air flow theory...

[koolade9]

correct me where I'm wrong...

okay, the mas meters the incoming air, it's boosted, cooled, sent throught the upper ic, intake, and fuel is added... that whole round trip is like what, 8-10' or so all together, and if it's bled back into the system via bov, that air travels another 6-8 feet or so before that "metered" air gets to the bottom of the intake manifold, now I'm assuming the ecu knows roughly how long the path is from the mas to the intake for a good a/f mixture, but if that bov is open at all...there's no way for the ecu to know that, and now it's sending fuel to air that isn't there(does that make sense?)...or am i missing something?

so the obvious solution would be to move the mas as close to the throttle body elbow as possible to eliminate the bov condition...but, if the ecu still thinks the air has to travel a certain distance, it's now sending the correct fuel "late"

any thoughts on this would be great... obviously this is a "daily drivability" question, as WOT, would not need worry about how far the air is traveling because of the overlap involved with the a/f timing(I'm assuming).

if this doesn't make sense, i appologize. I can visualize the whole deal, but I haven't had the tuning experience to answer this myself.

comments, thoughts, and corrections are greatly appreciated.

 

[98TsiAWD]

The stock ECU has WOT fuel curves that enrich the a/f ratio at certain airflow/rev. The High enrichment (55% more fuel I believe) kicks in a ~2.10 airflow/rev. It wouldnt be getting there late or anything like that.

But you are right, putting the MAS right before the t. body is a much more accurate way and should net you some hp when you tune vs. a stock mas setup.

 

[koolade9]

okay, that's kinda what i thought... basically, because the system is essentially vacuum based, what happens at the mas, is what's happening at the runners of the intake...therefore the timing doesn't become an issue...

so now the new ?... I've only seen people run the gm maft between the bov and tb elbow, and that's on 1gs. Has anyone relocated their stock 2gmas to that location?? It looks like the harness is long enough, making it really a plumbing issue....I can't be the first to attempt this???

 

[gixrman]

You are coorect, the ECU already takes into acount the air that has already been metered going through the stock MAS and then recycled by the BOV in a stock situation. If you look at the 2g setup the dump tube is pointed directly at the tubine wheel, the treory being it would help in spoolup. The "blow though" set you are taking about with the GM 3" MAS and the translator has been done by several people on here and pic. can be found. No one makes an aftermarket setup UICP that I know of yet for a 2g.
If you put the MAS after the BOV you can vent to atmoshere, thats your only adv. and maybe faster spoolup. You just have to come up with the custom plumbing.

 

[kpt4321]

The stock MAS (1g and 2g) is built to measure un-pressurized air, so you can't put it in the upper IC pipe.

There is no problem with timing. When you open the throttle, the air has to go through the MAF before it can go to the motor, but, you have to keep in mind...you don't have to wait for the same air molecules to get there!

If you open the throttle, the air starts moving through the intake tract, meaning that the air is going through the MAF faster (more airflow) at the same (or similar, not exactly the same) time that the air is moving through the throttle body faster. That doesn't mean that the air has to go all the way from the filter to the motor, because there is also a bunch of air already in the intake and IC piping that can be used!

 

[13secGST]

yeh, all the air going to speed up at relatively the same time when you open the throtle...and you will get more air and fuel at that instant...not when the air that was measured by the meter at that instant gets there...

 

[Mike Licht]

The ECU has NO idea of how long the path length is and it does not matter. Once the air is mesured it moves in a steady column like water through a straw. That is all it needs to know. there is no compensation for that.
Mike Licht

 

[Groomz]

www.dejontool.com makes a 2G blowthrough setup.

 

[jb talons]

http://www.slowboyracing.com/Intercoolers/IC pipes/2g MAF/2g_maf.html

Another 2G blow throughset up.