Reply to "393C Stroker Recommended Cam"

Five hundred horsepower is a lot of "street-able" horsepower for this 40 year old engine to produce. It’s easy to build a 440 horsepower Cleveland street engine. But 500 BHP was an expensive, rough idling, pro-level racing engine 40 years ago. In fact De Tomaso raced Cleveland powered Panteras in the World Endurance Racing series with only 440 horsepower; they kept the horsepower down at that level in order to achieve reliability with the production castings. I’m relating this to you for a reason.

Without all the right components and engine prep I advise people to limit engine speed to 6200 rpm. That’s 3600 FPM mean piston speed with a 3.50 stroke. But with a 3.85 stroke 3600 FPM mean piston speed is only 5600 rpm. However with the proper components and prep you can set the rev limit at 6600 rpm (about 4200 FPM mean piston speed). That's a gain of an extra 1000 rpm. 4200 FPM is all the piston speed the production block was designed to endure. The popularity of "stroker" engines today was not a consideration when the engine was designed in 1967.

A 500 horsepower Cleveland is still an expensive engine to build if you expect it to be durable. Perhaps the biggest concern is the production engine block's thin cylinder walls; your stroker kit has a rod length to stroke ratio that's a little less than the limit I would advise (actually a 3.85 stroker kit pushes all the limits a little too far). The slipper skirt style SRP pistons are not the best choice considering the thin cylinder wall issue, round skirt pistons would be better. Unfortunately no stroker kit manufacturer supplies round skirt pistons with their kit.

My camshafts have an amount of overlap and an IVO which promote good drivability and vacuum. Engine performance from idle to 3000 rpm is prioritized higher than performance above 4000 rpm. I design to achieve wide flat torque curves, which are ideal for street engines, circuit racing, autocross, winding mountain roads and stop and go city traffic. This is not the type of curve however that drag racers prefer, nor is it the best curve for reaching a high peak number on a dyno. I also emphasize durability, longevity, and reliability. All these things are key attributes of a street engine. Here’s the camshaft, it’s a custom ground camshaft. It’s the biggest camshaft that can be called a “street cam”; in other words it runs up against all the limits I place on street cam design. The valve lift comes close to the 0.630” maximum lift limit of the Manley valve spring I recommend.

Bullet Cams
Intake Lobe = HR285/360
Exhaust Lobe = HR291/360B
LSA = 114°
Index camshaft +1° (advanced)
Intake lobe mathematic CL = 113°
Exhaust lobe mathematic CL = 115°

Duration at 0.006 = 285°/291°
Duration at 0.050 = 231°/236°
Gross lift = 0.623/0.623 (1.73 rocker arm ratio)
Overlap = 60°

Valve events based upon duration at 0.006
EVO = 80.5°
IVO = 29.5°
EVC = 30.5°
IVC = 75.5°

Since the intake valve closes at 75.5° ABDC do what is necessary to nudge the static compression ratio up to 10.5:1 in order to achieve 7.6:1 dynamic compression. That's premium pump gas friendly (91 octane US/Canadian pump gas or 95 octane pump gas everywhere else in the world). Any more compression or higher octane fuel puts you into cylinder wall cracking territory ... avoiding conditions that lead to cylinder wall cracking will be important if the engine will actually see 25% track use because cylinder walls crack at wide open throttle, when volumetric efficiency & therefore cylinder pressure is highest.

For induction and exhaust consider the Blue Thunder intake manifold, with the exhaust heat passage welded closed (but do not lower the plenum divider); 850 CFM carb with annular boosters; and low back pressure exhaust & mufflers.