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Subaru Part 4 of 7

Back to the Drawing Board

When we last talked to Kyle in Part 3 of the Subaru project, he installed the engine and got the car running. After confirming there were no leaks, he trailered the car from Cleveland, OH to his tuner in Buffalo, NY to get a safe tune for engine break-in.

Unfortunately, things don’t always go as planned. After running into a few issues on the dyno, Kyle trailered the car home to sort things out. The tuner was able to provide a safe tune so that the car was drivable, although it was not a high-power tune. The primary issue was that the engine was prone to detonation. The exact cause was unknown at the time, as the components and fuel used were properly matched, and the detonation was erratic.

Detonation, also called knock or pinging, greatly increases the temperature and pressure in the cylinders and can result in severe damage to internal engine components and head lift. All of these conditions are tough on head gaskets – Kyle was glad he chose to use Fel-Pro® gaskets in place of the OE gaskets.

Fel-Pro PermaTorque® MLS head gaskets are engineered to stand up to these extreme conditions. The LaserWeld™ stopper layer incorporated into the 26415 PT gaskets offers the strongest combustion seal available. LaserWeld also prevents over-compression of the embossments, allowing these gaskets to maintain their seal even with the high cylinder pressures encountered in this engine.

The engine was also stumbling between 2000-3000 rpm. There were many things that could have caused this, and the tuner made some suggestions which included adding additional grounds, adding dampers to the fuel system, changing the MAF sensor, and replacing the crankshaft sprocket/reluctor. Kyle did all of these, along with trying a few other things he read about on the Subaru forums, but the stumble persisted.


Having tried everything he could, Kyle scheduled another appointment with the tuner. They figured it would be worth trying to tune the car again with all of the components that were swapped out to see if the issue could be corrected. Much to their dismay, the stumble was not able to be tuned out and detonation was still an issue. The car wanted to make power, but they decided it was best to run a low boost, reduced timing and rev-limited tune. The car did make 351 all-wheel horsepower at 17psi, which gave them hope for solid power at their goal of 23-24 psi!

The car did run well enough to be drivable, and Kyle put just over 2200 miles on the built engine throughout the summer. He even brought it up to the Federal-Mogul Motorpart’s headquarters in Southfield, Michigan for a car show we invited him to! Kyle continued to search for a solution to his drivability issues, and finally found information on the Subaru forums that gave him a lead! Two other members of the forum had very similar issues in the past, and the “common denominator” between all three builds were the same part number set of aftermarket camshafts. After sharing this information with his tuner and engine builder and discussing their options, Kyle opted to change the camshafts.

Changing the camshafts meant that the spring installed height and valve lash would need to be adjusted, so the cylinder heads were removed and inspected for damage from detonation. Kyle sent the old head gaskets to us so we could analyze how they held up to the extreme conditions. After careful inspection by our Performance sealing engineers and John Gurnig from the Fel-Pro Field Test Garage, the results were in:


Aside from some carbon buildup at the combustion seals and some dried coolant on the surfaces (from cylinder head removal) the gaskets looked practically new! They not only sealed combustion pressure, coolant and oil as they should have, but also stood up to extremely high cylinder temperatures and abnormally high pressure from detonation. Had the heads not been removed to go back to the machine shop, these gaskets would have continued to seal perfectly!

This concludes Part 4 of the Subaru Project! In Part 5, we’ll learn what changes Kyle made while the engine was out. He told us he was going to push the engine further than originally planned on the new and improved setup, so we provided him with a set of prototype, 5-layer Performance MLS head gaskets that we had recently finished validating in our lab. These Fel-Pro Performance prototype gaskets feature a high-temperature performance black coating, 3 active layers (compared to 2 on the standard gasket), a thicker shim layer to compensate for cylinder head and block material removal during machining, and a thicker LaserWeld Stopper layer for the ultimate seal under high boost. Check back soon for more information, to hear what the engine builder thought of the prototype gasket (spoiler alert – they’re excited!) and to see what changed on the build. See ya next time!

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