MAF (Mass Air Flow) versus Speed Density, Discussion & Debate for ALL
 

Hi All,

There is definitely a debate going on right now between the two options available and I would like to start this thread in a light that is open to all sides for debate and discussion. The goal of this thread is to keep a friendly debate between the options/tuning solutions available, benefits and drawbacks of each from whoever would like to discuss the topic.

I will be taking the responsibility of keeping the debate on as even a playing field as possible and while I can not be an official "so to speak" I do want to hear the opinions of tuners and different tuning options available for each. So I will attempt to do my best at keeping things equally balanced. Moderators are more than welcome to review the thread to keep the bad-mouthing at bay.

So as the forum rules state, NO bad-mouthing other products, but you are more than welcome to offer difference of both systems. As a caveat if you speak about how an engine management system may work you are required to have used the system prior to speaking about it features.

Topic:
- MAF (Mass Air Flow - Quantity of Air) versus Speed Density (Manifold Air Pressure - Quantity of Air based on Pressure)

Current Tuning Options Mass Air Flow:
- BRZEdit
- EcuTeK
- Open Flash Tablet

Current Tuning Options Speed Density:
- EcuTeK - RaceROM

If you as a tuner would like to debate, please let me know so we can add you to the list of people officially debating. Also non tuners (members of the forum), are more than welcome to express their opinion also. Please offer a little background of yourself when giving your opinions.

Debating Tuners:
- William @ Delicious Tuning

Regards,
William Knose

Saving space for later use.

To bad this thread was created during a time that some people aren't allowed to post :)

Well to kick off, there's a great resource here - http://oldfuelinjection.com/?p=4 gives a good summary of the four types of fueling systems (MAF, SD, Alpha-n and the antiquated vain airflow).

About me - I'm an end user who took matters into his own hands, so to speak :D I'm well acquainted with the open source implementation of SD (both the initial one based on Freon's work, and subsequent significant upscaling of the implementation by Merp), both at a code level, and having implemented it on my own vehicle (09' STI).

My personal cliff-notes:

- MAF is much more versatile at adapting to dynamic environments (IATs, altitude, etc.). That being said, SD can be adjusted through various compensations to mitigate some of these issues.
- Flowing from the above point, idle and low load driving was much easier to tune using MAF, whereas SD (where IATs are a key input into the calculation of fueling requirement) could swing very wildly given small temperature changes.
- On the con side for MAF, once you start pushing serious power (I was logging over 500g/s in terms of load) you quickly max out the capacity of the MAF sensor - and hence it's resolutions, at higher loads. In the above example, I was reaching voltage of 4.92v (out of a maximum of 5v), and that was using an 83mm intake, well above stock.
- Along with a larger intake, came a number of other headaches with respect to tuning idle and low load, due to the changed flow characteristics of the charge)
- SD, in my personal experience (mileage may vary), once thoroughly dialed in at the top, gave me more consistent AFRs - and hence a little extra up top.
- Hardware, especially the location of the IAT sensor, is important for a decent SD implementation. You want the IAT sensor as close as possible to the plenum - in other words, reflecting the actual temperature of the air charge entering the chambers as accurately as possible. This is even more critical with forced induction due to the differing temps at the intake and the throttle body.

My 2 cents.

To start the debate, a question has been asked at what point does one need to use Speed Density? Is it at a certain horsepower level, or maybe something else?

Well, from personal experience there is not one exact answer. I have used both MAF and SD (Speed Density) over the years and many scenarios, where SD was useful, otherwise MAF was just as good in all scenarios otherwise noted.

Speed Density Benefits:

Head to Head Competition, where you will be battling it out on the track or similarly where walls are involved. So rally-cross, SCCA, or similar. The benefits are when the piping or intake get damaged you can continue running, and do not need to worry about falling out of a race. Now can you run MAF in these scenario's of course but there is that chance something could occur and knock you out of the race.

Non Head to Head Competitions, such as Time Attack, Rally or Hill Climbs where is a hose pops off, you will be knocked out of the race. The reason is the MAF sensor needs to see airflow and be in a contained system, which if is not, will show in-accurate readings to the vehicles's ECU and therefore will not run well if at all.

MAF Sensor Benefits:

Now on the flip side, tuning a vehicle for Pikes Peak with MAF is a LOT easier than Speed Density (though still completely possible), it does take time. When you are running Pikes Peak MAF will work rather well, in fact pretty amazing. I would even go as far as saying better than Speed Density.

So as far as say Pikes Peak, does one take MAF or Speed Density or vice versa? What are your thoughts? Think of it from a financial point of view for a race team and local Joe, because anyone can enter their vehicle to race up Pikes Peak with proper qualifications of course.

Cheers,
William Knose

I personally would be more than willing to have that person, and we all know who it is to post on this thread if the other tuner would allow it and moderators would be allowing to. So I ask the question, can we all agree to debate professionally.

Cheers,
William Knose

Ah yes, of course - forgot about that specific advantage as well - boost and vacuum leaks don't affect fueling calculation, and you can unleash the inner ricer (vent to atmosphere BOV are perfectly fine with SD).

I like all the information being shared. Everyone, the community, can benefit from non bias information. It will help me decide, with other things, if I'm going to FI my FRS.

What about piping freedom being a bonus to SD? Ive had MAF sensors act up and the tuners have told me its do to the positioning of the sensor, to close to bends or transitions. I do lots of fabrication of piping and some times its difficult to incorporate a long enough straight section to provide straight air to the MAF.

This is what it is intended for. So that you, the community, can make educated decisions based on professional opinions from tuners. Of course you have your local tuners you may be bias towards, but that is absolutely fine.

A great point. When I worked with Kraftwerks to tune their Rotrex supercharger kit they decided to work on airlfow and smooth bends versus making sure the MAF sensor was located in an ideal place. This has is benefits and drawbacks and because of this design we needed to be setup for Speed Density.

But after the initial tune was completed upgrading this kit down the road, will be a lot easier. And making big power with a Speed Density map should go quicker now, as I will not be limited by MAF resolution. Definitely a big plus for me personally on this setup.

Cheers,
William Knose

I wish I had a local tuner, I don't think they have any Subaru tuning shops in Louisiana.

to me it comes down to hardware. if i have a turbo with a 4" inlet, it would probably be a good idea to make the move to speed density and get rid of the maf. if i'm running a stock-size intake tube and haven't maxed my maf, i'd keep the maf setup.

it's not at all about which is 'better'. they are two different approaches to a problem, not a solution to one. the solution is the calibration in either case. it's just a matter of which method makes achieving that ideal calibration easier in a given situation, which i believe is all about hardware.

I would say that virtually everyone with FI(as far as I know) is running the maf as a "blow through" setup, so it really doesn't matter.
The vented air is unmetered and will not cause fueling issues.

This is only true if the leak is before the maf sensor. You could be leaking out your IM/tgv/block gasket or injectors or any of the IM ports that see vacuum / boost and it would be leaking metered air. Blow through does prevent a majority of the boost leaks you would see from boost tubes / couplers however.

Leaking metered air is always a possibility with MAFs.