MAF discussion anyone?

OnyxEros · 03-02-2005, 06:20 PM

I have been reading more and more about MAF vs MAP sensors and I am putting a few things together that I thought I would share.

The basics of our MAF system is a "hotwire" Our ecu is programmed to keep a thin wire (platinum?) above a certain ambient temperature. Air passes over this wire and the ecu increases voltage to heat the wire to the desired temp. The amount of voltage needed then calculates the air density going into the motor.

The best ting about this is that it's self correcting. So in theory I can run a 2L motor do a few tweaks to the ecu and then run a 2.1L motor with very little headache.

I believe this is one of the reasons nissan guys are ok with sticking with JWT piggybacks before jumping over to standalones. I don't know specifically how they have caluclated what is a 'generally' good program for 3bar turbo or 11CR n/a but the ecu will learn somewhat on it's own.

If you have deeper insight into MAF's please share.

hpro123 · 03-03-2005, 06:16 AM

Correct in the how-it-works assessment.

The self-correcting part emanates from the fact that MAFs directly measure (approximate is a better verb here) Mass Air Flow. MAP-based systems on the other hand measure something else and it is up to the ECU-code to calculate the "equivalent" Mass Air Flow by applying predefined transformations to the info it receives from the MAP. The "predefined" here creats the "headaches" when upgrading MAP based system. You need to redefine them!

The "defects" of a MAF when compared to alternatives are few:

1. Price-Price-Price. OK that was one.

2. The fact that it absolutely-definitely needs to reside on the actual intake tract and this may create problems or restrictions in the airflow. It also needs to reside somewhere in the intake tract where the air-flow is smooth so it can measure properly. This "places" it a bit further down than the air-filter.

3. Sensitivity to foreign substances like oil from an air filter.

4. Finally, range of air-flow mesurement supported by the MAF may be a restrictive issue when upgrading. You cannot measure more airflow than the upper limit of the MAF so if your engine's potential is higher than that you NEED to change the MAF. ANd you must use the smallest MAF that supports your HP needs since going to a larger size would make you loose resolution/accuracy of the measured values.

Chris

spdracerUT · 03-03-2005, 12:02 PM

Quote:

Originally Posted by OnyxEros

The basics of our MAF system is a "hotwire" Our ecu is programmed to keep a thin wire (platinum?) above a certain ambient temperature. Air passes over this wire and the ecu increases voltage to heat the wire to the desired temp. The amount of voltage needed then calculates the air density going into the motor.

Actually, the MAF measures MASS directly, not air density. This is very nice because your A/F ratio is based on mass.

The MAP system works by measuring the air pressure in the manifold and the air temperature to calculate an air density. And then based on the engine speed and known volumetric efficiency of the motor, it can determine the volume of air going through the motor. So once it knows the volumetric flow rate of air and the air density, it calculates mass and figures out the a/f ratio.

That's the problem with modifying Hondas. You change the intake, exhaust, or cams on the motor and you change the volumetric efficiency. But if you haven't adjusted the fuel maps to take that into account, your a/f will be a little off (or a lot depending on how extreme the mods are).

Anyways, i think that's all correct.

As for reasons to switch to a MAP system. Well the MAF is a flow restriction so when you start talking very high levels of HP (like 700-800whp+ or something) and you're trying to eek out all the HP you can, you'd use a MAP system. And at this point, you would've spent the dyno time to make sure the engine management is tuned properly

MAPs work really well once they're tuned correctly. If you make a change to your setup though, you'll need to retune moreso than a MAF based setup.

Calum · 03-03-2005, 01:24 PM

Quote:

Originally Posted by spdracerUT

Actually, the MAF measures MASS directly, not air density. This is very nice because your A/F ratio is based on mass.

Actually, it measures mass FLOW, not mass.

Another way to look at it is it directly measures the VE of the engine.

hpro123 · 03-04-2005, 04:55 AM

Quote:

Originally Posted by Calum

Actually, it measures mass FLOW, not mass.

Another way to look at it is it directly measures the VE of the engine.

Semantics Calum, semantics..

Strictly speaking though, you are absolutely correct! After all, it IS called a MAF sensor (Mass Air Flow) and not a M sesoer or an AD sensor (air density)...

Chris