Camshaft recommendations

Valve timing

A typical standard valve timing is 20°-50° /50°-20°. A typical sport camshaft suited for both manual and automatic gearboxes would be about 25°-65°/70°-20° (270° duration). The "hottest" recommended "street camshaft" is about 290° duration with a timing of about 40°-70°/75°-35°. Many camshafts have so called symmetric valve timing (for example 30°-60°/60°-30°). The outlet valve timing can be advanced about 5-10° with better response at lower revs and more horsepower at middle range.

Valve lift

Standard camshaft lifts about 23% of the valve diameter when racing camshafts can lift up until 35% of the valve diameter. The best airflow happens when the valve lift is about 29-31% of the valve diameter. The gain with more valve lift is that with fast opening and closing but moderate (relatively) duration's and overlap you get a wide torque range without scarifying top end power.

Power range

A four cylinder 2.0 liter engine with 35°-75° valve timing has a power range at about 2500-6500 rpm when a 7.0 liter V8 with the same valve timing pulls from 2000-5500 rpm or a four cylinder 750 cc mc-engine with same timing pulls from 4500-8000 rpm. These figures aren't exact or absolute. The power range varies largely depending on choice of carburettors, valve diameters, porting , OHV-OHC-DOHC and supercharging.

Advancing-retarding

Advancing the camshaft in relation to the crankshaft raises torque at middle range and lower rpm. Retarding lowers the middle range and lower rpm torque but raises the top output somewhat. Retarding isn't recommended in any other case than traction problems due to too much torque at lower rpm. About 2° advancing has a very little effect but 4-8° raises the middle range torque noticeably, the top output is somewhat reduced. For both street & race 6-7° advancing is recommended. With DOHC engines you can play a bit more, you can for example retard the inlet camshaft about 6° thus gaining more horsepower at high rpm and there after advance the outlet camshaft for more torque at lower rpm. It gets even better when you advance the inlet camshaft 4-7° and the outlet camshaft about 6-10°. Note: You should check the clearance between valves and pistons (it should be atleast 0.060", 1.5 mm).

Camshaft dynamics

Most of the Hi-Perf camshafts produce a velocity of 0.007" (0.18 mm) per °, which is generally acceptable. But certain race camshafts has a velocity between 0.009"/°and as high as 0.012"/°(0.3 mm/°). This is higher than most engines limits. The acceleration curb (lifter acceleration) shows how much the valvetrain is able to rotate on a certain time. Negative acceleration sets the maximum rpm. A camshaft that has the least negative acceleration is also able to handle the highest rpm or softer valvesprings. The negative should be lower than 0.0002"/° but 0.00028"/°is acceptable. The positive acceleration shouldn't exceed about 0.0006-0.0007"/°.

Maximum safe camshaft and lifter velocity for ford engines

Camshaft velocity

If TPDD is jumping all around this is most likely due to a manufacturer error, but if the velocity and the acceleration figures shows 4-6 regular errors then this is probably due to polydynecorrection made by the manufacturer to prevent weaknesses in the valvetrain. Polydynecorrection works so that the camshaft acceleration varies so the valvetrain wont be overloaded.

Lifter velocity

The answer is given in thousands of an inch per degree of rotation. If the camshafts velocity exceeds the lifters safe velocity the lifter will accelerate to quickly and rapid lifter & camshaft wear will occur. To prevent this you can use lifters with greater diameter or change to roller lifters witch is the best alternative but also the most expensive alternative.