Your turbo blanketselection should be based on the outer diameter (OD) of the casing on your turbocharger's "hot side" (which houses the exhaust-fed impeller). Therefore, you should either look up or manually measure the diameter of your turbocharger's hot side, as described in the figure below, and purchase the appropriately-sized turbo blanket. PTP Universal Turbo Blankets are tailored to fit turbochargers with external wastegates without any modification. If your turbocharger has an internal wastegate, however, you may need to make a simple modification to allow it to fit appropriately (e.g., cut away a portion of the turbo blanket).