Alright im posting this one for my dad so he will put this motor togeather and get his Tiger on the road..He has a 302 with a new set of AFR heads and comp cam rocker arms, he is wondering what lenth rods he needs. any ideas?
Each motor should be checked for proper pushrod length and valve train geometry with a pushrod-length checker. You didn't mention anything about the camshaft -- BIG variable in pushrod length. We don't know if it's a roller 302, flat tappet, solid, hydraulic -- no way of knowing what kind of cam is in it. If it's an HO roller motor - with a stock hydraulic roller base circle cam he'll probably be ok with stock HO length pushrods -- but he should mock it up with a pushrod length checker -- and THEN he'll know what length he needs.
The 'size' of the cam (duration or lift) isn't so much the issue as the base circle it's ground on. The other thing that should be checked is the geometry -- how the rocker is hitting the valve stem tip throughout it's range of motion. Ideally you want the centerline of the rocker tip sitting right in the middle of the stem tip when the valve is open to mid-lift. That approach will maximize lift and minimize side-loading of the valve stem throughout the rocker's range of motion. That geometry can be adjusted by altering the position of the rocker (height and placement on the head) and the pushrod length. Those detailed dimensions differ from engine to engine and ideally should be checked so that the parts ordered will achieve the desired result. As Rick alludes to above -- with the parts we're talking about here -- they usually come out pretty close to stock. But assuming that without checking will occasionally cause problems.