Air Flow Meter "electronic" Modification?

[Antimatter]

I know there has be much talk about fitting air flow meters into larger diameter pipes etc - However I would be interested to know if there is a modification that can be done to the electronics of the AFM in order for it to see more airflow before it hits 5.1v. I know MINES sold modified RB26 AFM's... just wondering if it is something that could be cost effective for the home "electronics" hobbyist to attempt. Wanted to have a shot at the air flow meters on my GTR...

I know the Z32 / Nismo upgrade has proven to be reliable and effective - however I would love to hear some opinions on this more "invasive" approach?

Cheers

Steve

Edited October 18, 2006 by Antimatter

[[WLDCRD]]

pm sent

[chrissso]

This is one of those questions that no-one wants to answer 'cos no-one really knows enough about it. It's a hard question. There are alot of variables, aerodyamics and physics involved.

The Z32 is the same diameter as the RB25 MAF, but will detect a faster airflow than the max detectable airfolw of the RB25 MAF. his gives it a higher "resolution".

You cant get more resolution from the RB25 sensor, however, you may be able to bring the airspeed down so that the airflow through it is in it's readable range.

Something off the top of my head is to make the tube around the sensor bigger to slow the airspeed past the sensor down. You would need to cut the sensor out of the tube it's in and glue it into a larger one.

Another - put a difuser infront of the sensor. A problem wit this method is that there are a lot of variables that can change like occilating windspeeds caused by eddies that a difuser would make.

These both need to be tested on a bench.

A resistor wouldn't work, as it would just take from the resolution of the sensor.

Can't think of anything else...

[Antimatter]

Hey Chrissso

Thanks for your feedback - however my "very limited" understanding would make me think that buy decreasing the AFM resolution - you are in fact increasing its capacity to flow flow more air before it reaches peak voltage - I guess my question is would the modification be simple (ie a resistor somewhere in the electronics) or more complex (like replacing the hotwire element or substantial modifications to the circuit inside the AFM). Or perhaps somewhere in between...

please dont flame me to hard though - I really do only have just enough electronic knowledge to get me into trouble...

Cheers!

This is one of those questions that no-one wants to answer 'cos no-one really knows enough about it. It's a hard question. There are alot of variables, aerodyamics and physics involved.

The Z32 is the same diameter as the RB25 MAF, but will detect a faster airflow than the max detectable airfolw of the RB25 MAF. his gives it a higher "resolution".

You cant get more resolution from the RB25 sensor, however, you may be able to bring the airspeed down so that the airflow through it is in it's readable range.

Something off the top of my head is to make the tube around the sensor bigger to slow the airspeed past the sensor down. You would need to cut the sensor out of the tube it's in and glue it into a larger one.

Another - put a difuser infront of the sensor. A problem wit this method is that there are a lot of variables that can change like occilating windspeeds caused by eddies that a difuser would make.

These both need to be tested on a bench.

A resistor wouldn't work, as it would just take from the resolution of the sensor.

Can't think of anything else...

[mad082]

my understanding of putting a resistor in:

the problem with putting a resistor in is that the afm will still hit 5.1v, but the ecu will think it is lower. the voltage won't actually go any higher.

the only real way to do it is to make it so the hot wire doesn't have as much air pass by it, e.g. have a tube that lets air bypass the afm. to do this you would need to have an aftermarket ecu and to tune it on the dyno, and hope that the amount of air bypassing the afm is always the same as what you tuned it to be.

[R33S2]

what about a small hole drilled in the tube behind the sensor? that would slow the flow past the sensor and is reversible. You could also pipe it to a gate valve that can vary the flow.

[700HP-GTR33]

I have heard of tripping the afm ,higher Voltage.(Japan)

But the tuners in Australia do not want to work out all the figures to enter into the Ecu after they have done this...........all of them think it is a waste of time.

When you send a higher voltage through the unit the tables all change and each point needs to be re-mapped.

This is my understanding and why Z32's are so popular with tuners...easy put in and tune.

[mad082]

I have heard of tripping the afm ,higher Voltage

please explain

[700HP-GTR33]

The power that is pushed through the AFM is not 5.1V but by memory 5.7V but do not quote me on

the exact figure though could be 5.9V.

So then each figure on the air/flow map changes , by memory I was told that this ment

the AFM could read 1.4 times more air movement .

So then they would read the map previous, and work out the AF/ratios they need to enter on the new map.

Which ment each figure on the map had to be worked out and entered in to the ECU.

I am not sure how they actually increased the voltage though.

Just was told they did

[chrissso]

what about a small hole drilled in the tube behind the sensor? that would slow the flow past the sensor and is reversible. You could also pipe it to a gate valve that can vary the flow.

Essentially, this is diffusing the flow. Any tube or constriction is difusing the flow.

It might cause alot of turbulance. Need practical bench testing to see if voltage versus flow is stable and accurate everytime.

