Why is it...
I noticed that too, but if you know your Mopar cam providers, the lift will often be like a signature.
For example; who all makes a .509 cam? and how many different durations go with that?
If you tell me you have a .509 cam in your engine, I'm going straight to the Mopar catalog to find that it is a 292/292.. This may be a poor example, cuz everybody recognizes the 292/.509 signature. But you get the idea.
Wouldn't two cams with equal duration and LSA share the same rpm range even if their lift was different?
If equal duration at .050 and same basic type ( like FTH) then possibly/probably yes. But you cannot directly compare different types of cams, because the lobe-shapes are different.
Furthermore, two different manufacturers might have identical durations at .050; but by .200 lift, one of them could be out in front, maybe up to a cam-size bigger. This will change the rpm range.
Advertised numbers are a crapshoot, because the manufacture of any cam can pick and choose the starting and end-points to arrive at whatever numbers he wants; there is no standardized lift specification. One manufacture might choose .006 tappet-rise; while another might choose .008, and another , .001. Those cams could all be the exact same cam, but will have three different advertised numbers. Furthermore; what happens between advertised and .050, from the specs, nobody knows. The ramps could be long, short, or in between; which will not affect the power or rpm range, but it could affect the idle..... a lot; like a Whiplash or a Thumpr.
