Once all of the pieces were cleaned, inspected, machined, weighed and balanced it was time to get down to nuts and bolts.  There was one more measurement that is very critical to a Subaru engine. This is the fit of the piston to the cylinder wall. From the factory this measurement is .0004. To put it into words, it is less then one half of one thousandth of an inch. To visualize it: take a hair from a blonde (they are about .003) split it lengthwise in half (.0015), and then in half again, (.000525). That is almost how tight the pistons fit from the factory. By comparison most chevy engines are made with a tolerance of over one-half to two thousands brand new. Two thousands clearance is where Subaru suggests you rebuild their motors. Of course I did not make our engine as tight as factory. There is a fine line between too tight where a race motor will seize and too much where you hear the pistons slap and or burn oil.

One observation about the Subaru engine block. For such a short engine, Subaru employs 5 main bearings. This makes the block ridged and keeps the crankshaft from twisting. This is a very solid engine from the factory. No wonder it is the engine of choice for many small aircraft builders. Even the oil pumps are drilled and tapped for a dry sump oiling system!


The case halves are  ready to assemble. There was at least three separate washings they go through. The last one is by  hand with hot soapy water. The rods are bolted to the crankshaft first and the case halves are bolted together. Once the case halves are together and pistons installed, the hard part is done. All the thinking and planning on the critical insides is complete. It is just another hour or two to put all the externals on. We did upgrade the oil pump to a high-volume STi unit. Subaru dealers usually have these on the shelf. We also used a closed impeller water pump found on some models of Subaru. When it is all together, it looks like an average 2.2 liter engine, except it’s not.

When I first fired it up, there was a loud clattering from the head area. It sounded like valves hitting pistons. Immediately the heads were pulled back off to see what was going on. I was correct. About half the valves were just nicking the piston tops. I had not factored in the shaving of the heads—we had .015 in. removed from the surface and also the ceramic coating added a little height to the pistons. I had no choice but to install the thicker, stock 2.5 DOHC gasket, thus lowering my gains a little on compression. 

INCOGNITO: Race motor installed back under the hood, looking like the factory engine.

SHAKEDOWN:  Days later, Paul is on the Oregon coast, pushing it hard, trying to find any weak spots.

I have never been into expensive chrome or anodized brackets if it does not add horsepower. If the reader is familiar with the stock arrangement on the left, I am sure there are questions such as. “Why the stock air cleaner?”

Or “ air conditioning?”

And if you can see underneath: Why a cat convertor?”

I will explain some of this in Part Three. Next Page . . .

Engine Oil


Paul also switched the oil over to full synthetic engine oil as it can withstand much hotter temperatures before breaking down. Petroleum-based motor oils are extremely sensitive to temperature changes, and the less refined the oil is, the more quickly it will succumb to thermal breakdown. Conventional oil can degrade between 250-275 degrees. The surface tension (viscosity) of the oil breaks, allowing metal to metal contact. Synthetic oil can get to 400-450 degrees before this happens. Synthetics also do not sludge like petroleum oils.


The engine’s main and rod bearings are only a smooth soft shell of metal that is separated from the spinning crankshaft by a very thin film of oil. As the shaft rotates, it pushes a wall of oil before it and rides on this high pressure ridge of oil in front of it. The oil, in reality, is the “bearing” that does all the work. If the oil gets too hot it goes through a chemical/molecular breakdown allowing the two metal parts to touch. In a matter of seconds, an engine can start knocking or seize altogether.


Dirt, sludge, heat and oxidation are oil killers. Oxidation will naturally happen over time, however, an excess whipping of the oil in the crankcase speeds this up. It just so happens that Subaru, by design has its crankshaft well away from the oil in the pan and includes a windage tray in every engine they build.  


All the prep work we could think of was done, synthetic oil, a stock water-to-oil cooler from a Forester, an external air to oil cooler, ceramic coating and a high efficiency radiator. How did it work? For four grueling days, Paul pushed it to the limits with the AC on high in 100+ degree heat. Even climbing some very high mountain passes. Complete evaluations in part 3.

More on Cooling

I pondered the radiator quite a bit as it is the main mechanism to cool our 2.5 engine in the 100+ heat of April in Mexico. It was a single row aluminum radiator from the factory. I asked different parts suppliers and found that there are no two or three row, aftermarket or OEM radiators made for the lowly Subaru. For enough money, one could have a custom unit made, however, if you examine any Subaru radiator closely, you will see the fins are stacked very closely together. This makes any radiator high efficiency. So Subaru makes a very adequate radiator for hot conditions on their production cars. We left it alone as with the stock thermostat.



It is a mistake for a rookie engine builder to assume that an engine will run cooler if you take out the thermostat. Initially it does and it is a trick to keep an engine cooler if a head gasket is blowing. However, a thermostat not only allows an engine to warm up quickly (essential for computer controlled engine management) but it also slows down the flow of coolant giving it a chance to move through the radiator slow enough to actually cool down. It is not unheard of to see a race engine overheat due to a missing thermostat! Some racers install a restrictor in place of a thermostat to make sure a thermostat never sticks yet slows down the flow of coolant.

First Impressions

The first test drive around Vancouver was very satisfying. The power from a stop was about the same as a stock Outback but as the car gained RPM and speed, the torque kept increasing. To me it felt like a stock turbo. We did not bother to spend the money on a dyno test, so we cannot brag about horsepower. The more important question, does it have the torque at the speed you need it? 


The next test was to try and replicate conditions of the Baja Peninsula. Paul lives in Tillamook County, Oregon, right next to beaches and mountain fire roads which would do just fine for a serious shakedown.


I told Paul not to baby the engine but to drive it as if he was in the race, almost to the point of wanting to break it. If something was wrong I wanted to know in the next couple of months. Paul did as instructed, driving it hard on the way home and over the next few months taking it out on the sand hills and deep into the Tillamook mountain range.

The Making of a Winner: Building Paul Fournier's Mexican 1000 Subaru Power Plant.

Sept-Dec. 2012