LS1 MAF Selection

[32deucecoupe]

So the 04 GTO dropout that I bought did not come with the MAF, when researching I see that replacements range from stock to very high flowing units, since this engine will stay basically stock in nature would I see hp gains with a higher flowing MAF? Any recommendations.

[T_Raven]

Have you considered switching to a speed density tune and not using a MAF? It's a common thing, though I don't know if there are any draw backs. If you're going with a custom tune it would save the cost of a MAF and simplify your intake set up. If you're staying with a stock tune, you might as well use a stock MAF

[32deucecoupe]

It will be a custom tune, I have yet to order my harness but will need to identify all of my modifications prior to the tune, at least that is my thought process. I will definitely look into the speed density tune, I had not heard of that before, plus not buying a MAF will cover part of the tune cost

[jlcustomz]

I still hear there are some drawbacks. Factory uses both map & maf for signals.

[GeoffP]

The biggest drawbacks I know of resulting from removing the MAF from a tune is that depending on the new tune you can lose minor drivability, fuel economy, and I know for sure (from experience) the engine won't be as cam friendly if you decide later to install a bigger cam. A MAF will help the ECM accommodate a bigger cam without requiring a new tune except if you just want to maximize performance by getting a new tune. I'd think you should be able to find an LS1 MAF fairly low cost. Remember to think long term so you're not spending twice (again from experience) because it'll cost you more in the long run. I hope this helps you in some small way!

[mitch_04]

The biggest reason I see to keep the MAF vs speed density is that the MAF is actually measuring the amount of air entering the engine. Like Geoff said, this will make it easier for the computer to compensate for changes without a re-tune.

The speed density system uses fuel tables that you (or the tuner) set up, so when it sees x-amount of vacuum, it injects x-amount of fuel. If you change anything that makes the engine take in more air, whether it is better heads, a cam, or just a cold air intake, the tune would need to be redone because the engine is now more efficient at the same amount of vacuum that it was previously.

The downside to the MAF is that it is capable to max one out. If you end up modifying the engine more than you thought you would, you would have to upgrade your MAF.

[wizbang]

The downside to the MAF is that it is capable to max one out. If you end up modifying the engine more than you thought you would, you would have to upgrade your MAF.

Hey Mitch,

Would you elaborate on what you mean by maxing out the MAF.

Thanks

[mitch_04]

Alright, I'll give it my best shot but I'm not always the best at explaining things. Lets say you have a stock engine and you throw a turbo on. You are now flowing much more air past the air flow sensor. The MAF may be able to measure more air than originally, but eventually it will "max out" and only read a certain amount once past its "max". You then upgrade to a different sensor that is calibrated for the larger amount of airflow OR you can adjust the MAF settings in the computer to do a scaled reading. The scaled reading, IIRC, is somewhat frowned upon because you are now using a multiplier and not going off the true reading. Whenever you upgrade MAF sensors, however, you have to put the new settings in the computer.

Mass air flow sensors work by having 2 heated wires that are cooled by the air going by it. The one wire is a more of a constant and the other is the variable. The computer judges the amount of amperage required to heat the variable up to the same temp as the constant and determines airflow through calculations predetermined by engineers much more intelligent than myself.

Different MAF sensors operate differently and this is being described as best I can without referencing anything so it maybe slightly off. If you want a couple of great books, search for Matt Cramer (one of the engineers for Megasquirt) or Greg Banish (engineer for a few major companies). They have both written books that have increased my knowledge of fuel injection more than 2 years at college for auto repair ever did. I think Matt's is more regular-joe friendly, while Gregs is slightly more technical. Also, Greg's advanced book, I thought, was easier to understand than the other. Go figure!

Hope this helped some.

[wizbang]

Thanks for the information, Mitch.

The reason why I asked is because I was unsure if you were referring to the MAF maxing out due to the MAF sensor not being able to produce higher readings or the MAF maxing out the values that the ECM can interpret.

From my experience with the Ecotec 4 cylinder engines and the 3800 V6 engines, the MAF sensors with these engines can read air flows beyond with the ECMs can handle. The MAF sensor readings that are sent to the ECM is Frequency modulated. The ECMs in these vehicles can only receive frequency values up to 11,500 Hz. The MAF tables in the ECM can not be programmed with values higher than 11,500 Hz. However, the MAF sensors can continue to measure air flow up to 13,500 to 14,000 Hz.

For these engines, when they are maxing out the MAF, the MAF is running off the MAF tables in the ECM. Even though the MAF can read the higher air flows, the EMC can not handle the higher MAF readings. What we’ve done to allow the MAF to handle the extra air flow is to rescale the MAF sensor with an external Air/Fuel Controller (AFC). The AFC is wired in between the MAF sensor and the ECM. The AFC is programmed with scaling factors that are applied to the sensor readings prior to being sent to the ECM. For example, the MAF sensor reads the air flow observed and produces a reading of 12,000 Hz. This reading is received by the AFC. If the AFC is programmed with a 80% correction factor at 12,000 Hz, then the AFC sends a 9,600 Hz (12,000 * 0.80) signal to the ECM. This allows the ECM to be tuned with engine the breathing a lot more air than it would otherwise be able to be programmed for. Since the volumetric air flow grows approximated with the cube of the MAF frequency (Hz^3), the amount of air flow available from the MAF reading above 11,500 Hz to 14,000 Hz is huge. This enables the engines to run MAF sensors and produce HP way above stock levels.

What I don’t know is what is the highest frequency the MAF sensors can produce for the various MAF sensors typically used on LSX engines. Also, what is the maximum frequency that the various ECMs can handle. Hopefully you or someone else can chime in with this information or point me to where I can find it.

Thanks again.

[mitch_04]

I thought there was a website that listed various MAF "settings" but I do not know if it listed the frequency max. It was quite a while ago, when I was going to put a 6.0 in my project (it has since changed to a 3.5 inline 5).

[32deucecoupe]

So this grew into a lot more detail than I think I understand, which is what is great about this site.
Is the gist of this to make sure I size the MAF to not only accommodate my current air flow needs but also my potential future increased airflow needs and programmability. Right now as I understand it the 2004 GTO uses the LS6 intake with a 85mm throttle body and MAF. Since I need to buy the MAF anyway should I spend the money to increase both pieces in size to 90-100mm due to running headers and a cat free exhaust. I want to spend once as Geoff stated.