Ok, thanks! Reason I'm asking is that according to the book "How to tune & modify your Ford 5.0-liter Mustang" by Steve Turner, it says regarding cylinder heads "stepping up to the 2.02 intake valves mandates moving to aftermarket pistons notched for proper valve clearance; this is easily accomodated at rebuild time..." I was a bit surprised to read this as I thought most aftermarket heads even with 2.02 valves were basically bolt-on.
I havent decided on heads yet but the AFR 185 is one I'm considering, hence just wanted to check with you people.
IF you havent bought yet.. DONT go that big with a small cam!! stock pistons are made for the 1.85 intake valve size, even a 1.90 is out of the pocket and has touched the piston!! why go that big when you are staying with a small camshaft.. you COULD actualy slow down!! With a small or stock camshaft the smaller heads will build more power !! Just a thought .. and ALWAYS check p/v when you install the heads or the bigger camshaft!! Cool?
Ok, thanks! Reason I'm asking is that according to the book "How to tune & modify your Ford 5.0-liter Mustang" by Steve Turner, it says regarding cylinder heads "stepping up to the 2.02 intake valves mandates moving to aftermarket pistons notched for proper valve clearance; this is easily accomodated at rebuild time..." I was a bit surprised to read this as I thought most aftermarket heads even with 2.02 valves were basically bolt-on.
I havent decided on heads yet but the AFR 185 is one I'm considering, hence just wanted to check with you people.
Only two cylinder heads with 2.020 intake valves are able to clear stock pistons. Trick Flow Twisted Wedge and Canfield 170 street heads. Even then, it's still a "must check" for piston to valve when you install them.
What most people don't realize is the radial clearance gets very close or hits the valve reliefs, even when small camshafts are used. Vertically there is room but when the pistons rock, heat expands the parts.... well.... $hit happens...
Also..
If this is for the forced induction KB combo... The AFR 185 heads are a perfect choice. Plenty of exhaust flow and a great intake port for mucho boost... Just check P/V and get ready to fly cut...
You know guys its not so much how big the valves that are the issue. Its duration. When the piston is at the top of the cylinder if a valve is still open is when the issue of clearence becomes just that an issue. If however you have a stock cam with out a major amount of duration the valves are closed and there is no issue. Still i would bolt the head on huck a chunk of plastercine in the cylinder and rotate engine by hand. I would have head installed with no head gasket to make up the difference of the lifter being pumped up. then check the plastercine for the mark of the vavles and mesure the thickness.
You know guys its not so much how big the valves that are the issue. Its duration. When the piston is at the top of the cylinder if a valve is still open is when the issue of clearence becomes just that an issue. If however you have a stock cam with out a major amount of duration the valves are closed and there is no issue. Still i would bolt the head on huck a chunk of plastercine in the cylinder and rotate engine by hand. I would have head installed with no head gasket to make up the difference of the lifter being pumped up. then check the plastercine for the mark of the vavles and mesure the thickness.
You are right about the duration being the key to P/V issues but the valves are not closest to the piston at TDC. They are ususally closest anywhere from 5* to 15* away from TDC.
There is also the "edges" of the valve heads in relationship to the piston top/relief and how they are configured in the head that plays a role...