Caterham....anyone?

I am surprised that the engine feels weak below 5000, the r500 Duratec is usually really tractable. You can tootle along at low speeds with no issues, the flexibility is one of the great things about that engine (unlike the 1st generation r500). Cam centers should be at 108 intake, 106 exhaust; you should probably check them or have them checked. Also, you need to make sure you have an oil pressure relief spring.