Lex/stock turbo AFM blow through mod?

[siman]

Hey guys,

I was pondering this last week.
I was designing my piping for my I/C kit....when I had a thought.

Why cant we relocate our AFM's for those of us that do not really like looking at them?

I am prepared to get "flamed" on this...but serioulsy?

Can the/our Karman type AFM be a blow through design?

I know its a Nissan and a heated type MAS ( mass airflow sensor) but a couple of buddies of mine and online as well have relocated their MAS after th intercooler and before the intake manifold.

NOTE: I have a FFIM ( forward facing intake manifold) so you OBVIOUSLY cannot do this with the stock type intake piping!!!!

IS THERE ANY reason for this not to MECHANICALLY work with/for the Karman type AFM?

What/How does the Karman AFM meter air? Is it SPEED ( not speed density MAP) or Heat? What is it exactly? I would like to know that too!

thanks so much,

Jonathan mann

 

[IJ.]

Thought you were going standalone?

 

[siman]

like this:

Grey: I/C
White: Piping
Red: Turbo
Orange: Intake Manifold ( Forward facing style)
Yellow: Motor ( 7mgte :naughty: )
Blue: AFM ( Lexus or Stock...)

 

[siman]

Thought you were going standalone?

Well, further investigation into the Megasquirt ECU ( standalone map sensor etc..) seemed to be the cheapo way....but it has consequinces....constant tuning is needed since the car would run different every day. I know this first hand by my friends AWD GSX eclipse ( FTO) Mitsubishi....it runs 10.7 1/4 mile all day long....but its needing constant attention every time he starts it !!! Its mega squirt equpied and tuned right! But its just the computer is SO sensitive to every detail...

I cant deal with that.

Stand alone is in the future for SURE! But money right now and time that I have to spend on the car is limited. School coming up again and working full time and the supra being the daily driver....well you get my point IJ.

Its sad...but if I had it my way, and AEM EMS would be in the car right now!:biglaugh:

Either way I can make gagnormous amounts of power from the stock ecu with my SAFC II and a boost controller and wideband.


But IJ, you have any clue as to IF I could possibly do this mod to the supra?

-Jonathan

 

[chevyeater]

No blow thru with a Karmann sensor, sorry. Reason bieng that pressure is accounted for seperately from the AFM.

 

[IJ.]

I'd look into an MAFT/Pro if you're set on a blow through and getting rid of the AFM Jon.
(If you're on a budget and intend to go full standalone later surely you can cope with a little ugliness for now and keep the AFM maybe upgrading to a Lex?)

 

[siman]

No blow thru with a Karmann sensor, sorry. Reason bieng that pressure is accounted for seperately from the AFM.

Explain a little more....that is confusing...

I thought the AFM ( Karman(n)) did all the pressure reading/metering?

I had a feeling it would not work....talked to a supra guru buddy today but just wanted to check with you guys to see if you all thought of this back in the day or something LOL.

IJ: I already have a Lex AFM ready to go. I just modified my stock AFM (backed the screw ou) and had no ( ZERO) fuel cut at even 15lbs !!!)....but when I get my turbo stuff on I will have 650CC injectors ( maybe even bigger for insurance and later expansion on the turbo/fuel system side) and the LEX in accord with my SAFC/PLX wideband and boost controller....

 

[chevyeater]

Nah, the HAC sensor does the pressure reading. It is either in the ECU or near the glovebox depending on what year your car is. The Karmann sensor is basically providing measurements in CFM, not mass. The seperate pressure reading would become a significant factor if the air flowing thru the KV is very far from atmospheric pressure.

I like your diagram above though, lol.

 

[IJ.]

I like your diagram above though, lol.

LOL Ditto I think AutoCad have competition

 

[siman]

Nah, the HAC sensor does the pressure reading. It is either in the ECU or near the glovebox depending on what year your car is. The Karmann sensor is basically providing measurements in CFM, not mass. The seperate pressure reading would become a significant factor if the air flowing thru the KV is very far from atmospheric pressure.

I like your diagram above though, lol.

I know the air from the stock position is being SUCKED into the engine....

where as my design it would be blown through ( hence the name)....

