Project Gen 3 Subaru STI: Keeping it Cool with Koyo
By Mike Kojima
While awaiting the development of some ARK parts for our Project 3rd generation STI we decided to prep the cooling system in anticipation of the future installation of power parts. Turbo cars run hot and when being track driven most have problems staying cool, especially on our Southern California tracks which are mostly located in the desert.
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| The Koyo radiator is high quality, tig welded, and all aluminum in construction. The one piece construction can take way more pressure than the stock part. It is a high fin density double row design. |
We turned to Koyo Cooling systems for one of their race radiators for our car. The stock Subaru radiator is a single row heat exchanger with plastic tanks and an aluminum core. The core is 16mm thick.
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| You can see the Koyo radiator's aluminum end tanks compared to the two piece crimped on plastic end tanks on the stock radiator. You can also see the mounting pegs and the fan mounting tabs to fit the factory parts. |
We replaced the stock radiator with Koyo part number VH13093. The Koyo radiator is all aluminum in construction with tig welded end tanks. It is a high fin density double row design 36mm thick, more than twice the thickness of the stock part. The Koyo radiator had a ¼” NPT fitting near the inlet pipe for the mounting of a temperature sensor or a vent for a surge tank. The radiator was a direct bolt in and fit well with the factory fans exchanging perfectly.
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| The Koyo radiator is 36mm thick, more than twice the thickness of the stock part. It has two rows to the stock single row for way more cooling area. |
To test the radiator, we used an ARK MFD II to record the engine temperature at idle while warming up and during a loop we drove on the freeway to assess the cooling effectiveness. We came up with the following data.
