maf idea

[i2koldi]

ok so the gm maf lets you blow through so what if you moved the 1g (cause thats what i have) maf, to after the bov so that you dont have to buy the $300 maft and a extra safc or dsm link to tune, just the safc. the only big problem I see is the air restriction when tring to make big power. I was just thinkin and havent ran accross this idea yet so i wanted to get some feedback, because you have to admit if it would work it would save alot of money.
















darn dsmers always tring to find a way to cut corners on price

 

[VelocitàPaola]

This is one of those ideas where it's so simple, that if it worked, someone would have done it a long time ago. I don't know exactly why, though, it won't work. MAFs work by directly measuring flow rate, which is independent of air density (boost/vacuum). Theoretically, then, it doesn't matter if the MAF is before or after the turbo. Can a 4G63 guru fill us in on why this won't work? I'm interested...

 

[xveganxcowboyx]

Damn, I've read up on this, but I can't seem to remember the reason either. Though it's a good one. You definitely cannot use a stock style MAF in blow through setup. They are Draw through only.

If you search you'll find the answer I've seen the question asked around here before.

 

[jking29]

If I had to guess why this wouldn't work, I would say that the honeycombs are too fragile to handle boost.

 

[4g63t]

so that you dont have to buy the $300 maft and a extra safc or dsm link to tune, just the safc

???????

 

[Jeff_Ciesielski]

The idea wont work because DSMs use karman vortex style mafs.

" The karman vortex sensor works by detecting the frequency of small vortices that happen when a smooth airflow is presented with an obstruction. The number of vortices is proportional to the velocity of the airflow (I believe it follows the form frequency = kv^2). When the MAF outputs a “Hz” signal to the ECU, what you are really seeing is the frequency of these vortices inside the upper chamber of the MAF."

There wouldn't be 'vortices' in the same sense because the air would be flowing smoothly over the comb under boost, thus rendering the reading innacurate and useless.

jeff

 

[jking29]

The idea wont work because DSMs use karman vortex style mafs.

" The karman vortex sensor works by detecting the frequency of small vortices that happen when a smooth airflow is presented with an obstruction. The number of vortices is proportional to the velocity of the airflow (I believe it follows the form frequency = kv^2). When the MAF outputs a “Hz” signal to the ECU, what you are really seeing is the frequency of these vortices inside the upper chamber of the MAF."

There wouldn't be 'vortices' in the same sense because the air would be flowing smoothly over the comb under boost, thus rendering the reading innacurate and useless.

jeff

Nice answer! Learn something new every day.

 

[adrian2627]

has anyone ever done this before just for shits and giggles?

 

[andymoraitis]

The idea wont work because DSMs use karman vortex style mafs.

" The karman vortex sensor works by detecting the frequency of small vortices that happen when a smooth airflow is presented with an obstruction. The number of vortices is proportional to the velocity of the airflow (I believe it follows the form frequency = kv^2). When the MAF outputs a “Hz” signal to the ECU, what you are really seeing is the frequency of these vortices inside the upper chamber of the MAF."

There wouldn't be 'vortices' in the same sense because the air would be flowing smoothly over the comb under boost, thus rendering the reading innacurate and useless.

jeff

Bingo. Nice post Jeff.

 

[VelocitàPaola]

The idea wont work because DSMs use karman vortex style mafs.

" The karman vortex sensor works by detecting the frequency of small vortices that happen when a smooth airflow is presented with an obstruction. The number of vortices is proportional to the velocity of the airflow (I believe it follows the form frequency = kv^2). When the MAF outputs a "Hz" signal to the ECU, what you are really seeing is the frequency of these vortices inside the upper chamber of the MAF."

There wouldn't be 'vortices' in the same sense because the air would be flowing smoothly over the comb under boost, thus rendering the reading innacurate and useless.

jeff

Actually, I was intrigued, so I looked this up... Karman vortices can still occur under boost. Afterall, vortices are just turbulence, and turbulence can happen regardless of air density. In fact, the MAF very carefully creates calculable vortices by making a bit of turbulence in relatively smooth flowing air (thanks to the honeycombs for creating a nice laminar flow). The reason why these MAFs can't be used in a blow-through set up has to do with how the sensor measures the vortex frequency.

Basically, there are a few ways to measure the vortices... you can have the turbulent air collide with a mirror, which alternatively reflects a light beam on and off, creating a square wave proportional to air flow. Many Toyotas/Lexuses came with MAFs like this.

You can also have a pressure sensor directly measure the frequencies of the vortex, which is exactly how Mitsubishi chose how to construct their MAF sensor. A portion of the created vortices are diverted to a pressure sensor which similarly creates a square wave proportional to air flow.

The reason why this won't work post-turbo should be clear by now. By having the air pressurized, you're throwing in another variable that the MAF isn't capable of compensating for. The MAF probably wouldn't even work at all because the pressurized air would force the sensor to send out a continuously high signal, which just wouldn't make sense to the ECU.

 

[xveganxcowboyx]

So would a toyota/mirror style work in blow through mode since it does not use pressure in it's calculations?

 

[mavisky]

I don't know the answer, but something tells me that getting a lexus/toyota maf to work in our cars by yourself is going to cost more than the proven maft setup.

 

[Quasimondo]

There's also the problem of the MAS having a barometer and intake temperature sensor built into the unit, which would make for a real confusing situation for the ecu whenever there's a change in manifold pressure, or if you have an intercooler that's prone to heat soak.

 

[xveganxcowboyx]

I don't know the answer, but something tells me that getting a lexus/toyota maf to work in our cars by yourself is going to cost more than the proven maft setup.

Ah, I didn't mean in our cars necessarily. Just curious in general. I run a GM MAF and it works great.

And Quasimondo, do you think it would just be an issue of processing speed/reaction time for the ecu with barometric pressure or would it just be way outside of the ecu's abilities?

Again, just curious. Not planning on trying to make any of this work...

 

[Quasimondo]

It would alter the fuel & timing maps. High IAT's make the ECU pull it's global timing map to help stave off detonation. Baro readings help the ecu determine how much air it sees when it looks at the karman readings. Every time you move the throttle, because of where that MAS is, it'll alter how the ecu uses it's fuel and timing map.

 

[xveganxcowboyx]

Gotcha. Hot wire style MAFs FTW!

Thanks for indulging my curiosity.

 

[VelocitàPaola]

I think the mirror style MAFs might work in a blow through setup... you'd just need to incorporate an external IAT and MAP sensor with an appropriate translator. Like Kyle said, though, it'd probably end up costing much more than the proven GM MAF/MAF-T setup.