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Guest Message by DevFuse

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Philosophical Tangent! MAF focus

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4 replies to this topic

#1 electryc_monk


    Air-ride Airehead

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Posted 30 October 2003 - 10:26 PM

What is the reasoning for placement of the MAF before the turbo?

I just had a wild hairbrained thought! And really and truthfully wonderd about the systemic problems that might or might not be of issue by placing the MAF at the mouth of the intake AFTER the turbo (and once installed also after the IC)?????

Well folks any thing I'm not realizing with respect to air fuel ratio and the like? Considering the ECU is running off the thermal reading in the air (if its a hotwire version that is) and if its getting the data from after the turbo then wouldn't the reading be more accurate then before the turbo given the temperature differential?

Could the system be simply set to WOT fore less scripting in the ROM chip for the EFI computer? And if the movement of the MAF to after the turbo (and IC) wouldn't this also allow for a interesting place for it considering the more versitility of an intake to the turbo from who knows where at this point?

Or am i just utterly forgetting a very important factor of internal combustion system dynamics?

#2 archemitis


    guy smiley

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Posted 31 October 2003 - 09:51 AM

go look at some 900 horsepower japanese supras, and skilines, and all those. the reason you always see down the throat of the big fat turbo is not because they all use maP sensors(some do) but its because they moved their maF to where you are talking about.
just think, your maf thinks that the air going into it is outside templ, but by the time it gets heated up, and cooled down agian, there has to be some issues.

wouldnt a flapper door be better for that reason, it measures volume. instead of the hotwire, that just measures cooling effect.

would be cool to try. it would work for sure.
but think what would happen when your turbo started leaking oil.

#3 Nug


    Lurker/off-topic poster

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Posted 31 October 2003 - 11:03 AM

Here's something I can't figure out. Why (sometimes) are oxygen sensors located downstream of the air injection ports? I mean, you are trying to measure the amount of oxygen left in the combustion gases, right? And injecting a bunch of air before the sensor is going to add extra oxygen, right? It's gonna throw it out of whack.
Subes don't even have smog pumps, do they? So for most of you, this probably isn't an issue.

#4 rallyruss


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Posted 31 October 2003 - 12:41 PM

Interesting thought and it might work if you are into reprograming ecu's ect.
I would not try it for a few reasons.first the air temp sensor is built into the maf and would be verry confused as to what actual inital air temp is. second the efectivness of the hot wire set up would be compromised. it calculates air flow by how much the passing air cools the heated wire. it most likely would cause an error on the lean side. not good:eh: .

to answer snot rockets question. air injection on the cars you are speaking of works on cold start up to help warm up the cat. the O2 is still sleeping untill after the air injection shuts down.

and yes older subes had pulse air injection used with carb setups.

#5 Setright


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Posted 01 November 2003 - 04:42 AM

Ermm, a hot wire MAF is very accurate. The flapper door system is better than nothing, but it has moving bits that wear out, and cause misreadings.

As for the location...well air only enters via the intake right? So how would the VOLUME of air change along the way? The MAF gives the ECU an accurate indication of how much air is available, and the ECU tells the injectors to do its bidding. Then, the O2 sensor is used to make sure things went as expected.

It's a very reliable system, and I wouldn't mess it. There is no need to subject the MAF to the higher air pressure aft the turbo.

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