Performance AFM

[TomoHawk]

I'm surprised nobody mentioned the 240SX AFM unit. It's got a bigger throat and you can get dadapters in clear plexiglass from Pallnet. It's a documented install.

thx

[PrOxLaMuS©]

AFM - Air Flow Meter > Flap type air measurement (older Z cars) found along the air stream before the throttle body, very restrictive, rather in-accurate.

MAF - Mass Air Flow > a little probe with a heated wire which is along the air stream before it reaches the throttle body, very unrestrictive. The Z32 and Z31 300ZX's have these MAF setups. Also BMW has Bosch MAF and AFM... many convert their BMW's from AFM to MAF

MAP - Absolute Manifold pressure? > Sensor which monitors the air pressure, and attached to the intake manifold after the throttle body, commonly found on turbocharged and supercharged engines, since it monitors the actual air pressure before it enters the combustion chamber. The MAF and AFM monitors the air before the air is compressed by the turbo or supercharger, and before it hits the throttle plate and enters the intake manifold.

The BEST type of air measurement is an MAF for an N/A car.. and an MAP for a forced induction car.

[thehelix112]

`Best'? Surely that depends on the design requirements does it not? I'd love to hear why you think a MAF is good for a NA car, and if it is, why its not good for a FI car.

Dave

[sblake01]

I think by 'N/A' he means FI as opposed to turbocharged. I think that MAF and MAP are fine for the engines they ere designed for. But to put that technology on a 30+ year old engine. . . well you won't have the variable valve timing, the direct ignition, individual coil packs, etc. and all of the other goodies that go with the more modern setups. The old EFI system, good or bad, is what it is. The more you change on it, the more a troubleshooting nightmare it becomes. I'm content to live with the AFM etc. on my 1970s vintage cars. JMO.

[hls30.com]

Stephen,

You are right about changing things and making them more difficult to troubleshoot,

but, I am doing my conversion to add tunability, and more important, the ability to go to ANY parts store and get components-try getting the AFM or any of the parts for a 75-83 efi system at a national parts store-much less a Mom and Pop! None of the parts stores in my area cary any of it in stock except the injector seals. Now add the cost factor in...Early EFI parts are expensive. The GM counterparts are not!

By taking the time to make this conversion, I will have made the car massively more tuneable, cheeper to keep, and still looking pretty stock.

I do aggree, if you want all of the goodies, just go buy a wrecked Oldsmobile Bravada, and move the entire engine and management system-it is easier to move a complete complicated system than it is to swap parts. The Bravada engine has all of the new technology goodies, and has very nice power curves, and is a 6!

[sblake01]

That's all true but I have enough of the important parts, including one each new in box AFM and all the electrical goodies to keep my 280 and the 810 going for as long as I'll probably keep them. I would love to see a 240-280 or even an 810 properly converted over to a VG30DE or even a VQ35DE with all the attending pieces. It would be sweet but then there's that price tag!

[PrOxLaMuS©]

Excellent information found from Pro Max Motorsports :

AFM - air-flow meters are the crudest form of sensing devices. It uses a mechanical flapper barn-door that is physically pushed aside by the intake air stream. The volume of this air-flow then determines how much the door opens. The door then is mechanically attached to a variable-resistor assembly that then sends a variable-voltage signal to the computer that roughly correlates to the volume of air flowing past it. However, there are some disadvantages to this method:

* mechanical parts wear out - with age, the pivot on the door can bind, the spring loses tension, the resistor-array wears out.

* flapper door restricts air flow - this is kind of like the Heisenberg-principle of air-flow measurement, where you can't measure something without interfering with it. The spring-loaded door actually contributes to turbo-lag because at low-RPM, low-flow conditions, the door is almost completely closed. Then when you floor it, there's insufficient flow to fully open the door until more air volume is moving past it. But you can't get more air flowing without first getting more air into and out of the engine to build up boost-pressure, so it's a catch-22.

* Insufficient range for upgrades - the operating range of output voltages and the volume of air that corresponds to them are fixed by the physical dimensions of the AFM. If you turn up the boost or even get high-flowing modifications like an aftermarket turbo, there can actually be twice as much air flowing as a stock engine. What happens then is the AFM door will be fully wide-open by 4000rpm, and the output air-flow signal will be clipped (fixed) from then on. So the computer thinks air-flow isn't increasing, and puts out a fixed fuel-amount. However, the real air-flow really is increasing and the limited fuel will cause the car to run lean, detonate and blow up.

