jimbo1111

John lets not get to crazy here. What I'm saying is that it doesn't matter weather I send a maf signal or a afm signal to the dme. The difference is you add the conversion factor into the chip. My conversion factor is in the PB. The conversion factor is linear.They both cancel each other out.
The main difference is the chip maps. You have to scue the correct map on the chip so you don't affect timing. You do that by having the correct value for fuel in place. When the engine is loaded it will scue the correct timing for the load/voltage that the dme see's. Both systems will work identical. assuming I had a afm chip that was tuned with 55 lb injectors.

TT

It is not a conversion factor as in voltage to voltage conversion. The transfer function in the DME calculates the air flow based on air meter input voltage. If you just did a MAF voltage to VAF voltage conversion then it wouldn't matter if you used a piggyback or did it in the chip.

I've put more different model MAFs on my 944 than I can remember. All using the stock fuel maps. The only thing that is changed is the air flow calculation based on input voltage in the chip. Do it outside the chip and you are limited to the stock VAF calculation.

jimbo1111

It's the same calculation. The maf output voltage is very similar to afm's. It really makes no difference whether that calculation is before the dme or on the chip. The point is that you can tune a afm signal identical to a maf signal. If the dme see's a 1.2 volt signal from a maf at 200 cfm an afm signal will have a 1.1 volt signal at the same cfm. So I would plot a injector duty cycle at 1.1 volt on the lookup and you would plot it at 1.2 with the same timing. There is no differents.

fast951

Jimbo, what you are saying indicates that the MAF you are using is very close to to the VAF in flow... So what's your pointe?

Read back prior posts, not all MAFs have the same curve..

TurboTommy

I've been reading this thread; I could be wrong, but it almost seems like there are two different issues here that shouldn't even be intermingled.

An air flow measuring device, whatever it is (AFM, MAP, or MAF) gets maxed out from some pre-determined amount of AIR FLOW, and does not care of you change injector sizes all over the place.
According to the orginal question, why would the AFM or the MAF even be addressed?

Jimbo,
I think you have some root misunderstanding about injectors and their marriage to engine demands.
I did once as well, and then one day it "clicked"
Everybody gave you the right answer to your question.

jimbo1111

The point is that I don't need a maf specific chip. Nobody does. What I need is a well scaled chip for fueling with 55lb injectors.

TT

I don't know where you get that idea, it is not the same calculation. The MAFs I've used read less than half the voltage at idle than the VAF would put out for the same air flow. The difference from there on up from idle to WOT varies and you might get one point where the voltage curves cross for the same air flow. I've used MAFs that read no more than 3.5V at WOT while the VAF would have been well over 5V for the same air flow.

With a chip, f(v) = flow (Kg/Hr or SCFM, take your pick). For v = 0..5V f(v) MAF != f(v) VAF except maybe at one point, it depends on the shape of the MAF curve. If you use a piggyback to make f(v) MAF == f(v) VAF, then you are OK, but you are limited to the maximum flow value calculated by f(v) VAF where v = 5V.

If the MAF you are using is capable of measuring more air flow than the VAF [f(v) MAF > f(v) VAF where v = 5V] then your piggyback is limited to that flow with f(v) VAF and v = 5V. For example if f(v) VAF = 600 SCFM when v = 5V and your MAF reads f(v) MAF = 600 SCFM when v = 3.5V, then the piggyback is limited to output a 5V signal when the MAF input >= 3.5V. You are limited at this point. Putting the f(v) air flow calculation inside the chip removes this limit. A updated function can calculate air flow for this example at voltages >= 3.5V.

Again to just reiterate, you CAN use a piggyback to make a MAF signal look just like the VAF signal. BUT you will be limited to the maximum airflow that the stock VAF calculation inside the chip computes at 5V input. There is a difference once you exceed that maximum stock computation. You will more likely hit the load limit along with OBP before you reach the 5V maximum VAF input. Good luck.

TurboTommy

There are still two separate issues going on here.
The MAF specific chip issue is how well the Maf---Chip---DME combo work.
The chip vs injector size is something entirely different.

So, yes, Jimbo whenever you go up in injector size you need to decrease the pulse width, which is usually done via the chip.

jimbo1111

TT I think you have it wrong. Most maf regardless of size put out 0 to 5 v. Some reach 5 volts at 500 cfm others reach it at 700 and so on. A 75mm maf will put out 3 volts at say 300 cfm and a 85mm will put out 2.5 volts at the same cfm. When the piggy back transfers 5 volt signal from a maf to a afm signal its done a calculation witch will be close to 5 volts. At 5 v an afm is putting out 300 cfm, a 75mm maf at 5 v is putting out 600 cfm. A 85mm is putting out 800 cfm The transfer is still very close the only thing that changes is the cfm flowed by each. The differents is that the the motor is ingesting 500 cfm rather than say 300 that a stock system would see. Now throwing in injectors will solve your top end needs but you have to start to massage back the signal in the low rpms because before boost hits you still have a stock engine with stock engine needs. Now you have a problem with to much fuel down low. The way to fix this is to scale back the chips when off boost and part throttle. You can do this in the chips so the timing maps are still where they have to be.

macnewma

Just a quick question concerning MAF to AFM transfer functions:

If a MAF were calibrated to emulate the exact f(v) = flow of the stock AFM, could you use AFM chips and not worry about a thing? The disadvantage to this would be that the maximum measurable flow of the MAF would be limited to the maximum measurable flow of the stock AFM, right?

Thanks,
Max

fast951

Yeh TT, you got it wrong. We all do...

macnewma

Come on John, I am not trying to say you have it wrong at all. I completely understand your approach and I believe it is a superior approach to the MAF setup.

I am just curious if what I said is still valid although not the best solution.

Oh and as a disclaimer, I don't know jack about Motronic or fuel injection.

Max

Tomas L

Correct.
A problem aside from the transfer function that you will get when you use a MAF with AFM chips is the temperature density correction that the AFM needs but a MAF doesn't.

Tomas

macnewma

Thanks Tomas.

Is that what the IAT sensor that usually accompanies this type of MAF setup is used for?

Max

fast951

My response was not to you, you posted while I was typing . My message was triggered by Jimbo's message "TT I think you have it wrong."