Reply to "Seeking advice on camshaft selection"

I have always been in favor of the small incremental improvements in camshaft lobe grinding technology that have occurred over the last several decades. Higher lift for a given amount of duration equals more power with a 351C 4V. I thought the fast ramp rate of the lobes employed for the Comp extreme energy cams or Lunati voodoo cams were a cool way to use tighter lobe separation without incurring excessive overlap (overlap quickly diminishes the drivability of a 351C with 4V heads). True, there was less overlap for a given amount of lobe separation, but due to the lobes' short ramps (smaller hydraulic intensity numbers) it doesn't take as much overlap before the cam starts inhibiting the drivability of the motor. So there really is nothing to be gained in using such camshaft lobes.

There are several drawbacks however. The lobes are too aggressive for a flat tappet hydraulic cam; they increase the likelihood of developing hydraulic lifter problems, they increase the likelihood of developing valve train instability problems, and they will float the intake valve at lower rpm. Camshafts employing those lobes open the exhaust valves too late, putting a greater emphasis on the requirement for a low back pressure exhaust system, otherwise the motor's power band will flatten-out too early at upper rpm. In general the XE & VooDoo cams do not rev as high as the manufacturers claim. The lobe separation angles are generally too narrow for a motor equipped with 4V heads too.

So I stopped liking (or recommending) the Comp extreme energy cams or Lunati voodoo cams a few years ago and went back to what I know works. A cam with 112° to 114° lobe separation and about 60° of overlap (based on advertised duration) will give you the combination of drivability and lopey idle you're seeking. 112° lobe separation with 4V heads is equivalent to 108° lobe separation with a small valve motor. Look for a cam that opens the exhaust valve around 80° BBDC and closes the intake valve around 70° ABDC. The intake valve should close no later than 40° ABDC based on duration at 0.050".

Other criteria useful in judging street cams: the overlap based on advertised duration should not exceed the hydraulic intensity of the lobes; and centering the overlap period around top dead center is beneficial, especially with big valve (4V) heads.

These days the off-the-shelf cam I recommend most often for a motor with 4V heads is the Crane Cams Grind no. H-278-2 (part number 523801).
--------------------------------
278°/290° advertised duration
222°/234° duration at 0.050"
0.539"/0.534" theoretical valve lift
114° lobe separation angle
Hydraulic intensity 56°/56°
---------------------------------
Exhaust valve opening = 80° BBDC
Intake valve opening = 26° BTDC
56° overlap
Exhaust valve closing = 30° ATDC
Intake valve closing = 72° ABDC
---------------------------------

Of course, in sticky number 3 of this forum I've provided a whole bunch of info on the subject of cams and valve train.

-G