Forced induction and MAF sensor
Moderator: martauto
No. MAF (mass air flow) sensors are in fact well suited to forced induction given that they fundamentally respond to the mass of air that flows over the sensor element, and it is indeed a measure of the mass flow rate that is required to determine the measure of fuel that must be injected into the engine.cee wrote:Am I right in believing the two cannot mix?
Specific problems related to the use of MAF sensors on FI engines inlcude the output of the MAF sensor clipping due to the fact that it was only designed to measure say X amount of air on a normally aspirated engine, and now it is expected to measure X+Y after a turbocharger or supercharger has been fitted. This simply means that a MAF with a wider range is required, and it is not a fundamental failing of MAF sensors in general.
When using a MAF sensor on an FI engine one must, however, pay attention to the correct use of a bypass or blow-off valve. Both must be of the recirculating type else the sensor may account for air that ultimately does not enter the engine.
HTH
Geoff
"It is amazing how many drivers, even at the Formula-1 level, think that brakes are for slowing the car down." - Mario Andretti
Put that way - yes of course, makes perfect sense (I'm evidentally being a bit dim...) So you're saying that all that is needed is an uprated sensor? Is this the same for both vane and flap types?
1990 Sterlingsilber 318iS - 146 bhp / 192 Nm
cee wrote:this the same for both vane and flap types?
MAF sensors include hot-wire and inductive types (speaking generally, not specific to BMW)
Vane and flap type sensors are AFMs (air flow meters), not MAFs
The flap type measures volumetric flow only and the vane type somewhere between mass and volumetric flow (iirc).I guess, technically, that MAF's are a subset or type of AFM, but I tend to think of them as separate devices. It is quite possible to use flap or vane type AFM's on a FI engine (The R5Turbo used a Bosch K-jetronic system, for example, that used a flap type device to press against a fuel distributor). They are not ideal though. To bring them up to standard the output of a vane or flap type AFM should be temperature compensated in order to convert volumetric air flow to mass air flow.
If you are thinking of building an FI engine an inductive or hot-wire MAF sensor off a GM vehicle would be a better idea. These days, however, a speed-density system that uses a MAP sensor is easier and more popular.
Last edited by GeoffBob on Fri Oct 15, 2010 1:31 pm, edited 2 times in total.
"It is amazing how many drivers, even at the Formula-1 level, think that brakes are for slowing the car down." - Mario Andretti