The stock valves are used because they are good quality and can take the abuse of a turbo engine.
Stock springs are also used and will do fine with stock cams even over 7000 RPM. Upgraded springs are recommended with larger cams. Because the stock valves have such a small diameter, I cannot do them myself. A local machine shop does a great quality valve and seat job for a good price. PT Lifters are also a good upgrade, but are somewhat expensive.
