Jussi

It seems that stock 993TT MAF is rated about 550hp..
Has anyone replaced that housing (90mm?) with bigger one, like 100mm diameter?
That should extend level from 550 to 680 hp..

Or are there any good aftermarket 100mm MAFs which could be used in 993TT? How about voltages etc..

And yes, that new one can and should be reprogrammed with new transfer functions
and no, I don't want to convert my MAF system to MAP

viperbob

Protomotive uses a resistor network to cut the voltage signal down about 25-30% going to the ECU. Obviously then the ECU is mapped accordingly to the new signal recognizing true airflow.

So you are limited in the HP from an electronic perspective (ECU does not like to see certain values outside of its' hard set perameters) rather than a airflow limitation.

Acropora

The MAF supposedly flows enough for 650hp then is done.

Jussi

That's very high rating..
I have only heard about 550 and 580 hp max.levels from realiable sources.

Max. voltage is 5.0 V, or isn't it?

viperbob

Not true... I have a number of guys running 540-560HP (yeah multiple dynos locations etc) with Kevins Stage 2 turbos and the MAF. K24 Hybrids are then WAYYYYY above this level.

Jussi

Are those K24 Hybrids still using MAF based ECU tuning?
Could someone, with these highly tuned 993TT, check voltage readings when acceleration hard(full throttle) on 4th or 5th gear?
Voltage meter should be connect to MAF wires pin 2 (HFM signal) and pin 4 (HFM ground).
I would be very thankful from these informations!
My 993TT's MAF exceed its 5v level already in 4200-4500 rpms depends on gears..

TB993tt

Forget the dynos, show us some 60-130s

If they are full weight 4WD 993tts then we have the data: 9s gives you about 500 Porsche hp (Bill S -490hp Ruf).

People have short memories on here (VB ) -I spent a pretty penny proving that massive stage 3 K16 turbos could only give ~500 Porsche hp on a fully built engine.
K24s and MAF network will only go above 550 Porsche hp with 3.8 and special parts and then the limit will be sub 600hp.
(note: "Porsche hp" means a power curve similar shape to stock Porsche on a loaded engine dyno with 80/90% of peak power from 4500rpm to 6000rpm, this is what delivers the acceleration numbers)

This is only up for debate if you can show us a genuine 60-130 with all data (weight, climate conditions 4WD/2WD) declared - if not it is just out of date talk IMO.

Jussi

Yes, I totally agree with TB993TT
Many super hyper power packets claim massive HP readings but real measurement on the road tells the truth.

When I tried these acceleration tests on the road, my stock MAF can't measure over 400 g/s air flows. MAF exceeds 5 volts already in about 4200-4500 rpm and power reading there is something about 520hp with 18% transmission lost corrected (awd connected).
If someone else could measure voltage readings from their high power MAF based 993TT, I would be appreciative from results

I have to build some resistor network system to lower these voltages down to 5V at 7000 rpm and then remap MAF ECU tables..
Should I put resistor divider to output 0-5v or input 12v lines?

Jean

js, you answered your question.

If the stock MAF measures maximum 400g/s, which is around 52lbs/minute, and your (993TT) engine flows about 8.5-9.0HP/lbs of air/min. That puts the limit of your stock MAF anywhere between 440-460Hp. If you want more, you need to upgrade it or modify it.

You can use larger MAF sensors from Ford or other car brands that can take you up to 800HP maybe if you wish, but the problem lies in the tuning of a MAF fitted engine, it will not work, that's why experience has shown that beyond the numbers that TB is giving, MAF tuning is gone. See below a post I did on the 996TT forum. Info based on my tuner's feedback

Jussi

I checked that thread also, very interesting reading, thanks!
and funny that it came up almost while than my problem solving.

After speaking with my Motronic tuner, I am wiser again and I'll choose another way to solve my problem..
as you said, those bigger housing or different brand MAFs are very difficult to determine to use proper mappings in all boost(/load) areas by reason of complexity of MAF measurement element and electronics - they are not linear systems..

