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How can we actually measure actual (real) engine air flow cfm

EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals


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How can we actually measure actual (real) engine air flow cfm On a dyno as the lesson states

For our purposes we generally wouldn't measure actual airflow. At a professional or OE level it's possible to equip an engine dyno with an airflow turbine to measure airflow in CFM but this isn't something most of us in the aftermarket industry will ever do. Of course if you have a MAF sensor on your engine this will measure airflow and you can log this in your ECU however it's important to also understand that the MAF sensor calibration relies on the entire intake track to be stock for the reading to be accurate.

I live in a rotary world a 13B in a FD has 40ci per rotor 2x = 80ci at 8500 RPM (there is one intake stroke per eshaft rotation) 3 face per rotor so if I got this right I have 6 face x40ci=240ci per engine period. 240ci x 8500rpm / 1728 = 1180.55 cfm theoretical CFM

So for VE effeciency I cannot calculate the effective % ? I can calculate the theoretical CFM but not my actual consumtion so this is a no go to find ou my actual % VE am I correct or is there a rule of thumb?

Maybe that can help you:

As for how to measure real air flow (actually it's mass flow), that's how it's done:

https://www.youtube.com/watch?v=WQdKVLUdAxo

The rotary engine is a little unique but the same techniques are still applicable. I think the thing you have perhaps missed is that the rotors turn at 1/3 of the eccentric shaft speed so you aren't actually seeing 6 combustion events occur during 360 degrees of engine rotation - This actually takes 1080 degrees or 3 full rotations. If we compare a rotary engine's displacement to a piston engine then it's easiest to compare the two over 720 degrees of crank rotation as this is what a piston engine needs to complete a full engine cycle. The piston engine will displace its engine capacity over this time however in the rotary we would have 4 combustion events occur in 720 degrees of rotation and hence the engine would displace 160 ci or twice it's nominal capacity.

Rotary engines are often discussed as 2 stroke engines as each rotor will have one combustion event per 360 degrees where as each cylinder in a piston engine has a combustion event per 720 degrees rotation.

Does that help clear things up for you?