Reply to "Solid Flat Tappet Street Cam"

Rich posted two cam specs.

The first spec:

Grinder: Bullet Cams
Intake: Lobe #F285/355
Exhaust: Lobe #F295/358
115° lobe separation angle
Intake lobe mathematic centerline = 112.5° ATDC
Exhaust lobe mathematic centerline = 117.5° BTDC
-----------------------------
285°/295° advertised duration
250°/260° duration @ 0.050
0.585"/0.590" net valve lift (0.029" lash)
------------------------------
Exhaust valve opening = 85° BBDC
Intake valve opening = 30° BTDC
60° overlap
Exhaust valve closing = 30° ATDC
Intake valve closing = 75° ABDC

Today I would change this cam by using a 290° exhaust lobe (the best matching lobe I found is #F292/354. 292° advertised duration, 255° duration at 0.050, 0.586 net lift at 0.026 lash).

Curious why? Because we never really need more than 290° exhaust duration. And by shortening the exhaust duration I can "tighten" the LSA without increasing overlap. I'd move the exhaust centerline to 115° BTDC, and move the intake centerline to 113° ATDC. That narrows the LSA to 114°, 99% of my cam are 114° LSA these days.

The second spec:

Grinder: Bullet Cams
Intake lobe #FF280/371
Exhaust lobe #F292/373
Lobe separation angle = 112.5°
110° ATDC intake lobe mathematic centerline
115° BTDC exhaust lobe mathematic centerline
---------------------------------------------
280°/292° advertised duration
251°/263° duration at 0.050"
0.620”/0.630” net valve lift (0.022/0.019 lash)
---------------------------------------
EVO = 81° BBDC
IVO = 30° BTDC
Overlap = 61°
EVC = 31° ATDC
IVC = 70° ABDC

Today I'd move the intake centerline to 111° ATDC, making the LSA 113°. I just don't get so fussy as to specify 1/2° LSA or lobe centers any more. Chalk that up to old age. But on the positive side overlap decreases by 1°. The first cam has lobes with longer ramps and would make the better street cam. The second cam is definitely more of a race cam (short ramps and more lift). Its definitely going to push the cylinder walls of the production block to their limits under racing use. On the positive side the 70° IVC means you won't have to run a bunch of static compression, the engine will get by with 10:1 and 91 octane fuel. Both cams will give an engine Boss 351 type low rpm performance, yet peak horsepower is going to occur ~ 7000 rpm. Tanti Cavalli! That's the beauty of modern cam lobes, at least from my perspective.

Food for thought.