This is the conversion from the "low cam" 8-bit RPM values used for VTEC crossover points and in the low-cam tables. It involves some modular arithmetic, so it's easier to break it up into a couple extra steps. # Y = input value, 0 to 256 # let H = floor(Y/64) ''Where floor(x) = trunc(x) = int(x) = integer part of x. Fractional part truncated. Whatever you want to call it'' # let L = Y - (H-1)64 # RPM = 1875000 * L * 2^H / 240000 You can also do it this way, using the modulo operator: # Y = input value, 0 to 256 # Q = Y div 64 ''(integer division, same as floor(Y/64) above)'' # R = Y mod 64 ''(modulus, i.e. remainder after division)'' # RPM = (2^Q)(floor(R*500/64) + 500) This turns out to be a piecewise linear scale:

• 00h-40h = 500-1000 RPM
• 40h-80h = 1000-2000 RPM
• 80h-C0h = 2000-4000 RPM
• C0h-100h = 4000-8000 RPM

EDITED COMMENT: <---- Linear scale??? yeah right!...this formula need to go back to the "drawing board". The values below shows a perfect exponential scale! I have trying this equation and it does not get exact values. Ben's equation on BRE are more accurate at least on test values...( I don't know the formula for BRE)) That's ''piecewise''-linear. Four linear ranges. It's not a smooth exponential curve. The first formula fairly closely follows the OBD1 code, while the second is a simplification which gets slightly different results with integer math. By what measure do you consider which is more accurate? See https://web.archive.org/web/http://pgmfi.org/phorum/read.php?f=13&i=3314&t=2968 for reference. --AndySloane