Can the CIS airflow sensor/plate be upgraded with MAF?
 

This might be a stupid question and I know there are a lot of strong opinions (bordering on religion?!?!) about the merits/limitations of CIS. My question is very narrowly-focused -

Has anyone successfully replaced the CIS airflow assembly (plate) with another properly-calibrated sensor, such as a more modern MAF, and successfully overcome the "reversion" issue I've heard and read about? I am planning out my next build whch will initially retain the CIS. WOuld such a modification work and if so what kind of effort is involved?

Thanks,
John

If you could wire the the MAF sensor to a processor which controls a solenoid that raises and lowers the fuel distributor plunger, you can get rid of the air plate/meter.

It's more trouble than it's worth, but it would be a fun project. A Megasquirt EFI conversion would be easier.

Souk,
Thanks. For me, going to carbs is the next stop, but I may be forced to keep the original induction setup due to racing class rules. I'm not even sure this modification would be allowed but I am curious if it would work.

Couldn't you simply remove the plate assembly, tap and thread the intake and screw in/epoxy/mount , wire it to a converter chip/resistor or other such electrical device to set the reading range correctly, and wire that into the CIS harness? The point of this would hinge on whether or not the MAF would be better able to deal with the "reversion" feedback better than the plate.

The CIS harness has nothing to do with fuel flow rate. Well, the Lambda circuit on the 80-83 CIS does fine tune the flow rate a bit to get the right exhaust gas reading (O2 sensor feedback to mildly richen or lean the mixture). The circuit controls the frequency valve, but it alone does not control fuel flow. The primary fuel flow is mechanically controlled by the fuel distributor plunger moving up and down as the air meter is moved up and down as air flows through the venturi of the meter.

Although I think it'll be more effort than it's worth, you can proportion the output of the MAF to a solenoid's travel such that fuel rate increases with increase signal output from the MAF, but the air meter is not exactly linear. If you could get a solenoid to react fast enough, you would still need to process the MAF signal to make up for the lack of linearity in the air meter to plunger travel of the normal CIS. You'll need a lot of tuning time if you can get the equipment to perform per spec.

Like I said, it would be a fun project, but I would just go to carbs or EFI.

The MAF would handle reversion better.

Something else that might work, is a damper on the air plate lever arm. But that's a crazy idea too as the damper would prevent free motion of the air plate.

JohnJL. Pat Williams Racing is inthe process of building a CIS to EFI conversion. It retains the manifolds, air filter housing and some other existing parts, and replaces the WUR, AAR, fuel distributorand God knows what other Rube Goldberg contraptions on the existing CIS system. I'm planning to use his kit in my 3.0 build -up. Dan

Why don't you fit an after market EFI to your engine, with a 3.2 inlet manifold and throttle body? The other option is of course is a Triple throttle body set up( rules allowing) There are many options as you would know for EFI systems.
Regards Mike

I really doubt any race class that requires you to retain the CIS is going to allow you to remove the CIS throttle plate and replace it with something else.
-Chris

I amnot sure the MAF would be better on Reversion??? seems like the air going back over the sensor would mess it up..... also the connected intake runners is a problem too because the pulse back up the runner from the one cylinder effects other cylinders. Although Mazda made this work to their advantage on the rotary.

well said, Souk. normally the metering plate is a purely mechanical "sensor", acting on the fuel distributor plunger as Souk said.

The Aussie historic class rules are pretty vague...allows for modifications "within the technology available at the time of manufacture...

Since I'm building for lower-speed (read:twisty) courses and events, perhaps my choice of a lower-overlap cam will negate the reversion issue anyway. Just pokin' around for potential issues.

Maybe this needs another thread, but I'll ask anyway: Given a choice of euro heads (larger intake ports) and US heads, am I better served with the US heads? Faster intake velocities at lower RPMs and the ability to later port out if needed sounds like 2 good reasons to go with the narrower-intake US heads. Sound reasonable? Assume comperable shape and the goal is to build torque quickly at 2000 rpm and up. I'll rarely have the chance to go WOT on a straightaway...

thanks!

Carbs would be legal as "available at the time technology." That is one reason why I'm developing carbs for my car. Yes boys, I'm getting rid of CIS eventually and installing my slide valve carbs! I still love CIS, but for a race car it's obviously not the best.

As for 2000+ torque, that's a pretty tall order. You may be better off to consider gearing, instead engine work, if you will be running the tight courses.

Souk, you are right, gearing is under similar development...