think you know SRs?SR20DE+T MAF location

[1996sil80]

I am curious to know why nissan engineers located the MAF sensor "up stream" of the turbo and intercooler on a SR20DET.

Its a given that the charge air properties (density and temperature) will be effected by different turbo and intercooler setups.

Is it not important for the maf to read conditions of the actual compressed and intercooled air?

Are not the charge air properties entirely different from the ambiant properties at the filter?

What (if any) are the pros and cons of mounting the maf on the throttle body (or at least "downwind" of the intercooler)?

Domestic LS1 (EFI V8) Setups maintian the MAF on the compressed side of the induction system at the TB.

It seems reasonable to me that the RESISTANCE of the tungston (hotwire) of the maf would be GREATER on the charged side of the intercooler, thus passing a SMALLER voltage signal back to the computer for a more precise and appropriate mixture.

Charged air is typically hotter than ambiant air, unless there is a very efficient intercooler in use, and then that would be a factor to be considered as well, in reguards to a MAF voltage signal.
Modified by 1996sil80 at 7:35 AM 8/8/2008

[tctomasc]

I would think it would have to do with heat of the air. Too much heat can burn up a maf? I mean I don't know how most turbos have it set up, but i definitely know N/A's with mafs considerably far away from the engine, and keep reletively cool.

[1996sil80]

it is my understanding that the very essence of a hot-wire MAF is to send a signal to the ECU based on ultimantly on the temperature of the MAF wire.

I i install a VERY EFFICENT intercooler with spray bars, then the charge air will be very dense and the computer will not know to add more fuel for the super dense air......

[1996sil80]

but i guess thats where the 02 sensor comes into the picture. but then, it STILL negates the purpose of the maf in the 1st place if you are going to correct it with an 02 sensor....

[Hijacker]

The O2 is for fine tuning the fuel mixture. It only sends an on/off signal to the ECU in relation to the outgoing exhaust gasses. I can run a car without an O2 sensor, but I can't without a MAF.

The reason the MAF is designed to be upstream of the turbo is due to heat issues. An MAF's job is to measure air volume. By putting the MAF right behind the filter, it can read the air pre-compression and be able to accurately relate the volume of air as it passes through.

MAFs don't have pressure sensors in them (or else they'd be MAPs, not MAFs), so a MAF wouldn't be able to tell the difference between 5 psi and 10 psi. It could just tell you "x" amount of air has passed through because it had to use 'y' voltage to keep its heating element at optimal temperature.

There have been successful blow through MAF setups done on 240s. You should search for them and read up on them on google. I for one, don't like them due to higher failure rate and the ECU has to be programmed for not only injector size and MAF type, but it will have to be tuned to recognize the flow/boost characteristics of your turbo. It's just easier, simpler, and you have longevity on your side if you run the MAF in stock location

[1996sil80]

thats closer to the the answer that i'm looking for! thanks! i am going to read up on "blow-through MAFs" (i didn't know there was a term for them)

if i have more questions after research, i'd like to discuss this with you. you sound knowledgable!

respectfully,

Adam Smetak

[1996sil80]

this thread about mustangs knocked my question out of the park!

http://www.mustangforums.com/m_3233163/tm.htm

thanks for the help with terminology (blowthrough / drawthrough)

Adam

[Cone Junky]

Just to add to the well put logic, the charged air that is forced into the engine also has a quantity of oil vapors in it. Oil and MAFs don't mix well.

[Hijacker]

Just to add to the well put logic, the charged air that is forced into the engine also has a quantity of oil vapors in it. Oil and MAFs don't mix well.

Very good point!

[vanquish2]

Nissan along with all other manufacturers do not intend on anyone highly modifying their vehicles. They engineer their design to work well with THEIR setup and THEIR programming...and possibly with the SR they may have also tuned according to THEIR regions weather based on the fact of it not being sold to all parts of the world. They may have also tuned based on available fuels in their region.

Also, many a tuner have said that it is much easier to tune a maf system on a suck through oppsed to a blow through system. Maybe simply due to the fact that it is how Nissan design the programming....compensating for the difference in loads and assuming certain property differences from intake versus charge temp, pressure, etc.

Something else to consider is that many people especially in the import world will chose to switch to a map system when greatly exceeding the manufacturers base HP. I.E. Supras

Just a couple thoughts