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Subaru Project 1 of 7

TIME TO DECIDE

When Kyle, the owner of this 2005 Subaru found the engine overheating and engine oil/combustion gasses in the coolant, he had a feeling he was going to be replacing the head gaskets. Over the next few months, we’ll be sharing the build story of his 2005 Subaru WRX STi as it's rebuilt to handle serious power, sealed with Fel-Pro® gaskets and put through its paces!

Introduction:

The Subaru 2.5L engine is known to have head gasket issues, especially on the naturally aspirated 2.5L engines with composite OE head gaskets. The 2.5L turbocharged engines are equipped with Multi-Layer Steel head gaskets from the manufacturer, but they can still fail, especially when the vehicle is modified. When you throw performance into the mix, the demands a head gasket must meet change significantly.

Performance engines encounter higher combustion pressure, more casting motion, more cylinder head lift, higher temperatures, higher crankcase pressure and higher potential for detonation than their standard-use counterparts. Performance parts and tuning options are abundant for turbocharged Subarus, so most Subaru enthusiasts modify their vehicles. One of the “easiest” ways to improve performance is to increase boost pressure. However, increased boost pressure increases cylinder pressure, combustion temperature, and the likelihood of detonation. These factors contribute to head lift and casting motion, which can damage the OE MLS head gaskets.

Choosing the right head gasket:

After confirming the head gaskets had failed, Kyle decided to replace the head gaskets, and do a few upgrades while the engine was removed from the car. He also wanted to take a look at the stock head gaskets to find out where and why they failed.

stock-hg-callouts

This is one of the head gaskets from Kyle’s car. The coating at the combustion seal on both cylinders is worn away in many areas. The combustion seal was crushed unevenly on both cylinders as well, with up to .004" variance in compressed thickness, which is a large variance. The traces of carbon between the coolant ports suggest there was combustion leakage in these areas. This is likely due to casting motion and head lift, which wore away the OE coating, and over compressed the gasket.

Kyle wanted gaskets that would hold up against these issues, and to a higher compression and boost.

He chose our 26415 PT PermaTorque® MLS head gasket with LaserWeld™ stopper layer technology. While this particular gasket is not in our performance gasket line, it shares many features with our Performance MLS gaskets making it an ideal candidate for performance Subaru engines. The LaserWeld stopper layer prevents the gasket from being over compressed and reduces the effects of head lift. The proprietary blue coating seals while allowing some casting motion, rather than wearing away.

26416-PT-callouts

The superior primary combustion seal created by the laser welded stopper can hold up to the high cylinder pressures this engine will produce. Also, by precisely limiting the compression of the multiple layers of stainless steel the gasket is constructed from, the gasket will maintain its ability to recover and maintain a reliable seal when head lift may have otherwise resulted in failure.

This concludes Part 1 of this multi-part series in which we’ll follow this vehicle as it is rebuilt. Kyle is keeping us updated through this real-world validation of the 26415 PT head gasket, along with the other Fel-Pro gaskets being used on the vehicle. To see what parts are being installed and what other Fel-Pro products will be installed, check back for Part 2 soon! We’ll introduce the engine builder, cover engine assembly and give a rundown of the engine parts being installed.

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