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Calculations

-Actual Speed-

Speedometers can be very inaccurate, but if gear ratios, tire size, and engine rpm (this assumes the tach is correct.......which they are not, mine indicates 5950 rpm at an actual 5800 rpm) are known, speed can be calculated.

For example, lets say I want to know the theoretical top speed of car (if you had enough power and aerodynamics, how fast could you go with stock gearing and rev limiter). My rev limiter is at an actual 5800 rpm, fourth gear has a ratio os .705:1, the final drive is 2.97:1., tire size is 195/70R14, or 815 revs/mile (avaible from here). This is with the toque converter fully locked up however, which never really happens anyway.

5800 rpm / (.705*2.97) * (1 mile/815 rev) * (60 min/1hr) = 203.9276285 mph

-Volumetric Efficiency-

There is a big difference between in the amount of air an engine can move in theory, and what it is moving. It takes some serious tuning on boosted engine to achieve 100%, but it can be done. Here are the calculations I used to find mine @ 5500 rpm. I should of measured lb/hr at peak torque, as that is when volumetric efficiency is the greatest.

-Theoretical CFM = Engine Displacement/2*RPM/conversion factors

(((3136cc/2 * 5500 rpm)/1000000)/.0004719)/60 = 304.58 CFM @ 5500 rpm

-Actual CFM = lb/hr (MAF Reading) * Weight of Air (From a Psychrometric Calculator, Humdity and Intake Air Temp must be known)

16 lb/hr*13.4 (ft^3/lb) = 214.4 CFM @ 5500 rpm

Volumetric Efficiency = Actual/Theoretical

214.4/304.58 = 70.39% @ 5500 rpm

As a side note, while my engine is only capable of pushing around 305 cfm, my muffler (a Dynomax Ultraflo SS) is capable of supporting 999 cfm, according to Dynommax's website. Well, overkill is always good.