The tripping is something else I was thinking of, however, couldn't quite get my head around. It makes sense.

As with the remapping, the maths will have to be done for any method of increasing or redistributing the resolution of the MAF.

Resistor will not work. You can lower the voltage output, (or maybe even input to the maf) but the MAF will still only read a maximum amount of airfow.

We know that through a given size of tube, the airspeed will be constant for the volume of air constantly flowing through it.Therefore we either need to increase the resolution to read a higher airspeed, or decrease the airspeed per volume of air (bigger tube). Or possible slow the air around the sensor down. This may not work however due to turbulance, and the result maynot be a linial rereprisentation of the original graph (the later may not matter)

Thanks

[CEF11E]

all these things are well and good. and will work.. I have even tried using resistors and changing the diameter of an AFM and I can tell you neither are a viable solution...

Why?

The problem lies in the way the ECU reads and references the voltage. This is called a VQ map and is a 128 load point map in the ecu and is callibrated to the AFM.

Once you change the diameter of the afm or modify it the VQ map is no longer a true representation of what the AFM is doing.

BUT THAT IS WHAT WE ARE TRYING TO DO!!!! i hear you say. yes you are trying to get higher resolution at higher flow. bit what you are actually doing is feeding an unknown comodity into the ECU.

Both the PFC and remapped stock ECU have the ability to use SET VQ maps. eg: Z32 afm, Q45. these maps match the AFM you are using so the ECU knows exactly what is going in.

If you change thediameter of the AFM you no longer have a predictable callibration table to work with when tuning

[CEF11E]

And the last point is.

If you are changing the AFM you already have a modified car and another $300 for a Z32 or Q45 unit is peanuts. and is the best option ALLWAYS

[700HP-GTR33]

all these things are well and good. and will work.. I have even tried using resistors and changing the diameter of an AFM and I can tell you neither are a viable solution...

Why?

The problem lies in the way the ECU reads and references the voltage. This is called a VQ map and is a 128 load point map in the ecu and is callibrated to the AFM.

Once you change the diameter of the afm or modify it the VQ map is no longer a true representation of what the AFM is doing.

BUT THAT IS WHAT WE ARE TRYING TO DO!!!! i hear you say. yes you are trying to get higher resolution at higher flow. bit what you are actually doing is feeding an unknown comodity into the ECU.

Both the PFC and remapped stock ECU have the ability to use SET VQ maps. eg: Z32 afm, Q45. these maps match the AFM you are using so the ECU knows exactly what is going in.

If you change thediameter of the AFM you no longer have a predictable callibration table to work with when tuning

There is a formula to work out true values when this mod is done...its just that it involves work for tuners....so they opt. out.

If one tuner did the calibration after the higher voltage...this could be used in all the other cars after that.

We are the stupid ones that think by the Z32 and thats it.....especially for a gtr that needs TWO.

[Guilt-Toy]

Q45. thats the go.

[CEF11E]

There is a formula to work out true values when this mod is done...its just that it involves work for tuners....so they opt. out.

If one tuner did the calibration after the higher voltage...this could be used in all the other cars after that.

We are the stupid ones that think by the Z32 and thats it.....especially for a gtr that needs TWO.

100% true. but usually it is cheaper to buy a $300 unit than pay a tuner another couple of hours.

[Roy]

Well working automation...sensors are typically 0-5V and 4-20mA. I would be very surprised if they drive a signal mcuh past that range as it would ber very difficult to integrate into the hardware, Sure the code and software may be fine, but the hardware may not like the higher voltages. ????

An AFM upgrade is pretty cheap and simple. I understand its cool to tinker, but engien tune is one thing i would not suggest you tinker with. Tune is the end all be all of your car

[R33S2]

This is what made me decide to go MAP sensor, plus being hardier than a MAF sensor.

[GTR-Ben]

Well they must do something special in Japan as i have seen some funny things done.

E.G 800HP GTR with stock twin 2 1/2" Air Flow Meters, chipped ECU.

another 700HP GTR with a single 3" Air Flow Meter probe plumbed in after the intercooler.. Single..

So there must be something you can do to change the resolution of the AFMs. Must be some big secret.

[Roy]

I think it has less to do with the AFM and more to do with the fact that they shove the lambda up the bum, and tune for WOT off that. ?????

Also, isnt there something in the PFC software that allows you to change the range/scale of load points ???? Is that somehow related???

[Antimatter]

I know I am at 5.1v at about 5000rpm on my GTR - tune becomes 2 dimensionsal after that....

Seems to work ok as my AFR still hovers around 12 all the way to rev limit and driveability is very good... I am just looking for an "outside the box" approach to giving the air flow meters more capacity...

I am really grateful for everyones opinion!

I think it has less to do with the AFM and more to do with the fact that they shove the lambda up the bum, and tune for WOT off that. ?????

Also, isnt there something in the PFC software that allows you to change the range/scale of load points ???? Is that somehow related???