Why run a MAF?

[johnmaster]

Hello, New to tuning, not new to technology, cars, or DIY projects. I have been thinking about this for weeks and can't seem to find a definitive answer anywhere. Why run a MAF sensor? What applications does it help you and what are it's limitations (i.e. when would you be better off not using one?) Applies to all but I am planning to turbo a 5.3 and am trying to decide if I need to start looking for an IAT sensor or accommodate a MAF/IAT in my charge tube design.

[Slowrc]

I look at a maf as another input to the pcm to better determine fueling. On a 5.3 with 7 psi keep the maf. if you know you'll be boosting way more. Use a COS and a 2 or 3 bar map and a seperate IAT sensor. This subject has been beat to death on many forums. Google (Boost maf ls1) and you can read opinions for days. BTW, A boosted 5.3 is FUN!!!

[SSpdDmon]

Short answer is, because the MAF is a tool that's used to MEASURE airflow. SD is a CALCULATION of airflow based off of other known conditions (RPM, MAP, Temp, etc.). Although you can run the numbers through the formula and be right most of the time, it's my understanding the MAF is a little more flexible/accurate because it's measuring what's really happening.

[johnmaster]

Ok, so basically I am getting that if my application falls into the range where the MAF still functions properly, it's more accurate and can make fueling more precise, but once airflow increases past that point its better to ditch it and use the MAP to calculate VE instead. My application will be the latter, I am planning on needing a 3 bar map. I'll google it and see what else I can learn but this sounds like what I needed to know.

Do I need anything specific for the IAT sensor. If all GM sensors send the same output is this one as good as any?

For a carbureted turbo application should I mount it in the charge tube or in the intake manifold? I may want to put one in each and log the differences...

[mr.prick]

Look in the .tun and you will find there are tables based off MAF reading.
COS is in your future.

I look at a maf as another input to the pcm to better determine fueling. On a 5.3 with 7 psi keep the maf. if you know you'll be boosting way more. Use a COS and a 2 or 3 bar map and a seperate IAT sensor. This subject has been beat to death on many forums. Google (Boost maf ls1) and you can read opinions for days. BTW, A boosted 5.3 is FUN!!!

7psi isn't enough to max out the MAF scale in a GEN 3 controller?
I've seen logs where the 1bar MAP is nearly maxed N/A and
my old N/A setup reached 80-85% of the MAF scale at mile high altitude.
N/A = 1 psi?

You can fudge the MAF/VE table data with IFR but what happens when the MAF Hz/MAP kPa limit is reached?

I would think the MAF is the least of your worries.

[redhardsupra]

you run out of MAF, you switch to SD. Then you run out of IFR. Even if you do a good job on that, then you still can run out of RPM. at one moment you actually need to abandon ship and graduate to a Motec.

[Mr. P.]

...Why run a MAF sensor?

Assuming a Gen-III motor - because you want to keep the vehicle smog-legal, and have it cope better with changes in weather and/or altitude. However, the weather/altitude issue can be solved if you invest the time and really dial-in your VE tables & other supporting tables to account for all operating conditions, in fact lots of guys running mafless will tell you their vehicles run far better in SD than they ever did with the MAF, not necessarily because the MAF is worse but because they invested the time after removing the MAF to get the PCM tune dialed-in correctly. For comparison, on 6.0L truck motors we don't consider abandoning the MAF until the engine is breathing more than 8psi boost.

If you are customizing your own charge tubing, I would suggest you ditch the MAF if emissions inspection is not a worry; the reason that I say is, a MAF requires dead smooth airflow to read correctly, and in a lot of custom piping jobs you have blowoff valves, bypass valves, bends, Tees, etc that will cause turbulence across the MAF and you will have to get rid of it anyways because it won't work worth a damn. An example, we had a '03 Silverado SS with Procharger P1 & a big-ass ATI bypass valve, and the installation & packaging of all that stuff underhood meant that the ATI bypass valve was 6-inches 'upstream' of the MAF and that totally pooch-screwed the MAF (turbulence in the charge tubing).

And Slowrc is right, you can make big numbers with a 5.3 & boost; since they have the same crank as the 6.0L motors they act exactly like a LQ4 or LQ9 when you put the squeeze to them, in fact better because of the increased charge density due to smaller cylinder volume. Watch your timing!

Mr. P.

[johnmaster]

I agree, packaging and airflow are my problems and running Mafless is what I am convinced (now) that I want to do. Tuning time is not a problem, I have time. I am not the end user who just wants to drive their toy to work and back, I am essentially a developer who wants to understand every facet of why their toy works as well as how, and how to reproduce it for others if need be. I have a chassis dyno that I can rent time on but I am worried about throwing myself at the mercy of the house tuner as I have a unique build AND I want to know every facet of what I am changing as well as why. I am thinking now that I ditch the idea of a MAF and just use an IAT and build a speed density tune from the remaining variables that I have left. Can anyone point me to some "how to tune for SD" threads that will help?

The application is 99 Chevy 1500 2wd pickup turbo carb. Eventually I will want to figure out how to do this to a DBW 03 and newer truck.

[johnmaster]

Smog legal not a problem, planning on lots of boost capability.

[Mr. P.]

Good discussion. From what you have shared, yes ditch the MAF and go SD, you are going to outgrow it in time.

Another perspective I have - coming up with a "complete" calibration for a vehicle takes TIME, lots of it. And most professional tuners don't have the time - most cannot afford the time, some are swamped with customers, and others are lazy. You can shortcut the time issue with what I call "template tunes" but those are just starting points and a tuner needs to continue from there to really dial-in a vehicle, and that takes more than just 30-mins of "live seat time" in the vehicle. As a consequence of that, my belief is that a significant number of professional tuners come to rely on the MAF to do a portion of their tuning for them, so to say...

I totally understand your saying "at the mercy of the house tuner", you and I are very like-minded. My problem is that in the DFW area all dyno owners either don't tune GM vehicles (they do exotics, imports, or Mustangs), or they use HPTuners rather than EFILive; there is one tuner in this area that does use EFILive, and his dyno facilities are fantastic, but the dyno owner requires that you employ his tuner (rather than you tune it yourself) and feedback from other customers and racers is that they get a proper WOT calibration but the other 90% of the tune required for daily driving just sucks, and you pay hundreds of dollars for that suckage. :( And like you, my quest for internal combustion knowledge pushes me to learn DIY-style, hopefully without pushing a rod through the side of the block...

I gotta ask - why a blow-through-carb approach, rather than a blow-through-EFI approach?

Mr. P.