I didnt fit them my buddy did so not sure if they need shimming? Tbh I wasnt aware they'd need to be shimmed I thought they would be just bolt on and go! I fitted two NOS jets one in each pipe as we had to try find a solution quickly! Pressure did increase but not as much as we need! isnt the golden rule 10psi per 1000rpm? Do I need to shim these rockers or just downsize the NOS jets more?