Tial BOV Spring. Made by Tial and used to change out the spring pressure on the Tial 50mm BOVs (and copies) to affect the BOV response tuning to reduce comprssor surge (different spring levels affect amount of vacuum required on each engine to open the BOV on throttle release) Spring Colour PSI Vacuum Bar Vacuum Black 7 0.5 White 9 0.6 Unpainted 11 0.75 Pink 12 0.8 PLEASE NOTE: These are selling very quickly, so from time to time we run out of stock... It *may* take 4-5 days for you to receive your spring, but we will let you know when you order.