[Steve C.]

'Roller Pressure Angle'

The direction of the applied force lifting a roller lifter is at an angle and not directly along the axis of the lifter. The more aggressive the profile, the greater the pressure angle. Beyond the limit at about 33 degrees, reliability drops dramatically. This side thrust distorts the lifter body and leads to hydraulic collapse. These side loads are not seen with a flat-tappet-style lifter hence the problem is not an issue. The bigger the roller and cam base circle, the less the roller side loading

On a Pontiac application you will often see it touted that a lifter bore brace is typically not necessary until the duration at 0.200" valve lift approaches or is over 200 degrees duration. But even if their roller cams don't follow that guideline many go ahead and install them anyway as insurance

Of interest.... years ago Jim Butler included a list of solid roller cams offered in his catalog (they were Comp Hi-Tech .420 rollers), and with that listing of cams he mentioned specific lobes that he stated "should not be aggressive enough to break lifter bores". Those lobes were from 252 at .050 (169 at .200) thru the top lobe with 282 at .050 (195 at .200).


.