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Subaru EJ22T stroker engine using D25 EJ255 cylinder heads for 2005 STI

BACKGROUND

This engine we designed and prepared for a Subaru customer in Florida. Engine will be fitted to a 2005 Subaru Impreza STI.

PARTS AND SERVICES

ENGINE BLOCK: Engine started out as an EJ22T closed deck block. 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 and main bearings.

CASE BOLTS: We use OEM case bolts for this engine. Block bearing housings were checked using stock bolts. The block was align honed to size.

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 and a bowl blend. Radius valve job was performed because valve seat protrusion and flow interference is a big issue on all Subaru engines; particularly intake ports. Radius 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 important! 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. GSC S2 billet camshafts fitted to these heads and new camshaft followers adjusted to PRE spec.

LUBRICATION: Killer B oil strainer, oil pan, and baffle plate fitted. New oil pump is a high volume unit that has been disassembled, cleaned, gerotor clearances measured, pump primed prior to reassembly with strategic use of thread locking fasteners.

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2 thoughts on “Subaru EJ22T stroker engine using D25 EJ255 cylinder heads for 2005 STI

  1. How many miles are on this build and what kind of numbers is it putting down? Also, what is the static conpression ratio for this build? Lastly, what is the maximum miles this EJ22t + EJ255 head (intake avcs) can last if you keep wheel power below 400hp?

    1. Thank you for the interest. We have not heard updates from this customer about the progress of installation or tuning of this particular engine. We have built quite a few of these EJ22T blocks with various cylinder head combinations including EJ205, EJ255 D25, EJ257 B25, and EJ257B W25. The most recent engine was an EJ22T/W25(dual AVCS) combination for a 2008 STI with a rotated GTX3076R Gen2. AT 30psi boost the car made 610whp. That car was built for road course racing and so far ran at Gingerman Raceway, Autobahn Country Club, National Corvette Museum, and Road America. The engine has 5000 miles and runs exceptionally well.

      Our custom pistons are built to have a static compression ratio of 8.2 when using 25, V25, or W25 cylinder heads. If you use the D25 cylinder heads, with the smaller volume combustion chambers, you will have roughly 8.6-8.7 compression. This also depends on your head gasket choice. If you want different compression ratio, we offer made-to-order pistons.

      If you are keeping power levels below 400hp, you don’t need an EJ22T block. It would be a waste of a rare block. Your requirements can easily be met with a conventional EJ255 block prepared with forged rods and pistons. We have a large inventory of EJ22T blocks but we only sell them to be used for the ‘big power’ or road racing projects. If you supply your own EJ22T block, we can perform this same type of preparation service.

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