Our 272° camshaft is built to collaborate with the OEM valve springs and will cause a rough idle with the exhaust upgrade. If you're looking to upgrade the turbo, then the compressor inducer should be between 48-58mm. Utilizing MIVEC will lead to a broader power band and enhanced throttle response. For high mileage engines it is recommended to replace valve springs with the KVS63-BTK kit. Finally, upgrading the turbo will result in an increase in mid-high rpm power.