Koyo R-Core Radiators are the thickest Koyo Radiators on the market. Koyo R-Core Radiators are used for when cars need extreme cooling. Upgrading your Turbo? R-Core. Front Mount Intercooler hogging the flow of air? R-Core. Although Koyo R-Core Radiators are thicker then stock, they will bolt it and fit like OEM with no modification.