STI Brembo 4-pot front brake calipers
STI Brembo 2-pot rear brake calipers

Exterior
STI RA with lightweight glass
Carbon fiber hood
Custom widebody steel front fenders
Custom steel rear overfenders
Carbon fiber front bumper
Carbon-fiber rear bumper
Fiberglass side skirts
Spot-welded body seams

Interior
Works Bell steering wheel boss
Momo MOD 07 Suede Steering Wheel
Recaro RS-G FIA approved Racing Seat
Schroth Racing 5-point racing harnessCusco Racing Cage

Wheels/Tires
Gram Lights Pro 10JJ x 18" with +18 offset. 5x100 PCD
Dunlop Direzza Z1 265/35 R18

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By Adam S. Geczi
17 Articles

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