While intented to be Turbobuick specific (again Turbo buick, and in
particular vehicles in street trim), it might shed some light on what
other's are doing. For those not familiar with the TBs, they run a MAF system, and the meter pegs are 255gm/sec., which is easy to exceed even with a stock engine. So while you can change the injector constant to accomodate larger injectors, the whole plan still collapeses, since the healthier the motor the faster you peg the meter, and the engine winds up too rich too early. There are some ways around this, but, to date, IMO they seem rather crude. Using the following you wind up with a blend of
Alpha-N and MAF. While not perfect, it does give complete control of the fuel curve, as compared to just hammering the calibration with a pegged MAF.
For those that have taken tuning seriously and have an ecm bench you can fire it up, and if you scanner looks at the commanded AFRs this whole puzzle falls into place instantly. If not then just doing the math, makes it easy to figure out what's actually going on. The difference in the two figures are normally the scanner is looking at a RAM location, and that computation
has the battery voltage correction in it.

Just to shed some light on this I ran some chips on the bench and added some observations.

Given a set of normal operating conditions for temps, and TPS values. Using an injector size of 55PPH, and a MAF of 160 to acheive a commanded AFR of 12.5:1

At 3K RPM, the DC is 63% and at 5K 62.6%

Now to repeat that with a MAF of 255 we get

At 3K, 98.4%, and at 5K 100.1%

So what does that really mean?.
If you want to peg the meter, fine, but when you peg it you've just about totally wiped out getting any resolution, with the 255 entries there is just nothing left. You can't change a darned thing.

HOWEVER,
Look at what happens when you limit the MAF reporting to 160. You still have PW to play with. Lots of time to add PE vs TPS, or RPM.
If you want to run on a pegged MAF that is a valid option, but your hands are tied for what you can do.

to continue........

Since we're at 24 PSI +-, those 55s are more like 70s, since the FP increase as function of boost.
So we'll run the MAF at 160, and we get
At 3K 49.7% DC, and at 5K 49.4%

Now the run the 255 value, and we get
At 3k 78.5%, and at 5K, 77.9%


So now whatdawedo?.
Let's see we know what DC give what AFRs, for a Given injector. We know when our boost begins, we know the injector's new flow at max boost, and the DCs we need to get a desired AFR, so we just need to figure out if we want to add the fuel via RPM or TPS. Yes, there are other options, in how to handle this, but my suggestion is this way.

But, it still takes a Translator to get around the oem electronics.

And this was just about Table #5, and there are 4 others to worry about.

Not to be attempted without adult supervision, for off-road use only, educational purposes only, feet on the floor and don't hit Billie.

 

Has anyone ever built a flow bench for MAF sensors? You inject "known" flow amounts (either GMS or CFM) and measure the outputs from the MAF in volts. I think this kind of setup would really give a leg up in learning how and when to mod the MAF tables in the prom. I would think it would also give insight into why the MAF tables are they way they are.

 

IT would be a good tool (and one that Grumpy has been telling MAF guys to build for a long time now) but it would only measure one thing and leave out other parts of the equation. It ends up being like a cylinder head flow bench. They run the valves always open but what kinda engine runs with the valve always open? Same with the MAF in a running engine, the air through isn't a beautiful constant stream at all flow points.