The latest version of Chrysler’s “A” engine block features a different
lifter bore angle. This block is commonly called the “R” block. The
angle of the lifter bore is changed to help straighten out the
pushrod angle. The standard lifter angle on the “A” engine is 57
degrees from vertical. This points the lifter away from the center of
the block and angles the pushrod toward the outside.
Most of the
“R” blocks and some highly modified versions of the “A” engine
have a 48 degree lifter angle. This points the lifter more directly at
the rocker arm and helps to eliminate deflection at very high
engine speeds. No standard production blocks were made with this
modification, so if your block is not a special “race only” part from
Chrysler, you probably have the 57 degree lifter angles. These
cams are not interchangeable, so it is important to note the lifter
bank angle prior to ordering any racing cam. If no special lifter bank
angle is stated, the standard 57 degree cam will be used.
The same changes are common on some of the newer aluminum
aftermarket Hemi blocks, the difference being much more subtle,
from 45 to 48 degrees. It is extremely important to make sure
which lifter angle your block is machined for prior to ordering a
cam. As with the small block, if no special lifter angle is requested
the cam will be ground as with the standard 45 degree lifter angle.
–Tech Tip courtesy of Comp Cams.
