Guys how much lift can you have on the stock iron GT40 heads? Did the cobra GT40 heads have beefier valve springs? I have been told that the valve springs are rated for .550 max lift is that right?
Guys how much lift can you have on the stock iron GT40 heads? Did the cobra GT40 heads have beefier valve springs? I have been told that the valve springs are rated for .550 max lift is that right?
