When someone refers to lift, they could be talking about 2 different things.
Valve Lift
When talking about camshafts and lift, people usually mean valve lift. This is the distance the valve actually moves. It is also called "gross lift." All camshaft manufacturers list this value.
Cam Lift
This is the distance the cam lobe rises away from the base circle of the camshaft. It is the distance the lifter will move. It is also called "lobe lift." Some camshaft manufacturers list this value.
How is it measured?
Lift can be measured using a Dial Indicator. You will need to know the Rocker Arm Ratio to calculate. On most engines, valve lift will be greater than the lobe lift.
The formulas are as follows:
Valve Lift = Lobe Lift x Rocker Arm Ratio
Lobe Lift = Valve Lift / Rocker Arm Ratio
Example #1: A camshaft with 0.270 in. of lobe lift will have 0.432 in. of valve lift with a 1.6 rocker ratio.
Valve Lift = 0.270 x 1.6 = 0.432 in.
Example #2: A camshaft with 0.468 in. of valve lift with a 1.5 rocker ratio has 0.312 in. of lobe lift.
Lobe Lift = 0.468 / 1.5 = 0.312 in.
Measuring Lift with Solid Lifters
When calculating valve lift for a cam with Solid Lifters, it is important to account for Valve Lash.
Example #3: A camshaft with solid lifters, listed at 0.630 in. of valve lift and adjusted to 0.015 in. of lash, will only move the valve 0.615 in.
0.630 - 0.015 = 0.615 in.
How does it affect performance?
Increasing valve lift allows more open space in the intake and exhaust ports of the cylinder. Theoretically, this means more air and fuel can be drawn in. More exhaust gases can be pushed out.
Are there other factors to consider?
- Clearance Issues: If the valve is pushed open too far, it can hit the top of the piston. This could cause significant damage.
- Cam Lobe Profile: To increase the height of the cam lobe, it must either be wider or have a steeper ramp.
- A wider lobe increases Duration. This has its own effects on performance.
- A steeper ramp is desirable because it opens and closes the valve faster. However, too steep and the edge of the lifter can dig into the lobe.
- Follow this link for more on Cam Lobe Profiles.
- Additional Upgrades Needed: To take full advantage of increased valve lift, the following systems should be upgraded:
- Air and fuel delivery system
- Ignition system
- Exhaust system