Reply to "hydraulic cam for 2v heads"

Hydraulic roller valve train having the same capabilities as a flat tappet valve train requires more valve spring force, and of course that means in the long run a faster wearing valve train. Hydraulic roller valve train is more expensive. Hydraulic roller tappets operate with a tremendous amount of side thrust friction that is not found with flat tappets. Using roller tappets does not mean the motor can use any oil, because the distributor drive gear still needs ZDDP.

In regard to the angst that exists regarding flat tappet cams and premature lobe wear, my best advice is to never make a decision based on fear, that's irrational. I go round and round with younger guys debating this issue. In their minds there is some mysterious force at work that makes flat tappet cams fail unpredictably. But decades ago we installed flat tappet cams in our motors and never thought twice about the possibility of premature failure. If flat tappet cams fail prematurely today there is an understandable explanation for this. I think it must boil down to either (1) an oil issue (lack of ZDDP); (2) a QC issue, i.e. the parts were not made of the same materials used decades ago or were not heat treated properly; or (3) a performance issue, meaning the flat tappet lobes of our street cams today have faster lift rates, require more spring force, and therefore wear like race cams did decades ago. So my solution is (1) to use the right oil, (2) to custom order the cam requesting the cam grinder's best heat treating and best lobe polishing, and to use the best lifters possible, and (3) to avoid using the highest lift rate camshaft lobes or excessive valve spring force. Taking those steps should get a person a cam that is at least as durable as the cams we purchased off the shelf decades ago.

In regards to performance, comparing the profile of a hydraulic roller tappet lobe with the profile of a hydraulic flat tappet lobe both having the same advertised duration, the hydraulic roller tappet lobe will have less duration at 0.050” but more valve lift. We can make a powerful motor with either type of camshaft, the hydraulic roller cam simply substitutes valve lift for duration at 0.050". Lifting heavier valve train components (i.e. the roller lifters) faster and higher is the reason the hydraulic roller cam tends to negatively impact the high rpm capabilities of a motor. I do not consider the hydraulic roller tappet as having more potential than a hydraulic flat tappet in a street motor application. Ultimately both technologies have limits, increasing flat tappet duration will hurt drivability, but increasing roller tappet lift requires more and more valve spring force with an increase in the rate of valve train wear.

I go back and forth in trying to decide which type of cam to install in my next motor. Although I like roller cams, I think today's hydraulic flat tappet camshaft lobes offer the better balance between lift and duration. I believe that balance is exemplified by the 3 Cleveland friendly hydraulic flat tappet grinds I offer to folks.

Cobra Jet camshaft
Grinder: Bullet Cams
Intake: Lobe #H275/318
Exhaust: Lobe #H285/324
-----------------------------
275°/285° advertised duration
280° average duration
Exhaust valve opening = 80° BBDC
Intake valve opening = 25° BTDC
50° overlap
Exhaust valve closing = 25° ATDC
Intake valve closing = 70° ABDC
------------------------------
225°/235° duration @ 0.050
0.550"/0.560" valve lift
115° lobe separation angle
Int lobe mathematic centerline = 112.5° ATDC
Ex lobe mathematic centerline = 117.5° BTDC


Boss camshaft
Grinder: Bullet Cams
Intake: Lobe #H285/324
Exhaust: Lobe #H295/324
-----------------------------
285°/295° advertised duration
290° average duration
Exhaust valve opening = 85° BBDC
Intake valve opening = 30° BTDC
60° overlap
Exhaust valve closing = 30° ATDC
Intake valve closing = 75° ABDC
------------------------------
235°/245° duration @ 0.050
0.560"/0.560" valve lift
115° lobe separation angle
Int lobe mathematic centerline = 112.5° ATDC
Ex lobe mathematic centerline = 117.5° BTDC


¾ Race camshaft
Grinder: Bullet Cams
Intake: Lobe #H285/324
Exhaust: Lobe #H295/324
-----------------------------
285°/295° advertised duration
290° average duration
Exhaust valve opening = 81° BBDC
Intake valve opening = 34° BTDC
68° overlap
Exhaust valve closing = 34° ATDC
Intake valve closing = 71° ABDC
------------------------------
235°/245° duration @ 0.050
0.560"/0.560" valve lift
111° lobe separation angle
Int lobe mathematic centerline = 108.5° ATDC
Ex lobe mathematic centerline = 113.5° BTDC

The 3/4 race cam is simply the Boss cam with narrower lobe centers. It offers a lopier idle, less manifold vacuum, a narrower power band, but a steeper torque curve and higher peak numbers. It may get you around a track (on track tires) faster, but on the street or a winding mountain road I would prefer the boss cam.

-G