Cheap alternative to Z32 Airflow upgrade???

[R32-GTS]

Now correct me if im wrong but rb20det , rb25det and z32 afm are all the same size afm's at 80mm's.

This 10mm difference in size is not true at all.

[SLY33]

i think thats true from what ive read R32-GTS, but Tony seems to have a 70mm one on his 33! maybe not measuring correctly?

[T0nyGTSt]

Put this way... you cannot use the standard airbox if you want to run to a z32 meter.

The original r33 meter is smaller in overall dimesions if not pipe diameter.

T.

[Guest INASNT]

whats $300 in the big picture of modification!

dont be a tight ass!!

[Roy]

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This doesn't seem to make sense to me, NA cars still suck air, and how is two pipes going in to one (bypass and AFM) any different from two throttle bodies into one plenum? That works.

Yeh but with an NA car, any air going into the engine is seen by the AFM. What you are proposing is putting essentially a Y-piece after the AFM. Now air goes into the engine thru airfilter, thru AFM, then normally into turbo. Im guessing that if you have a y-piece, one end of which is open to atmosphere, then the air passing thru the afm can happily escape out your newly added bit of pipe. It will be seen as essentiall an inlet thract leak.

Also with twin throttle bodies, any air seen by the throttle bodies is still accounted for by the AFM. With the exception of the opening at the airfilter you require a totally sealed system to run the engine. Unless of course you want to use MAP, then hey what your saying will work fine as its all about pressure,

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You miss the point, it's about experimenting, doing something new and/or different, and if it can be done for 1/10price why not spend that money on other things?

Hence my suggestion of buying an unwanted AFM off a larger displacement car, (a trip to the wreckers) and grab a multimeter and experiment, see if you can do something different but still worthwhile.

[Rowdyr32]

Sydneykid: Thanks for some good solid info on it all, i'd be pretty happy with 220 rwkw (for now) so i guess i needn't do anything about my AFM, altho i've heard a lot of people say they'll crap out much earlier (like 180+ rwkw).

[Cubes]

Generally that is where your injectors are at their 100% duty cycle (180rwkw). You will need a re-mapped ecu and increased fuel pressure to overcome this.

[Roy]

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Pick someones brains with knowledge about flow dynamics (so i'll have a chat to dad soon) and you should be able to work it out. And as i said before once you've mapped your ECU to it, all done!

The fluids side of what you are saying seems ok. A huge part of fluid mechanics is Control, and using a hot wire meter to measure flow to allow an ECU to control fuel and ignition, then only to not allow the meter to measure all the air, means you are only telling the ECU half the story.

Im guessing that IF you are able to tune around it, then the amount of dyno time to get right (especially idle) would soon mean the whole process gets expensive quick.

Now that i have voiced my thoughts, what may work a little nicer is if you have say a butterfly valve on your added pipe piece that means at low throttle position, and low rpm remains closed meaning all air is accounted for by the AFM.

Then under full load the butterfly is opened allowing more air into the turbine to be compressed. Under full load and positive pressure downstream of the turbo i beleive there would be less tuning difficulties.

You could actuate a simple butterfly valve using some Hobbs pressure switches to signal when engine is one boost, and also a variable output sensor to detect throttle postion to allow the buterfly valve to creep to full open position dependent on throttle position.

Now this all assumes that your AFM cannot flow enough air for your hp requirements and is posing a restriction. And that you can talk to someone like your dad (you allude to the fact he is an engineer of some sort) to see of you can rig up control circuitry/sensors using bread board etc.

Then the purchase price of bits and pieces (pretty cheap really... but collectivley soon add up) and again a VH45 or Z32 AFM is looking pretty good.

[Sydneykid]

Hi Jordan, the problem with 1,000 bhp and AFM's is not with the max airflow. The issue is with reversion and tubulance from the big turbo/turbos and camshafts upsetting the AFM's at throttle close off and low rpm. You could use a smoothing device (HKS make them) that take the lumps out of the AFM readings, but for your purposes MAP sensor readings to the ECU would be better.

Let's face it a 1,000 bhp engine is not going to have a lot of idle, off idle and cruise quality anyway. So a MAP sensor is not going to be a big dissadvantage in that area.

Hope that helps.

[Warpspeed]

O/k guys, there seems to be some confusion here about how these things actually work.

The proper name for one of these devices is "a hot wire anemometer" and they measure air velocity.

There are actually two hot wires, but you can only see one. One is mounted near the middle of the moving air-stream, and a second one is mounted within the mounting stalk. The second hot-wire is immersed in the air-stream, but is located in still air.

An electric heating current flows through both wires, and this current heats both wires. Now as the wires become hot the electrical resistance of the wire changes.

