Converting 964 AFM to 993 MAF

[tholyoak]

So I have had a little too much time on my hands over the winter and have swapped the early aluminum manifolds from my 90 964 engine with later, slightly larger plastic ones from a 993 along with the 993 throttle body.
Now since I already have all the parts I was thinking of swapping out the flapper AFM with the hot film MAF from the 993.

From the factory manuals the external air temp sensor has the same resistance range as the internal one of the AFM so that should be fine, the AFM and MAF both pick up ground and 12V power from the DME and a single wire to the DME for the signal.

Now the question: we know from the service manual that the AFM goes from 250 mV closed to 4.6V fully open, however all I can gather is that the MAF signal goes from 160 mV with no flow to ???

Does anyone know what the upper limit on the MAF voltage is, ie would it be a straight swap as long as the conversion harness is mated up correctly or does it 'sense' a much broader voltage range. Don't worry I would get it on a dyno as soon as converted to verify that the A/F ratios are good just wanted to know if it would even run with the setup or blow the DME with too high of voltage output.

I know there are devices out there that intercept the signal to allow for adding MAF to AFM vehicles but I was wondering if it might be possible to do without these devices.

Todd

[DIANA]

This is imposible.The AFM(VAF)lineal response.The MAF logaritmic response.VAF need IAT for calculation Volumen air.MAF caculation volum direcly.
You need a programed target for transform Maf sensor and your DME understand.
I intend this with "unichip"for my carrera 86,no good result.
I shall want explanation more but the idiom is a problem for me(I´m spanish)
I think that you need a sistem type Authority.I t have a new programation DME for used Maf

Regards

LUIS

[tholyoak]

Luis

Thanks for the response. If you could provide a detailed response in spanish I work with a fellow from Spain and he could translate for me. If this is not a problem email me at holyoak@brandeis.edu

Todd

[ischmitz]

Todd,

Maybe you should pick up an early 993 DME with harness to go with your conversion. I know they are not cheap even used but you could sell you 964 DME / harness to recover some of the costs.

Trying to develop a chip that converts between the linear response and the logaritmic response seems more involved if you ask me. I bet there is some simple conversion stage somewhere in the 993 DME that linearizes the MAF input.

Aren't there barn door to MAF conversion kits for 1-2K$ out there. I wonder how they deal with that issue. Maybe you call up Performance Parts or some other guys that offer those and pump them for some infos. Tell'em you want to know a little more before shelling out the big bucks

Ingo

[tholyoak]

Ingo

The MAF conversions use some sort of black box which while I don't know how it works linearizes the signal as shown here
http://www.pro-flow.com/Product%20pages/vane.htm

Things like the ARC2 are more complex and allow you to 'tune' the signal to optimize the A/F ratio. I guess I was just wondering how the output signal of the MAF compared to that of the barn door sensor and Luis has answered that question.

Looks like your suggestion is the best idea since I already have all the other parts less the 993 DME and harness although maybe I'll see if the adapter at the link above is available separate from the rest of the kit and see how the cost compares.

Todd