Mmmm, I have 1.7 rr's on my GT-40 heads and have always had a tick since I installed them. I have talked to others who say the same, so I just kind of passed it off as normal.
I almost hate to even post this, as I am afraid I know the answer. But, when we put in my 1.7 rr's about 3 years, the guy just installed them and said they didn't need shims. I don't know if this is right, but I trusted him. He runs a mid-8 second Mustang himself and seems to know his stuff. Hope I am not doing any damage not having any shims installed