It is much simple to keep that stock MAF and only limit over 5v error readings to exact 5.0v. for example like putting 5v zener diode to stabilize max rating.
Because when driving over 4500 rpms it is always case that you have full throttle and engine can use full throttle mapping(TPS) with correspond rpm readings and so adjust correct fuel supply etc..

fast951

I'm not a regular on this forum, however I do have a bit of experience with MAFs and DMEs.

There are various types of MAF sensors. The signal poutput can be 0-5Vdc, 2.5-7+Vdc, or a frequency based MAF. For now we will just work with the 0-5Vdc MAF.

Each MAF sensor has a "calibration curve", basically it's a curve describing the relationship of the signal (0-5Vdc) to the Air Flow.

It's possible to have two MAF sensors that look identical, but have different calibration curves. In general, a higher curve will generate a lower signal for the same air flow. The same a lower curve will generate a higher voltage for the same air flow. If a MAF is maxing out (+5Vdc) at lower RPM, can be converted to a higher curve to measure further up the RPM. The shape of the curves may be shifted UP or DOWN (the whole curve, not just a portion of the curve).


The DME must know how to translate the 0-5Vdc MAF signal back to air flow so it can determine the load, fuel and ign. The "transfer function" is where the DME converts the MAF signal.

If you change the MAF curve without changing the transfer function, the DME will calculate the incorrect data (Rich or Lean, Ignition will be off as well). So changing the MAF curve requires a transfer function change. We do this on older DMEs, not yet on the OBD2 DMEs.

When changing the MAF curve, you can trick the DME. PiggyBack controllers, resistor packs,.. all are methods used to alter the new MAF signal to keep the DME happy.
Some use a higher MAF curve (lower signal for same air flow) and upgrade the injectors (and/or fuel pressure) to match the lower MAF signal.

If you must upgrade the MAF, the best solution is to alter the transfer function in the DME. This is not simple, so most people resort to external devices such as PiggyBacks.

Newer DMEs (as early as 944S2) do have all sort of tests in place. The MAF voltage under certain conditions is checked and compared to a fixed value. If incorrect data is captured, a fault mode is activated. Some newer cars use a MAP in conjunction to the MAF, meaning more checks and fault modes to deal with. Basically changing the MAF curve is just the beginning, lots of other things must be modified as well.

Going back to the original question. If you are maxing out the MAF at 4200rpm (5Vdc at 4200rpm), altering the signal can be done via a PiggyBack (you can even alter ignition if you want). You can use a MAF with a different curve (higher), but you will hame to alter the signal (via PB) to look the same as the early MAF except at higher RPM.

The MAF signal is used to calculate fuel, so you must check that the changes you are making will not hurt the AFR and will not trigger a fault mode (CEL).

If you have a question, feel free to drop me an email.

Edit: If you want to check the MAF output, get it from the OBD2, much safer than a voltmter under the hood. You will need a OBD2 reader, some are PC based and allow you to data log etc..

Jean

You should be here more often John! Even I understood your explanation.

fast951

Hi Jean, how are you? I had to rewrite the post 2-3 times to be as clear as i can LOL. It's much easier to do it than the explain it!

Jean

Great John, thanks. Very clear explanation..!
Seeing our Greek friend next week.

Thanks, Jean

Jussi

Yes, I know these calculations..
Things get funny if we calculate backwards..
If there would be 993TT MAF based 650hp version, that means
650hp / 8.5hp/lbs = 76 lbs/min !
which means 588 g/s ! - show me the datalogging where are RPM and these kind of MAF levels

I haven't got my stock MAF measuring over 406 g/s.
But it can also be broken or dirty.
That's why I like to see somebody's datalogging either MAF voltages versus RPM
or easier way:
OBD logged RPM and MAF (and speed, load, throttle) - like I did.

Maybe it's better that I publish my datalogging, so you can see what I mean and wiser guys can suggest what is problem..
Notice that throttle is fully down during whole acceleration even ECU shows differently (is this normal?) and MAF starts falling already from 330g/s..
993TT datalogging