MoTeC Global Forum

Hello,

We are running a na 600cc Formula SAE engine with M880. We use TPS for efficiency calculation with MAP compensation. The question is should we also run a barometric pressure compensation? Another issue is the restrictor that causes the MAP reading to fall at high rpms when the restrictor chokes. Should we just turn off the MAP compensation at high rpms?

TimoK:>Should we just turn off the MAP compensation at high rpms?

If manifold pressure falls at high RPM, wouldn't this be a good indicator of the potential airflow (and fuel need) through the engine?

TimoK:>should we also run a barometric pressure compensation?

Once your intake chokes, what is Baro telling you?

Typically you would use MAP or BARO, not both.

It sounds as though your original setup is in the ballpark. If you are looking for improvements in your EFI control strategy, you are likely to find them in transient conditions due to the long length of the typical FSAE intake system.

Eric Schieb
Electron Speed

Timok

Map compensation is a good thing especially in restrictor class racing.

As you have seen. Once the flow of air attains sonic velocity (critical velocity in fluid mechanics) through the restrictor, The engine goes into choke and as such, you should see a related drop in MAP (below 100kpa). This is a good thing because now you can adjust BOTH timing and ignition based on this measured "VE" since the "VE" is closely related to kpa reading. Keep in mind that you really do need the MAP readings even in choke as you do not know what the choke curve is until the motor is run and as such you need to take fuel away based on that map reading and also adjust ignition timing for the lack of fuel & air.

Now the baro compensation can be used as the exhaust velocity will change and that affects overall VE. Of course if the course is fairly flat than the "baro" comp will really not be needed much. Now if there are a lot of elevation changes than you will benefit from the "baro" compensation (which really is exhaust gas velocity comp ).