If you put a cam in an engine and it has some impresisve specs RE: lift, but it runs like a crippled turkey, it's probably not the lift that's causing the problem.
I think that to get meaningful cylinder pressure at the rpm's you want and need it, you have to take into consideration the size of the engine, its design parameters (long-stroke, small bore vs. short stroke, big bore), its compression ratio (long duration cams need more compression than short duration cams), and overlap (the amount of crankshaft rotation that occurs while both valves are open.) Lobe separation angle (lsa) is another consideration that can change a cam's "personality," but it's not as big a factor as lift and duration.
The amount of valve lift a cam produces won't always dictate what kind of a cam "personality" is exhibited in real-world driving. I have a cam in my Valiant that is extremely mild compared with most accepted statistics for "performance" cams; it only has 214 degrees duration at .050"-lift on the intake side, and 218 degrees on the exhaust, at .050". That's practically a stock cam for a 360 truck motor, BUT, it has very aggressive lift ramps (roller), and has a whopping .525" of lift, at the valve. So, what we have here is a high-lift, short-duration cam that idles at 475 rpm with good vacuum, but pulls strongly all the way to 5,500 rpm, due to its agressive lift ramps and (relatively) high total lift.
So, in this case, lots of lift doesn't always mean soggy performance at low rpm.
If you put a long duration cam (say, anything over about 230 degrees at .050"-lift) in a 318, for instance, it would not run well, probably, unless you had 10:1 compression, or more. The problem is exacerbated when the engine is small; you can get away with a lot more cam in a 440 than you can in a 318, compression ratio being equal.
Next time you have a chance, check the cam card for duration specs on the cams you've been running. More lift doesn't necessarily mean more duration, and vice/versa. In fact, they're not really related, at all.
Lobe separation, as I understand it, works to make more power at higher rpm's with lower lobe separation angle numbers. That is, a cam with a 104-degree lobe separation will make better high rpm power than one with a 114-degree "lsa." Overlap is minimized with higher lsa numbers, and increased with smaler lsa numbers. An engine's idle that was rough with a 104 lsa cam, might smooth out considerably with the same cam specs, but has a 114-degree lsa.
I don't pretend to know anything about cam design; those are just a few facts I've picked up through magazine articles and personal experience.
If anyone has good info to the contrary, RE: what I've said here, please correct me. But, choosing a cam, thinking it will perform differently insofar as its "personality" because of its lift, alone, isn't the best way, I would think.
Just my two-cents....
Bill
