Yeah I know it's not going to actually simulate true engine conditions. But if the port flows say 200 cfm at .300 lift with 28" of test pressure and say 300 cfm at .500 lift with 28" test pressure then it doesn't tell us anything about what engine speed that 28" of pressure will occur for both lifts.By the time 28" is reached at .300 lift then what will the pressure be at .500 lift during the same stroke?You're right there is too many differentials to generalize.I'm only guessing that by not changing the test pressure on the bench and using the same number of vacuum motors with the air valve opened at the same point....it would more closely represent the true vacuum at the same engine speed for both lifts.Thanks for the input.