Article by Brian Hannon. Photography by Corey Davis and Ryan Randels.
As you recently read, we’ve completed modifying the cylinder heads and valve train to make sure the FA20 has sufficient and efficient breathing ability. In this installment, we’re going to pull back the curtain on what was done to modify the cooling, lubrication and fuel/spark systems to withstand the power and reliability we expect to achieve with this build.
We’ve already assessed the capabilities and limitations of this week’s systems so we had a good idea of where we’d need to make improvements. Cooling capacity will be of utmost importance, as the increases in power we’re expecting will certainly result in increased engine heat. The oil and lubrication system also had a few deficiencies, specifically in the oil pan, as we knew we’d need more capacity along with tapping the pan for the turbocharger oil return line. The last item on the list is fuel delivery as our FA20 will be a thirsty beast in addition to keeping up with the new breathing capability of the cylinder heads for our last post.
Now that we’ve reviewed where we could run into issues, lets see what we did to remedy each one.
Upgrading the FA20 / 4U-GSE Cooling System
In order to address the expected cooling issues with the stock radiator, we swapped out the stock unit for a Mishimoto radiator. The new radiator provides increased capacity, improved heat dissipation characteristics, and a more robust design to meet the high heat demands we’ll place on it.
While we’re sticking with the OEM water pump, we upgraded the stock radiator hoses to silicone components to avoid swelling and which can stand up to the heat produced by the turbo that is mounted right near the cooling system.
Upgrading the FA20 / 4U-GSE Oil System
Turning our attention to the lubrication system, we had a mixed bag of areas to address. Thankfully the FA20 already has a very robust oil pump thanks to the needs of the oil-pressure-actuated variable valve timing system. The big issue with the stock system is the complete lack of an oil cooler, a must-have when we get the 500+ horsepower we are looking for. The turbocharged FA20 found in the Subaru Forrester XT now comes with a stock oil cooler, but our normally aspirated version is devoid of one.
The liquid-to-liquid oil cooler we decided to use is from Cusco. It’s hooked into the factory cooling system and allows the factory water-cooling system to do its thing and help keep the water cool. The typical aftermarket choice is an air-to-liquid oil cooler that limits the cooling ability to the temperature of the water-cooling system. With lubrication so important to our high-power engine, we don’t want to present any limitations to its abilities.
In line with keeping the oil cool, we also wanted to increase the systems capacity with a larger oil pan. We’re operating under the assumption that the more oil you have the longer it takes to heat soak. Also, the more oil you have in your pan, the less likely you are to starve the engine. To accomplish this we’re now using a trick Modern Automotive Performance aluminum oil pan that increases oil capacity by a whopping 1.5 quarts!
The MAP pan also has two key features built in: bungs for the turbocharger oil return line and an oil temperature sensor. This means we don’t have to run the risk of modifying the stock pan and it also gives us the opportunity to keep an eye on the oil temperature; very important for our build.
An important note about the pan though is it will not work with the OEM header, and you should confirm with MAP about specific bolt-on turbocharger applications.
Oh, we’re also going to use high-phosphorous, high-zinc motor oil because it helps keep bearings in shape, especially in all the turbo cars. There is also the added benefit of increasing the lubrication properties of the oil itself. Benefits all around!
Upgrading the Fuel and Spark Systems of the FA20 / 4U-GSE
The last topics we’re covering this time are the all important changes to fuel and spark. With our power goal of 500+ horsepower in mind, we designed the system to use E85/E98. That decision was based on the lower propensity for knock, higher effective octane, nice cheap price and availability of the ethanol based blends.
We were faced with some options on the FA20 with regard to how we approached the fuel system since it has a high-pressure fuel system direct injection and a lower-pressure port injection system. The decision was made to keep the direct injection completely stock as there is nothing on the market yet, nor a current need for upgrades.
Instead, we focused our attention on the port-injection since it provides a multitude of tuning options, and a solid base of aftermarket support already exists. Because we want to use E85/E98, we must compensate with more fuel because the stoichiometric ratio is different; it takes more fuel to reach the 14.7 air-fuel ratio. To make sure the engine is provided with enough fuel, we’re upgrading to Injector Dynamics 1000cc injectors and a higher-capacity, low-pressure fuel pump, the 265 lph DeatschWerks DW65C series pump, to meet the demands.
To ensure we have consistent combustion on every stroke, we’re also upgrading the spark plugs to a set from HKS racing. The plugs are one step colder than factory so we have an added level of protection against knock.
That puts a wrap on fuel, lubrication and cooling. Some of the improvements we made may be a bit overkill, but we wanted to leave ourselves a wide margin of safety with tuning potential and every day driving. Next up should be one of our most anticipated posts as we detail the turbo kit produced by AR Design. Absolutely amazing is an understatement! Stay tuned!
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