If there is zero airflow, both wires will reach equal temperatures, and the voltages and currents in both wires will be identical. The electronics senses this, and outputs a zero flow signal voltage.

Because there are two wires, they will always be at the same temperature, even though the ambient temperature may vary very widely. That is why there two wires to cancel changes in ambient air temperature.

Now when there is air movement through the flow-meter, the wire in the air-stream cools down slightly, because the moving air carries away some heat. This causes the electrical resistance of the wires to be different (because one is now hotter than the other).

The electronics senses the difference, and feeds more heating current into the colder wire to force the temperatures back to being the same. The amount of extra power fed to the cooler wire (located in the moving air-stream) is the actual flow-meter output signal.

There is a very sensitive amplifier to detect even minute differences in the wire temperatures, so air velocities over a very wide range can rapidly bring the wire temperatures back to equilibrium.

Now if you place the hot wire anemometer in a tube of known cross sectional area, it becomes a flow-meter. A known flow will create a known flow velocity, which equates to a certain signal output voltage.

However an individual hot-wire flow-meter can be calibrated for any reasonable maximum flow range.

Now this is very important.

There is no real fixed relationship between flow-meter size and calibrated maximum flow. A 60mm diameter flow-meter could quite easily be set up to measure a higher maximum flow than a 100mm flow-meter, simply by changing the sensitivity of the electronics to the air VELOCITY.

So you cannot just say I am replacing my 60mm flow-meter with a 100mm flow-meter because it tops out in flow calibration.

A better approach in my opinion, is to remove the stalk and electronics from your existing flow-meter, and mount it in a tube of larger cross sectional area.

You will then know that the calibrated flow will have increased by the area change in the tube. Also the plug will still fit, and the connections be correct !

There are some pitfalls though. The hot-wire anemometer measures flow velocity at one point only in the airflow duct. That flow needs to be representative of flow across the whole cross section of the duct. It may not be, if there is a sharp bend or discontinuity upstream of the flow-meter.

Also the air can flutter (vortex shedding). This is the same effect that causes flags to wave in the breeze. The best way to fix it is to have a smooth straight pipe section upstream, and also to fit a wire mesh into the air-stream. It breaks up big vortexes into little vortexes and helps calm things down.

Sometimes the mesh can be removed without any obvious problem. Other times people that have tried it, end up having to replace the mesh. So take any pipework changes upstream of the flow-meter very seriously.

Another interesting characteristic of these things, is that they are sensitive to air density. At high altitude where the air is thinner, less heat will be removed by the flowing air from the hot wire. So the flow-meter automatically shows less airflow when the air is thinner. A useful characteristic.

I have not actually tried it, but it should be fairly easy to make a larger flowmeter body out of PVC pipe or something, and simply fit your existing hotwire internals. If it does not work, you can always put it back together again. The cost would be zero, and you can make it as big as you think you need !

[Roy]

Some early Nissan AFM actaully have a screw near the plug on the side for voltage adjustment.

Apparently this screw can be used to adjust the output of the meter, hence the signal.

[DAMQIK GTS-T]

Food for thought!

this would also require a re tune but here it go's

placing somthing (Small) in the path of the hot wire airflow path would slow the cooling affect of the hot wire therefore would change the band of resloution (would require more air passing it to cool to get to its 5volts max)

is this not why a stock car runs slightly richer when the mesh screen are removed from the AFM.

Damqik

[Rowdyr32]

Warpspeed you're a legend, thanks for all the info. The idea of changing pipe housing had crossed my mind earlier but for now i'd rather leave my original AFM just that, original. If i get another one in not so good condition i'd try it for sure.

Since looking on the net, like here (those vortex ones seem interesting), and discovering a bit more about how hey work, i've come to think that fiddling with electronics wold be a more elegant solution.

What do you reckon about the ease of altering the thermistors to ones with a different gradient?

Edit: Speeling

[Warpspeed]

I would be very cautious about doing anything with the electronics. The relationship between the two hot-wires (or hot-wire plus thermistor) is critical.

It would be very easy to really upset the zero flow calibration point, and also make the flowmeter highly dependant on ambient temperature. This would be a disaster. While the design looks simple, it is something that has been developed with a great deal of care and testing for mass production (at minimal cost).

Much safer to leave it completely stock and simply increase the airflow path cross sectional slightly.

I would also be worried about putting anything upstream in the airflow path that might cause cause wake turbulence. The hot-wire is a very fine wire that responds rapidly to air velocity changes. If the air is turbulent, the flowmeter output signal will be up, down, and all over the place. The EFI computer will probably freak out.

You must have a smooth airflow, to get a smooth flowmeter output signal. It is absolutely vital.

[Mr. En One]

Doesnt www.uniqueautosports.com sell 100mm AFMs?