Hey Neckbeards, turbo Subarus don't kill headgaskets (they spin bearings)

Le sigh. It's happened again. Our latest project car, the 4DMILF Subaru wagon, is finally turbocharged and ready to make the kind of power the styling suggested it had... then disaster. CLICK HERE to view the catastrophe.

If your only experience with Subarus is via memes, you'll probably think it's pushed a head gasket. However, the reality with turbo Subarus is the design of horizontally-opposed turbo engines means you're FAR more likely to spin a rod or main bearing. Which is only one step down the list of "Terrible Things You Don't Want Happening To Your Engine" from throwing a rod through the block.

But, why? 

First, in defence of the boxer engine layout these engines have a FAR superior centre of gravity to a conventional in-line four. They are also thought to run smoother and no Subaru engine I've been inside of needs balace shafts (you hearing this, Honda K24 fanbois?)

I've had many turbo EJ-powered Subarus over the years, going back to when I first joined the RS Liberty Club in around 2006 and met Marty, Mechanical Stig, and Turbo Yoda (among many other legends). So I've had my share of blown-up Subarus. 

The bearing issue here comes down to a failure of engine geometry, as well as Subaru loading the dice for those of us who like to add boost to our cars like an American adds cheese to any meal. 

The crank and rod bearings of an engine ride on a tiny, thin film of oil, which keeps everything spinning nicely. When that film of oil isn't there the spinning crank or rod (or both) run metal-on-metal and instantly get super-hot. The risk for any engine at this point is the spinning crank or rod will catch an edge of the bearing, spinning it in its shell and quickly leading to it failing completely. 

These are bearings, for reference.

When a bearing spins in a turbo Subaru you are throwing out the crankshaft, as well as the block, as it is uneconomical to fix the wallered-out surfaces where the spun bearings once lived. So, why does this happen?

Part of the issue is the design of the crankshaft and block, and the forces acting upon them. With a horzintally-opposed cylinder layout there is a huge amount of elliptical rotating stress forced through the rod bearings as they cycle through their travel up and down the cylinder.

The width of the bearings you can fit in a Subaru is another issue. Unfortunately the space on the Subaru crank is tight and this limits the surface area you can run in a bearing and a narrow bearing obviously reduces any margin for accepting issues like detonation, momentary oil starvation, or running over temperature.

Subaru engines are famous for being finnicky with oil quality (cleanliness), grade (viscosity), and level (mildly overfill before doing a lap of a track). If you buy a 2nd-hand Subaru or Subaru engine you're always hoping the previous owner didn't miss a service, used good-quality oil, and ideally drove more long-distance trips than short, 5-minute runs to the shops for fresh bubblegum vapes.

Heat cycles affect engines as the alloy heats and cools, as does the oil. And all of this can have an effect on bearing life - it's often easier on a bearing to do 100,000km up an open highway with almost no load compared to 10,000km of fast trips where it barely gets to temp before being shut down.

While it is a hardware issue, tuning can play a part.

With Subaru's love of running a lot of timing in their factory tunes (possibly to help meet emissions standards) adding boost to the combo begins to really ramp up the pressure in each cylinder. And this dramatically increases stress on the bearings in boxer engines. 

When you boost up a Subaru engine you're increasing cylinder pressure with every additional, delicious PSI you screw into that poor four-banger. This is why many wisened Subaru fans won't push a random engine hard without very careful set-up of the engine combo first, and they understand it is on borrowed time. 

These Subaru engines can be incredibly rugged and make great power, however they're unforgiving and don't blindly accept abuse like other Japanese engines of the 90s/00s. 

If you pull the engine down, check the bearings for wear, and go through every component to set it up to handle a big boost combo from the outset you'll have a lot of fun. If you want to slap an 88mm turbo on a wrecker engine, you're best off playing with a different engine platform, champ.