These are the inputs I'm looking for. I agree with all the comments so far, and they are how I understand MAFs to benefit - namely optimizing the tune for max efficiency. I am in southern CA, and I agree, the weather is very stable even across season an little elevation change.

That said, I'm looking to dig deeper on this topic then generalizations. MAFs are also great for setup changes and modifications that affect VE. Such as slapping and exhaust on, or the addition of an intake. But these can be affected by custom tuning too.

Thinking out loud...

Another condition is VE changes due to mechanical issues (i.e. leaks).

With MAF, if there's a leak post MAF, under vacuum conditions, fueling will likely go lean. Under boost, it'll be rich.

Without MAF... it might actually be more resilient to leak conditions?

 

MAF does adjust to vE changes better since it measures rather than infers airflow. However the measurement device can be fragile and restrict airflow. It also means that at some point all of your air should go through it. You can split the airflow and only measure half but if one side is more restrictive or has an issue things could get out of whack. Air leaks with a MAF or vent to air BOV can cause issues too.

I've honestly not ever tuned a MAF system and am pretty curious as to how it differs but most aftermarket EMS are speed density - make of that what you will. Getting a good calibrated MAF can be expensive and as I mentioned before high power capable ones will be less accurate at lower air volumes. Pro-M would be one of the few manufactuers I've ever seen that give info on their meters but I'm far from thrilled at the way they and others sold meters designed to "compensate" for different injectors. This is a truly stupid way to change a tune as it screws the ignition tables - a pet peeve of mine lol. Pro-M have some interesting vids on their site explaining how MAF work and tuning with them.

 

Remember guys, most new cars including 991TT's are no longer using MAF meters. They use a lot of variables to calculate air flow and monitor everything including simple air/fuel. At the same time it can be argued that if the MAF has the capacity it's nice to have. So far I have had a 100% success rate running cars MAFless with Cobb. Your tuner should be able to figure out what will work best for you and your situation and with your tuning solution. My .02

 

Very interesting that the 991 have moved away from the MAF meters, I'm betting the CPU in their processors is pretty fast. The ECUs I've seen have generally been slow compared to desktop CPU so it only makes sense they could step it up if they wanted. What are they using aside from IAT and a MAP sensor I wonder. I don't know how COBB or anyone else is converting the stock ECU to MAFless but I've ridden and driven one (although not COBB) and had I not been told I'd have assumed it still had the stock MAF in it - and I'm picky! So I have no doubt it can be done and done well, it's nice to see that COBB is making this so much more accessible as dumping the FEET of intake piping on these cars has got to be worth noticeable horsepower...

 

Great discussion and I learn more each day. BLKMGK, I'm with you on the intake mod potential of losing all that convoluted piping with a MAFless tune. This is really starting to open up another chapter for 996 tuning with MAFless tunes readily accessible and to great effect. Perhaps all this Hatachi MAF talk is moot?!

Sam, I'm totally confident in your recommendations, which is why I picked you as my tuner! Though I'm an engineer at heart so I still like to dig in and learn. BTW, motor is making it's way back into the chassis this week. Can't wait to fire her up with the new injectors and tune.

 

Cheers guys. Thinks just keep getting better on the Porsche platforms! Can't wait till you get her running!

 

Yes, a MAF will aid in reducing emissions, but it is about ultimate efficiency - not just about emissions. You could make a 996tt run fine with 1 large carburetor (driveability-wise). But you'd be making less power, your fuel economy would utterly suck, and you would never even get close to passing even the most lenient of today's emissions tests. You could improve all of the above by metering fuel more accurately with a pair of triple Webers, and even more accurately with mechanical fuel injection such as K-Jet. And so on (the abbreviated history of Porsche induction systems LOL). And, in theory, you could even tune one large carb to perform as well as a modern FI system - but only in one environment and at a given RPM. As soon as you start changing any variables - even something as basic as RPM - the carb could no longer compensate accurately.

Anything done to improve accuracy in fuel metering in all conditions improves efficiency in all conditions. So for a daily driver driven at cold and warm temps, different altitudes, over longer periods w/o intensive service, etc, etc, removing the MAF is removing the single most effective sensor in calculating fuel metering - and, as such, a step backwards IMO.

If you are building a 1/4 mile car, go with the KISS principle and go MAFless. But even here, to reach the final few hp, you will need to monitor the weather and adjust your fueling accordingly.

A MAF is not the end-all solution, tho. Hot wire MAFs came out in the 80s (!). But the 996 FI was designed around this principle. I've not even taken the smallest of glances at the 991 FI system, but I am sure it is more accurate than earlier systems even without a MAF - but it was designed and built that way. Equating removing the MAF in a 996 to an improvement because the 991 has no MAF is akin to saying: a '69 Chevelle works great with a big block, so get rid of the horse and strap one in front of your buggy (sorry Sam ;-p).

 

Lol, no apologies needed. The forum is for opinions and experience to be shared. This is proper load sensing MAFless. The car is a lot of sensors to aquire and calculate information with. Whether it's super cold or super hot, and the exhaust you throw on her and whatever altitude you go to the set up works end it has. There are literally hundreds running around. There are also some with oldschool MAFless conversions that never worked right. Cup cars for example are pissy for drivability and hot blooded. Those days are over and there are only two companies that can do it proper on the 996 and 997 on the stock computer following models from the new cars. Now I played a lot in high school but never figured how to rebuild a carburetor and adjust it properly. I would be willing to let anyone try it. They can data log their car before and after and check it out. That's the beauty of the Cobb AP.

 

Single most effective? Until you make more power than it can meter. Until you put in one large enough and end up with a meter that can no longer efficiently meter at low airflow. Or until you realize the hoops you jump through with something like 5FEET of intake tubing is crazy. Or until you start popping them like flash cubes. Or until you get one that's calibrated incorrectly and the car runs like crap, finding genuine Bosch is getting harder now that they counterfeit the hologram stickers.

You keep mentioning altitude as if MAP sensors don't measure that out of the box. I once drove a MAF car up a mountain and nearing the peek it ran like crap. On a hunch I turned it off and back on, ran fine. Why? The MAF sensed ecu got altitude readings from a MAP sensor but only at startup. MAF cars often come equipped with MAP sensors for this reason open to atmo to get readings, they just don't always continuously sample them!

If you know VE, if you know intake temp, if you know pressure - you have what you need for airflow calculations to create a fuel pulse. It's math, somewhere I've got a textbook with the calcs but generally I leave it to my ECU to solve this. I took a tuning class and we measured these things to calculate injector pulse for a specific A/F ratio, then measured the injector pulse with an oscilloscope - it was spot on. This stuff isn't done on a hunch.

Weather changes? You mean temp and pressure? There's sensors for this I've already mentioned. Properly tuned you won't have to change a thing to compensate for weather as this isn't a carburetor. I'm not sure how carbs came into this, that's apples to oranges and doesn't apply. (shrug)

With proper tuning capability there's no reason not to remove the MAF and it sounds like COBB has it covered. Once you get past a certain HP level you're no longer using the MAF anyway, why live with the restriction?