Rx7TyreBurna

iTrader: (1)

Sorry if this is a duplicate... first time didn't seem to go through.

So, my MAF kinda sux. I was looking at another FC engine, and his AFS looked like it was round, as opposed to mine, which is kinda square. Is there any advantage to the rounder one? What would I need to do to make the round one work in mine. Any info or links would be great. Thanks.

sar

iTrader: (1)

Thr round one is s5s while the square flap is s4s. I don't believe that the air flow meters are interchangable (s4 has a much larger plug for the ecu than s5), but I suppose you could possibly rewire it as long as the resistances etc are within spec.

The advantages of the round moving cone one are that it has less resistance than the flapper door and can be oriented in any position. The s4 flapper door has to be mounted so that the hinge is on the side and not on the top or bottom (it will read wrong thanks to gravity)

You could just get a microtech/ haltech and run off of just your pressure sensor.

Evil Aviator

There is no advantage in changing the AFM from the square to round, and it would just be a waste of time and money. If you want something better, then get a standalone EMS installed and tuned from your local rotary engine shop.

BTW, the square MAF doesn't exactly suck, but the computer does.

Rx7TyreBurna

iTrader: (1)

Alright. Hehe. Save a little money then... hehe. Thanks.

NZConvertible

No it doesn't.

As above, there's no performance advantage. Even the orientation thing isn't that big a deal. Getting the S4 AFM to sit level isn't hard.

BlaCkPlaGUE

Yes but it is easiest not worrying about that and using the S5 afm. Personally I want to do this, just becuase of that, and if things finally go well with my car and I can get finished with this turbo project.

There is a disadvantage though, something about fuel cut.. I can't remember.

Ottoman

is it possible to "convert" to diff higher flowing AFM's?

do any non rotary AFM's work wit the engine? i think my maf might be dead of dying...(and there's no local spares)

like on the SR20 u can put the Z32 maf... on the 4G63 they convert to ls1 maf blow through style...

anything like that for our rotaries?

NZConvertible

I've just made a new TID and had no probs getting the S4 AFM to sit completely upright. I don't get the big deal.

Your fuel pump will continue to run after a crash, pumping fuel out of any broken fuel lines and potentially burning you to death...

I can't test them back to back, but the fact that the S5 AFM has an inlet more than 10% smaller than the S4's is enough to have me believe this swap is possibly a step backwards in flow...

BlaCkPlaGUE

I dunno, but why would mazda change the old afm for something different? If its more restricting then maybe they did it for better fuel economy? Or if its the same, maybe they changed it becuase of manufacturing costs?

Thats interesting though, so im guessing if the flapper door is shut on the afm, then the fuel pump turns off? How else does it know that the car is in an accident?
At idle, the flapper is closed and air bypasses through the restrictor screw area thingy, so if the fuel pump goes off when the door is shut, then how can the car run?
so confused....

SonicRaT

iTrader: (6)

The flapper isn't fully closed at idle, that's why it doesn't die. S5's use the ECU to control the fuel pump relay, where-as s4's used the switch in the AFM to control it, but NZ's right. what do you thinks less restrictive, a square path with no obstructions? Or ar ound hole with a 2" cone sitting in the center of the thing that you have to flow around/etc?

BlaCkPlaGUE

I don't know. No one knows for certain. We all don't know, becuase no one has any way of accuratley testing the afm theory.
I only said that I'd use it becuase its easier to use with a turbo setup in my honest opinion.

So your saying that if I pull the afm flapper closed at idle, that my car will die?

NZConvertible

Bingo! The plastic AFM's are cheaper than the old aluminium ones, plus the sliding cone apparently gives a more linear output. But since the S4 ECU is tuned for an AFM with a different output curve, this is possibly another disadvantage of the swap, since AFR's would be affected in an unknown manner.

In the S4, when the AFM flap is completely closed (which only happens when the engine has completely stopped), it opens a small switch which turns off the fuel pump circuit opening relay, killing the pump. In the S5, the ECU operates the circuit opening relay instead, and will switch it off if there's no engine speed signal from the CAS, i.e. the engine isn't turning.

There idea is that after a car crash the engine will almost always have stalled and the ignition will probably still be switched on and live. This means the fuel pump will continue to operate without some means of stopping it, hence the two methods above. If a fuel line broke during an accident, and the pump was still operating, a large quantity of fuel would be pumped out around the car, greatly increasing the chance of a fire.

If you use a S5 AFM (which doesn't have the zero-airflow switch) on a S4, you need to jumper the switch's wires to make the pump run at all, meaning the pump will run any time the ignition is on.

NZConvertible

Not true, all you need is both AFM's and a DIY water manometer and you can quite easily take very accurate measurements of how restrictive they both are. All we need is a volunteer.

Ottoman

could someone comment on this pls?

Aaron Cake

iTrader: (1)

What's interesting is that I actually experienced this, which is why I never recommend that anyone drive around with the "fuel pump test" jumper intalled.

In the summer of 2001, I was rear ended. The other car hit me at around 40 KM/H, pushing the rear of my car several inches while the front stayed stationary. I ended up stalling the engine, but leaving the key in the IGN position. The impact also cracked the fuel return line. So if that little switch in the AFM didn't shut the fuel pump off, the car would have been dumping fuel onto the ground for several minutes. Directly above the hot exhaust.