Is this the problem? If so....could I just litterally put the afm in backwards so it acts as though the boost is vacuum? LOL......

as I see it, either way it looks like I am stuck with the stock mounting area....ugh.:icon_conf

GM MAF here i come!

oh and yes, I spent hours profecting the layout of that design in the very reputable Microsoft Paint 2.0 edition.....I have trained on that software since 1993!

:biglaugh:

-Jonathan

 

[siman]

anyone?

Why will it not work backwards then?:icon_conf LMAO

-Jonathan

PS: that is really a serious question...but you must add my laughter as in I know it probably will NOT work...but what the hey.....explain WHY and HOW the karman will not work that way if you know !!!

 

[gixxer750]

basically, the screen in the afm straightens the airflow for reading. It reads the frequency of the incoming air. When you pressurize the air, it screws with the frequency the air creates at certain speeds, making the AFM inaccurate

 

[GrimJack]

Let me explain.

The AFM in our cars will only work at regular atmosphere pressures - and only in conjuction with a pressure sensor. This is why you cannot put it in blow through mode, it cannot get an accurate reading if you are putting it post turbo in the compressed section of the intake tract.

Running it backwards wouldn't help, the AFM is a one-way device. Incoming air is straightened by a screen, then run past an obstruction to cause vortexes to form, then a very sensitive (and very fragile) sensor measures how fast those vortexes are circulating. The faster the air is rushing by, the faster these vortexes will be.

The ECU take the input from the AFM telling it how fast air is travelling in the sensor, combines that with the current pressure, and figures out how much air is actually entering the engine.

In order to switch to a blow through system, you would need to switch to a different type of air metering, either MAF via a MAFT, MAP via the MAFT Pro, or whatever system the HKS VPC used, damnifIcanremember what it was off the top of my head, and I don't suggest anyone go that route anyhow, with the nice cheap price a MAFT can be had for.

 

[Nick M]

The Karmann sensor is basically providing measurements in CFM, not mass.

Exactly right. It is a volume airflow meter.

What/How does the Karman AFM meter air? Is it SPEED ( not speed density MAP) or Heat? What is it exactly? I would like to know that too

Think of a boat going through the water. The waves moving out from the sides act the same as the air in the meter as it passes over the vortex generator.

then a very sensitive (and very fragile) sensor measures how fast those vortexes are circulating

Yes. By vibrating. The more volume the faster the vibration, which is translated to be frequency.

Now you have all the pieces to your question. Why not try the MAF-T. Many here seem to use it with great success at a low price?

 

[Supraholic]

The proposed configuration will under-predict air rate by ~30 % at 7 psi boost.

 

[Dirgle]

To put it simply the AFM only measures the rate that the air is passing through it. But it doesn’t measure density (pressure in our case), that is left up to a separate sensor.

So let’s say for argument that you have air moving at 1mph through the AFM.
You do it twice, once with the pressure at 14.7psi (atmospheric.) and again at 20.7psi (6psi on your boost gauge) The AFM will still read the same amount of air is passing through it both times, 1mph at what ever pressure the other sensor says. Obviously this would be destructive to you engine to run 20.7psi at 1mph, when it thinks that it's only moving 14.7psi at 1mph.

 

[Jeff Lange]

What if you relocated the pressure sensor into a pressurized section of tubing to get the pressure sensor, or possible calibrated a MAP sensor to output the correct signal to the ECU, instead of using the HAC as an atmosphere pressure sensor?

Just wondering, heh.

 

[Dirgle]

I've wondered this as well. But I think the ECU might have a few questions when it sees 15psi above atmospheric pressure.

ECU- "I'm reading a lot of airflow, what’s the pressure HAC?"

HAC- "26.7psi"

ECU- "WTF mate?!?! Where is this guy driving???... the bottom of the ocean?!?"

 

[GrimJack]

I get the suspicion that you would overflow the pressure sensor input register in the ECU. The design teams for these things usually build in +/- 25% for the operating range, and then another 25% in case something goes wrong, but past that it's the land of diminishing returns.

 

[p5150]

Nah, the HAC sensor does the pressure reading. It is either in the ECU or near the glovebox depending on what year your car is. The Karmann sensor is basically providing measurements in CFM, not mass. The seperate pressure reading would become a significant factor if the air flowing thru the KV is very far from atmospheric pressure.

I like your diagram above though, lol.

I would like to see what happens if you mount the HAC inside the intercooler or wired up a pressure sensor with a similar output.