RKD in OKC

If you are replacing an AFM with a MAF, it needs to be calibrated to send the same voltage range to the DME as the AFM no matter how much more air you are sucking through it. If the max voltage is too low then the DME does not see a load condition and DOES NOT advance timing.

fast951

True If you are using a MAF sensor with AFM chip/software. This is the "incorrect" way of doing things. Signal must be adjusted with higher boost, change in temps affects it, and timing at PT will be off.

The proper way to use a MAF is to recode the software and use the correct transfer function for the MAF in use. Not all MAF sensors are calibrated the same, so a transfer function is unique for the MAF in use.

RKD in OKC

And if you don't have a chip burner to reburn chips every time you want to change boost levels, or add or substract a performance enhancement you can use a piggyback to match or calibrate the MAF output to the unique transfer function in the chips you already have.

fast951

That's one way of looking at it, however if the proper MAF sensor and proper software was used from the beginning you wouldn't worry about retuning!
(proper MAF sensor means it will handle more flow than the engine can possibly flow even at very high boost. Proper software means correct transfer function for the MAF in use).

With the correct approach (correct MAF & software), it does not matter if you run 12psi or 24psi, the DME will ALWAYS know the "correct" flow and will handle it for both timing and fuel.

No 2 cars are 100% identical, there are variation in spoolup characteristics etc.. The PiggyBack is used for fine tuning to match the car in use 100%. PiggyBack should not be used for "drastically altering the MAF signal to get proper AFR". Even though many people use the signal massaging, I believe it's the incorrect approach. But then again, as you said, very few people know how to write software for the 951.

Rogue_Ant

So how much does increasing to 55lb injectors w/ only a piggyback (no chip) increase PT timing? Is it extreme enough to worry about engine failure?


Rogue

Rogue_Ant

Anyone?


Rogue

RKD in OKC

When I was tuning and running 55# injectors to get the correct AFR I was only sending about 4.1 maximum voltage to the DME and was not getting any timing advance PT or WOT.

Rogue_Ant

Ok, how do you know that? I'm just trying to understand. If your reporting a lower voltage in order to get a correct AFR, you telling the ecu that there is less load. BUT if it didn't have any effects on timing, then that would mean that IGN timing isn't load based...


Rogue

hally

I've put up some of the data on the MAF chip i've developed to run with the lindsey maf sensor, has some info on transfer functions which may be of interest.
With respect to part throttle timing, anywhere on the curve where sensor calibration doesn't match the transfer function, you will look up an incorrect timing location in the PT table posted previously. You can see that PT timing varies a lot against load & is pretty fine grained (12 timing values per RPM column)
Its not easy to describe an alternative transfer function to stock within the limitations of the configurable transfer function tables on the DME. There's a curve that is repeated in each segment, and ideally you want that curve to vary in shape in different segments of the function, so its a compromise. I think Vitesse might have overcome this by moving the transfer function off chip onto their plugin board where they would have the memory to decribe it more flexibly & fine grained.
http://gregorh.customer.netspace.net.../mafchips.html

hally

My FQS scaling factor for delphi 55# injectors is 26% smaller than that for stock injectors (both at 3 bar fuel pressure). Have a look at the PT timing map i posted and you can see approx where that would shift you to.
Another issue is that load is one of the triggers used by the DME to switch from the PT to full throttle map, so you would end up staying on the PT fuel and timing maps longer.

toddk911

So the DME was getting a false reading and then adding timing and/or running rich?

RKD in OKC

With the 55# injectors and 4.3 volt tune to the DME for correct AFR it was running OK, but the power did not have any omph from 4000 rpm up. When I switched to 48# injectors I was able to tune the Voltage from the MAF to 4.6 volts max with good AFRs. It made a 15 to 20 hp difference in a dyno run. The AFRs were the same on both runs. With the correct maximum voltage to the DME, the DME advanced timing. With the lower max voltage the DME did not advance timing.

toddk911

Ohhh ok. Got it now.

I still need to follow your email advice about checking my votltage from the MAF.

When I do and if it is not the full or close to 4.7, how do you fix that?

RKD in OKC

Turn the fuel pressure down and up the MAF output. The problem I had with my 55# injectors is that I had to turn the fuel pressure down to 20# to get the MAF voltage up to 4.6. I am running a Super61 turbo and for that powerband 48# injectors work great. At 16 psi of boost I am running 40# fuel pressure static.

toddk911

How do you adjust the MAF output?