So don't take NZ's advice lightly. This kind of thing can and DOES happen.

Aaron Cake

iTrader: (1)

Sure, you could probably find an AFM on another car that would work. But why would you want to? The stock AFM is good to 400HP or so, and LONG before that level you should have moved to a standalone.

Ottoman

Cuz the new one is a fortune.. and mine MIGHT be malfunctioning, but i'm not sure I still have more detective work to do


btw how hard was it to fix ur car, I just had a similar experience with my other car and posted about it in the General section... i'm debating wheter it's fixable or a write off...


I noticed u live in London...

I lived there for ages... went to UWO and all, a regular at Jim Bobs and club Phoenix and all.. never saw a FC when I was there tho... wicked!

BlaCkPlaGUE

Hey I'd be willing to rig up a water test for the afms. Someone send me a junked but mechanically functional s4 and s5 afm.

I was thinking get one of those water cooler jugs on a stand, use some rad hose from a hardware store and a valve and clamp it to the afm inlet. Cut a hole in the top of the water jug, release the valve and time it with your watch. How fast the water drains to empty between the two will determin a winner.

anyone here with both afms, a day off and about 30$ to spend want to do this, so we can all know exactly what the hell is what when this discussion keeps on popping up?
If someone does this, we better post it in the faq

NZConvertible

That will tell you nothing. Short of a flow bench, measuring the vacuum in the duct immediately after the AFM with the engine under load is the only way to get meaningful results. You can do that for well under $30.

BlaCkPlaGUE

So how the hell do you do that?

NZConvertible

By making a water manometer like this:



The height the water gets sucked up the tube is directly proportional to the vacuum (or pressure drop) in the duct at the point you tapped into. This device is where you get pressure units like inH2O, inHg, mmHg, etc. If the water gets sucked up 10 inches, then you have a vacuum of "10 inches of water" (10inH20), equivalent to 0.36psi. It's extremely accurate.

Alternatively you can pick up Dwyer Magnihelic gauges surprisingly cheap on eBay, which are capable of measuring very low pressures accurately.

Aaron Cake

iTrader: (1)

Used AFMs are a dime a dozen from these cars. I often sell them for $25 Canadian.

The body shop I use is very experienced. They had to put the car in a frame jig and stretch it back out, and then weld in new rear quarters. NOT CHEAP, especially with my paint. But it was covered by insurance.

Cool. Club Phoenix is new, so you must have just moved away. London is a great place.. There are a few RX-7s around, but when mine is on the roard, mostly you see me since I drive constantly (on site computer service).

HAILERS

Have fun bippity bopping down the road sloshing fluid around using that rig. humor

Go Magnihelic. Then again, here in the upper hemisphere, we spell it Magnehelic, so you might get better results if doing a web search to sub the E in lieu of the I stated in the other post. Seems spelling isn't your strong point (humor)

Not only do *words have meaning*, but the arrangement of the letters in the words, have meaning also. (more humor, please)

By the way, seems I've seen that diagram you posted before. Somewhere in a online mag called Auto....D.

Just in case, it's issue 318 or AutoSpeed that has the article on bypassing air around the afm. Here.. http://www.autospeed.com/cms/A_2424/article.html

Ottoman

$25! nice.. i'll have to look u nag u more for parts when I need them :P


the frame jig is custom made to each car? how do they know the demensions to "stretch" it out to? can u elborate a litte?

daily driving the rexy allover proves it's robustness (i'm an IT as well.. but more server side, but did my share of tech support, (used to work telephone tech support Downtown at GTN that sucked.. I feel ur pain dealing with n00bs)

slvr7

iTrader: (1)

Interestingly enough, I have a couple AFM's on a home made test stand right now........
I'm comparing the outputs of an S4 & S5 AFM's at the same airflow level to see how 'swappable' they are.
I've got them both mounted on one end of a plastic pail (plenum), with a vacuum cleaner (actually two!) providing flow pulling air from the other end of the pail.
The AFM's are fed a ref voltage signal (4.7 volts), and I measure the Vsignal output with two multimeters. I alternately block the intake of one AFM while recording the voltage from the other.
So far, I've found that at rest (closed), and pushed wide open they return the same V to the ECU (3.7 and .38 volts, respectively).
At high airflow levels, returning voltages of under 1.5 volts, they return essentially identical values, within a tenth of a volt.
At low air flow levels, I'm having trouble getting results. The spring in the S5 meter seems stiff enough to prevent the cone from sliding away from rest position until the airflow is fairly strong. The FSM says at idle, it should be outputting 2.5 - 3.5 V, but when I get the S4 meter in that range, the S5 doesn't budge from 'closed'. However, it might be a problem with how I 'bleed' the suction to reduce the flow.
Other comments:
Air definitely has a much smoother, less turbulent path through the S5 AFM - the smaller input is probably offset by less drag on the air.
S4 flapper 'flutters' at lower airspeed - probably one reason for the revised meter design of the S5.

I'll post more results whenever I get some time.