This engine we designed and prepared for a local Subaru tuner. Engine will be fitted to a 2008 Subaru Impreza STI using a Garrett GTX3076R ball bearing turbocharger, ID1000 injectors, and E85 fuel. Goal is reasonable street use response, thanks in part to a PRE-designed V-band turbine housing system, dual AVCS, and ECU calibration. Vehicle will also be use for road course racing locally in the Midwest. 450whp on “pump” fuel and 550whp on E85 are the goals which will soon be tested.
PARTS AND SERVICES
ENGINE BLOCK: Engine started out as an EJ22T closed deck block sourced half way across USA. Block was media blasted, cleaned thoroughly, deck milled, cylinders bored and honed as an assembly with two torque plates, and align honed. Block was mock-assembled numerous times checking bearing clearances and setting piston ring gaps. Each case half deck height was measured and milled different amount to be equal height.
CRANKSHAFT: Engine fitted with a brand new modified Subaru heat treated crankshaft. Crankshaft was machined to accept thrust at #3 position. Crankshaft was also performance balanced.
PISTONS: PRE-designed forged pistons are at the heart of this project. Strutted forging increased skirt and pin boss stiffness without weight penalty. Pistons designed in conjunction with Carrillo connecting rod pin end dimension. Narrow pin boss spacing reduces piston pin bending and actually work in double shear. Short piston pins reduce flex and weight. Piston pins made of tool steel and thick-wall design for heavy duty turbocharged application. Lateral gas ports for top compression ring utilize combustion gasses to aid sealing. Piston compression ratio depends on which cylinder heads used: this engine uses EJ257B W25 casting dual AVCS heads and final compression ratio is 8.4. If using single AVCS Ej255 D25 casting heads or EJ205 heads the compression ratio will be 9.0. Stay tuned for a another project using EJ22T stroker short block and D25 EJ255 heads. Piston compression height was designed for stock thickness head gaskets. We can design similar pistons for use with Cometic or Roger Clark Motorsports(RCM) head gaskets.
CONNECTING RODS: PRE uses Carrillo PRO-SA I-beam design forged connecting rods with WMC bolts. I-beam connecting rods were selected based on the low weight requirement while maintaining buckling stiffness. Connecting rod bearing ends and pin ends were measured and recorded. Connecting rods were weighed on the pin end, bearing end, and total weight. Connecting rods weight matched as a set to be within 0.5 grams. All our connecting rod bolts always tightened using a rod bolt stretch gauge. Torque wrench is not accurate enough and used for reference only.
BEARINGS: We use ACL Race series tri-metal connecting rod bearings and King XPG main bearings. King XPG main bearings offer superior profile and oil hole design.
CASE BOLTS: We use ARP case bolt kit for this engine. Block bearing housings were checked using stock and ARP bolts. The block was align honed using ARP bolts.
HEAD STUDS: We use a conventional ARP head stud kit for this engine. Block was bored and honed using two torque plates as an assembly using ARP case bolts and ARP head studs.
VALVETRAIN: Supertech valvetrain package was fitted to this engine after a radius valve job performed. Three angle valve job was performed as well. Valve seat protrusion and flow interference is a big issue on all Subaru engines; particularly intake ports. Our profile three angle valve job does a good job blending seat to port. To finish things off the seats are hand blended to the ports and all casting marks removed. Port velocity is more important than volume 😉 Supertech inconel exhaust valves and stainless steel intake valves fitted in stock size. Supertech dual valve springs and titanium retainer kit installed. Valve spring install heights measured, spring pressures measured, and shimmed as necessary to equalize all valves on intake and exhaust. Kelford camshafts fitted to these heads and camshaft followers adjusted to PRE spec.
LUBRICATION: Killer B oil strainer and baffle plate fitted inside OEM 2007+ STI oil pan. New oil pump is a high volume unit that has been disassembled, cleaned, gerotor clearances measured, casting marks cleaned up, and polished internally. Oil pump primed prior to reassembly with strategic use of thread locking fasteners.