* Inaccurate air measurements - what really matters to the computer, is figuring exactly how many oxygen molecules has been ingested. But the number of molecules for any given volume of air changes depending upon altitude (pressure) and temperature. So additional air-temp. and altitude sensors are necessary to modify the air-flow signal received and compute an air-mass number. Which would then logically match up precisely with a corresponding fuel-mass/volume number for the injectors to meter. Which leads us to the next upgrade...

MAF - mass-air-flow sensors replaces the mechanical measurements of the AFM with an electronic version. MAF-sensors use active analogue electronics to measure current flow through a heated wire placed in the air-stream. As air flows past the heated wire, it cools the wire, with more air cooling the wire more. The circuit then pumps more current through the wire to keep its temperature constant, with more current required for more airflow. This current then drives an output voltage to the stock computer. One nice thing about the MAF-sensor over AFM is that air-temperature and pressure compensation is automatically included in the output signal. Denser/cooler air will cool the hot-wire more, and a higher voltage will reach the computer to indicate larger numbers of molecules flowing into the engine. As good as this is, MAF-sensors also brings along with it some of the same drawbacks as AFM-sensors and adds some new ones of its own:

* Insufficient range for upgrades - since there are physical dimensions to a MAF-sensor such as diameter and length of wire, the range of air-mass that it can measure is finite. A sensor that's roughly the same size as the stock AFM will measure roughly the same amount of air for the same output voltage ranges. Turning up the boost with a larger turbo will max out a MAF-sensor and it too will send out a clipped fixed signal to the computer. Going overboard to a sizus-maximus MAF-4 sensor to closely match your maximum air-flow with the maximum output-voltage ends up causing low-flow problems. You get an idle that is irregular, stumbles or dies completely. Or the mixture is so rich at idle, you'll never pass emissions; there are people who remove and re-install their MAF kits regularly just to pass emissions!

* No ignition-compensation for air-temperatures - while the MAF-sensor may include air-temperature compensation into its air-mass output to the computer, the issue of ignition control is not addressed. MAF kits typically simulate the air-temp signal line to the Motronic DME computer with a fixed voltage, thus fooling the computer into thinking that air-temps are always 60 or 70-degrees. However, the stock computer actually does quite a bit of ignition-timing modifications based upon ambient air-temperatures. In order to operate optimally at the highest levels of performance, ignition must be adjusted for the conditions as well.

* Inadequate fine-tuning controls - the output curve of a MAF sensor isn't quite exactly the same as an AFM for the same air-flow patterns. And upgraded cars with increased boost have air-flow patterns that are completely different than stock; typically less flow down low due to increased turbo lag, yet more flow up top. So a way of massaging the MAF-sensor's output is needed to 'fool' the stock computer into injecting an appropriate amount of fuel across the entire RPM-range and load-ranges is needed. Some MAF kits use custom chips to provide this correction. However, unless your car has exactly the same turbo, with exactly the same boost curve and exactly the same intake & exhaust, not to mention internal wear and tear as their model car, your air-fuel mixture most likely won't be ideal. Other MAF kits include a four-knob signal-massager that tries to encompass adjustments across all possible flow & load ranges. This is a valiant effort, but much too coarse to allow tuning a car for maximum performance. Which brings us to...

MAP - manifold-absolute-pressure (also known as speed-density) measurements combine simplicity in sensor design with the power of digital microprocessors to compute a simulated volume-air-flow signal that is sent to the stock computer. As shown in the following diagram, you can completely replace the entire stock AFM-sensor (or upgraded MAF-sensor) and their associated wiring with a simple vacuum hose. As far as the stock computer's concerned, it's seeing the signal from an actual stock Air-Flow-Meter. Thus the computer will inject the appropriate fuel-volume to produce the highest power possible. This MAP-sensor upgrade kit doesn't suffer from any of the drawbacks of AFM- or MAF-sensors and has some unique benefits as well:

* No mechanical parts to wear out - this provides the best durability and longevity possible. Even MAF-sensors can suffer from contamination of its hot-wire (due to turbo-oil blow-by).

* Air-temperature based ignition control - an air-temp sensor is included that plugs into the stock AFM harness to provide computer with an accurate measurement of ambient temperatures.

* No flow-limits - since it is programmable, the AFM-Link unit will always linearly scale its output signal to fall within the 0-5V output range of the stock air-flow-meter regardless of whether it's installed in a bone-stock 951 with K26/6 turbo @ 12psi boost, or on a track-monster with K45/19 @ 57psi.

* Extremely fine adjustability - using non-volatile RAM memory to store all of its settings, this unit can be used to output ANY kind of an output air-flow map to ensure proper air-fuel ratios under all RPM and load-ranges (adjustments can be +/-127% in 500rpm increments).

