HKS Super AFR

[cat007]

Hey all,

I have asked around various forums but have yet to get a confirmed reply.

I have a 1G-GTE (2litre) supra which uses the flapper door style AFM.

I have recently purchased an HKS Super AFR, however on the HKS site it states:

"The Super AFR is compatible with virtually any fuel-injected 2-12 cylinder vehicle that uses a hot wire, Karmann Vortex airflow meter or pressure sensor."

It doesn't mention anything about the flapper door style AFM however on various other sites such as www.titanmotorsports.com and www.turboimport.com they say that it works with most MAF, Speed-density, Flapper door, and carmen vortex metering systems.

Can anyone please confirm that it WILL work on a flapper door style AFM and what should the dip switches on the back be set to?

Thanks

Hunt

[Jeeves]

I wouldn't hold your breath, I think they're just using that as a generic statement. Let's take a look through the HKS Documentation:

[img]http://www.**********s.com/pics/SAFRinstall.gif[/img]



[img]http://www.**********s.com/pics/SAFRwiring.gif[/img]

I'd place my bets it was never designed to work with a flapper door system. HOWEVER, It all depends on what that sensor sends out. That's how the AFR will modify the signal. So if the flapper door scales in 0-5v, I'd say hook it up for the 0-5v signal expected from a Hot Wire system and set the dip switches as such.

HOWEVER, it does NOT list the Flapper Door style AFM as compatible. So, the scaling could still be off. IMHO, your best bet is to research other cars that have flapper doors, and see how others have those dip switches.

Looking on an MR2 forum, it seems people have tried and not gotten it to work with the Flapper Door. Here.

Just a quick rundown of the types of AFM's:

Hot Wire: a skinny wire inside the air tube; it needs a control module too. The control module measures the amount of electrical current required to hold the wire at some fairly high temp... this current can be used to figure out how much "cooling" the airflow is providing... couple this with measurements of ambient air temp and ambient pressure and you can get airflow. The output of such a sensor is non-linear; i.e. if you double the airflow you do NOT get twice the signal... it's probably more quadratic which means you'd get either the square root of two or four times instead of twice the signal. Your engine ECU has to "know" this and compensate for it. Also, the controller, every so often, must over-current the wire to "burn off" junk that sticks to it. So your ECU must know when/how often to do this AND how to continue computing the fuel needs of the engine while the sensor is cleaning itself.

Karmen Vortex: (7M-GTE Mk3 Supras) Ever stick your finger in a quickly rushing stream or other water flow? Remember the circular eddies that formed downstream - in the wake of your finger? That's Karmen vortex in a nutshell. If you look inside the metal AFM container of the 7M-GTE's mass air sensor, you'll see a plastic bar bisecting the opening. This bar is wedge shaped... air flows smoothly over the point of the wedge but the abrubt flat trailing edge leaves a big wake. The air makes eddies/vortices trying to fill in this area. Just past the wedge, on either side of the sensor assembly, there are two small round electrical things. These are ultrasonic transmitter/receiver units, just like a motion detector burglar alarm. When an eddy/vortex passes between these two things the signal changes a little... and the electronics in the square box on the sensor amplify these changes converting them into a digital pulse train. The higher the pulse frequency the more airflow is going through the sensor. A unique property of a Karmen Vortex sensor is that it's LINEAR with airflow. You still need ambient air temp and pressure signals along with the frequency output to know the actual airflow.

Pressure sensor: generally a small strain guage which is just a skinny resistance wire wound in a zig-zag pattern on a flexible surface, pressure flexes the surface and thus the wire too causing a small resistance change. Others are solid state (i.e. like transistors) and use the pressure to flex an electrical part that then changes resistance, capacitance, or even inductance depending on the type of sensor. Some are linear output, others are very non-linear - such as quadratic or logarithmic.

Flapper Door: Another common type (used by early Bosch EFI systems and many Toyotas) is a spring loaded flapper door. This door literally blocks the intake air hose; airflow pushes against the door (compressing the spring) so the more airflow you have the more the door opens. A potentiometer or other electronic gizmo measures the movement of the flapper door. These are typically large sensor assemblies and often have cases that look like pie wedges - 1/4 of the pie. Usually you'll see two pie wedges: one in the airflow and the other off to the side. The second one is a damper and compensator/balancer assembly. These things are very non-linear; in fact they are quadratic. Twice the airflow pushes the flapper door roughly four times as far open.