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Subaru Project Part 2 of 7


In Part 1 of the Subaru project, Kyle verified that the factory head gaskets had failed on his 2005 WRX STi. He decided to use Fel-Pro® PermaTorque® MLS head gaskets (and other Fel-Pro gaskets, which we’ll cover in Part 3) for the rebuild.

Right now we’re going to look at the prep work and assembly, along with the components used to rebuild this engine. As we’ve mentioned before, even the best gaskets can’t seal without the proper sealing surface prep or when improper components are used. Fortunately that won’t be an issue in this case – between professional machining and assembly, high-quality parts and Fel-Pro gaskets to seal it all, this engine will be up to the challenge.


The machining and assembly of the longblock was handled by Moore Performance, located just outside of Pittsburgh, Pennsylvania. Kyle chose to work with Moore Performance on this project because of their expert knowledge, experience and excellent reputation in the Subaru community. The team at Moore Performance have been Subaru owners and enthusiasts since the first WRX came to the United States in 2002. With many 500+ WHP Subarus under their belts and a shop record of 730 WHP so far, Kyle knew working with them would ensure his engine was built right.

Engine Block:

Kyle didn’t use his original engine block, but instead used a core from another 2005 STi. This block was cleaned, machined, and cleaned some more. The sealing surfaces of the block were decked square to the cylinders and finished to a perfectly flat, ultra-smooth finish, ideal for sealing with MLS gaskets. A torque plate was installed while the cylinders were honed to simulate clamp load and bore distortion from the cylinder head being torqued down. This results in less blow-by and oil consumption, and reduces wear to the cylinder walls and piston rings.

With the block properly prepped, let’s take a look at what’s inside. A new, heat-treated crankshaft, H-beam forged connecting rods and 8.9:1 compression ratio forged/hard anodized pistons make up the rotating assembly. This combination was balanced to 9000 rpm (although the engine won’t be pushed that far) so it’s ready to handle anything that’s thrown at it.

The original cylinder heads were completely reworked for this project. They were milled to 15Ra, which falls well below our max specification of 60Ra for PermaTorque® MLS gaskets. A full-contour valve job was done to accommodate the stainless intake and Inconel exhaust valves, and the valves were back cut to improve flow. The valve guides were replaced, and performance spring locators and shims were installed. Upgraded valve springs and titanium retainers were chosen and the installed height was adjusted and set. New shimless buckets and valve tipping were used to set the valve lash for the aftermarket camshafts.


Other Components:

A new oil pump, oil pan, oil cooler, upgraded aftermarket oil pickup tube and windage tray were installed to help prevent oiling issues. A new water pump and thermostat were installed to help keep things cool. All-new timing components and a Kevlar-reinforced timing belt will ensure timing is spot-on. Finally, a vibration-dampening crank pulley was installed even though the rotating assembly was balanced.

Head Studs vs. Head Bolts:

Kyle opted to use head studs instead of head bolts, as many people do on performance applications. Studs are threaded into the block and don’t “twist” as they’re being tightened like bolts since only the nut is tightened. This allows much more accurate torque values to be achieved. Because the studs remain stationary during nut tightening, the studs stretch in one axis alone, providing more even and accurate clamping force. Studs also result in less wear to the block’s threads, which extends the life of the threaded holes in the block over periods of servicing/rebuilding.

While Fel-Pro head gaskets are designed to make the best use of the clamp load provided by the OE head bolts, they will work just fine with head studs. The fastener manufacturer’s torque specifications must be followed if head studs are used. In this case, the head studs are torqued to 100 ft-lbs in 3 even steps. The increased clamp load from the head studs adds to the already excellent combustion seal created by the LaserWeld™ stopper layer to create a seal that can stand up to the increased compression and high boost levels this engine will see.


So, just to recap – we have high quality components, precise machine work and professional assembly by Moore Performance, PermaTorque MLS head gaskets as the solution to Kyle’s concerns about other head gaskets and an assembled longblock. Kyle picked the longblock up and is dropping it into the car, meaning that’s all for Part 2 of the Subaru Project. We’ll be back soon with updates and will talk about some of the other Fel-Pro gaskets that will be sealing this engine, so check back soon!

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