Note that this isn't a piggyback-style signal-interceptor/massager like the Split-Second ARC-2, Apexi AFC, HKS AFR or the UNIchip. Those units sit in between the stock AFM or an aftermarket MAF sensor, intercepts and massages their outputs to fool the computer into thinking air-flow conditions are something other than what they really are, thus the computer is tricked into injecting less or more fuel to compensate.

The AFM-Link box (used in ProMAX MAP kits) is the actual sensor itself that generates (from scratch) an actual air-flow signal to the computer, rather than simply intercepting and massaging an existing signal from some other source.

Due to its advanced digital micro controller-based design, the AFM-Link fuel-computer is a fully self-contained unit that includes a MAP-sensor and the digital electronics to compute a simulated air-flow signal that closely matches ANY and ALL actual flow conditions. It can create non-linear discretely mapped fuel-curves to give you precise fuel-metering under all conditions.

[hls30.com]

That is a pretty good writeup, and even though it is written for selling Pro Max, does contain most of the reasons I chose the GM setup. Map, tunability, un-used channels for upgrades, data collection, cheep and readily available parts, COMPLETE technical manuals WITH excruciating and painful details, completely hacked, tuneableable in route, and more third party support than all of the other products combined.

My conversion is taking so long because of the time required for documentation. I am writing it all up to make it duplicateable, and as easy as possable to get great results in both the visual and actual use aspects.

Will

[thehelix112]

Pro,

Thats basically an advertisement for a MAP sensors, from a company that sells kits for them: low-and-behold! And you still haven't addressed why a MAF unit is ``best'' for a N/A car?

Dave

[PrOxLaMuS©]

well.. I am not 100% positive on my statement.. oops..

BUT... MAP sensors monitors the pressure changes in the intake manifold, and when you have a turbocharger or supercharger and you are shoving in 10 pounds of air into the engine, on top of the 14.7 standard atmosphere psi, it is important to monitor the actual pressure RIGHT before it enters the engine.

MAF setups like I mentioned earlier monitor the air wayy before it enters the intake manifold, and even BEFORE the turbo or supercharger compresses the air.

Obvisouly AFM setups have been done away with due to several reasons as listed in my last post, lots of mechanical moving parts, they can break, etc... and the FLAP blocks and restricts the air flow.

This is entirely my educated assumption, that if you can't go for an MAP which is by far the most accurate, the MAF would be ideal for an N/A motor, mainly due to these reasons. The MAF monitors "temperature" differences, as the air flow passes the little heated probe it changes the signal sent to the ECU.

Now as air becomes compressed, it naturally HEATS up, which is why we now use intercoolers to cool the charge.... this is why the MAF is placed BEFORE the turbocharger or supercharger.... since it would be rather inaccurate...

problem is, with an MAF on a turbo/super setup, is the air is measured BEFORE its compressed which means, as the air is compressed at 10 psi or could be 6 psi ... depending on your wastegate.. but the air measured before it is compressed.. so.. the MAF will not compensate for the increased boost. Don't forget, a charge at 6psi right after the turbo outlet, can change to 7psi to the throttle body with a good intercooler, that's an extra pound of air into the engine, that can't be compensated with fuel.

I say that the MAF is ideal for an N/A engine since it is in a direct flow between the air filter and the intake manifold and it measures the EXACT airflow RIGHT before it enters the engine. Not before air is compressed..

i'm not an expert.. just a few minutes of research and this is my conclusion.. if i am wrong or inaccurate please correct me!

[thehelix112]

Pro,

The MAF measures the air before it is compressed as you say because it is calibrated to measure the temperature difference based on uncompressed air. MAF sensors have no issues at all coping with forced induction applications provided that all the air going past the sensor is then ingested by the engine - be it compressor and heated, or uncompressed and cooler.

The only time you get issues is when the air goes elsewhere AFTER its gone past the MAF sensor (like a vent to atmo blow off valve).

Oh and there is no way the pressure of an inlet charge is going to increase after an intercooler. In fact it is gaurunteed to decrease, the intercooler (and all piping/etc etc) is a restriction in the flow and will hence cause a pressure drop. Or are you saying that your intercooler is a compressor? I think you are possibly talking about charge density? Which is entire different and relates to the MASS of air flowing in.. and what does a MAF measure again?

Dave

[PrOxLaMuS©]

hmm.. thanks Helix for clearing thing up for me!

Your right about the intercooler and pressure differences..

as a general rule I thumb.. as air cools it becomes denser... which made me conclude that as an intercooler "cools" the air, the air becomes much more denser.. i think I jumped to conclusions thinking that the increase in density increased the overall volume, which is wrong, same amount of air, just a diff density.