Mounted AFM AFTER turbo. Here's what I noticed
 

Well, I mounted my AFM right at the TB....
Before, I always had a little low end roughness when touching the throttle.. just a little misfiring, etc, but nothing bad.
Anyways, I figured it was probably from having the turbo and IC and all that im between the throttle plates and the AFM. I figured that it was going lean for a split second because the vacuum from the throttle plates opening took too long to reach the AFM.... Well, I was right!
MAN does it run smoothly now. No misfiring, perfectly smooth, instant throttle response! I LOVE it!
It also should theoretically give you a *little* bit more power, since the AFM represents less of a restriction after the turbo, but you HAVE to have an S-AFC or something, because it willl read leaner under boost. It also allows you to get rid of the TID all together, and open that airflow up a bit. I did it more of a drivability/smoothness mod, rather than pure power.

Anyways, bottom line- great mod, greatly impoved my response and drivability...I'd really recommend it if you have a big FMIC and such, just NEED to be able to compensate for the leaner reading and tune it under boost. There are a lot of big power 7's in Japan that have done this..... it's NOT a huge power gain (though I'm sure it is measurable) but it gets rid of clutter and really makes things smoother!

well, post some pics!!!!!!!!!!! :)

That's great. With an Safc you could tune out the air/fuel change that it would make and have less dead space between it and the plates.

Now if only there was a way to put the FMIC before the turbo . . .

seems interesting but since i have microtech i don't really care, but i know how it feels like without a TID/AFM though, boost sounds alot louder and hits earlier.

Did you relocate your air intake temp. sensor? If you didnt that may be what is causing the car to run lean. The air going into the engine after the turbo is much hotter than the air coming from before the turbo.

All you guys with flapper door AFM ('87 & 88 TII),
you cannot do this . The AFM *has* to go before the turbo. Why I know? I've done it when I installed my IC and had to re- do the piping. For one, the flapper door type AFM has to be level either ribbed side down or up but not angled in any way. Gravity will have an effect on the door. Another is the black cap will blow off or your boost will leak if you make a hole in it. You all see the Japan guys do this but they're all '89'91 AFMs. I'm not sure how much pressure it can handle though. The '87,88 sure cannot handle more than 7 or so psi.

:withstupi :peace: :D

I dont need no stinkin AFM.

Re: Mounted AFM AFTER turbo. Here's what I noticed
 

I don't believe this is correct. The fact the air is pressurised makes no difference. It's just as difficult to push air though the AFM as it is to pull it through. As we've already discussed, the mass airflow after the turbo must be exactly the same as before it, so the same effort required to move air through the same restriction should be the same no matter where it is. When someone shows me before and after dyno proof that this mod improves power, I'll happily stand corrected... ;)

I'm glad to here this mod was successful though. I can see how moving the AFM closer to the engine would allow the ECU to respond quicker to what's actually happening in the engine.
Have you made any adjustments via the S-AFC? How much was required? Where are the pics? :D

There's no need to. There's an air temp sensor built into the AFM (so that one's OK) and the ECU's main air temp sensor is still located downstream of the new AFM location (intake plenum on NA's, TB entry on Turbos).

Me either now!!!!:bling:

I hate arguing about this mod because it is a fact it does work! Air moving out of the turbo is moving slower than air moving into the turbo. It has to. In order to compress air, you have to slow it down. Although the air is moving slower through the afm now than it was before the turbo there is still the exact same amount of air flowing through it. The restiction does not look as big to the incoming air as it did before. The molecules are more compressed. If you shrink yourself and walk through a door, the door is suddenly bigger and there is more room. What's not to understand? I've endorsed this for years and I'm glad to see someone that did it and realizes that it is great. Ultimate power won't be affected since your turbo still flows the same amount of air but throttle response is much better and spoolup times are improved. How the hell is a dyno going to prove that? FWIW you can use the flapper door afm with no problems provided that you keep it level. I've seen this done many times.

so if us S4 guys cant use the flapper AFM can we get a S5 afm and work it like that?

You can use the flapper door style as long as it is mounted flat. What IWNTA20B is referring to as a problem is with the plastic cover that goes over the electronics in the afm. It is merely siliconed in. You will be OK as long as you can keep this attached and still sealed. If you want to change to the other afm you will have to swap a couple of wires. Someone did a writeup on the conversion but I don't know where it is.

Well in some ways bam is right. If you look at the basic equation for noble gases (all found in our air) which is PV=NRT. Pressure and volume are directly proportional. Therefore if you incress the pressure, you also incress the volume. So even though the restriction by the afm is the same, you will be moving "more" air through it in a pressurized form therefore reducing the restriction to every individual molecule of air. So puting the afm after the turbo will reduce the restriction to the air moving through it when you look at it from a molecular level.

Just to clarify, I neven said it wouldn't work. ;) Here you're saying it's less restictive... ...but here you say power isn't affected. It you're lessening a restriction in the intake path you should see an increase in power, just like fitting a pod filter for example. I know this mod will improve the AFM's response time, I just don't see this making noticable power improvments. Before and after dyno testing would show this either way. :)

You've got that backwards. If NRT remains constant, then PV must also remain constant. If P goes up, then V must come down to keep PV constant. Assuming T is kept constant (and it's not during rapid compression, far from it) then as pressure rises volume decreases. ;)

Hmmm, sounds tempting. Very tempting. I love whipcrack response time from engines. :whip:

I've seen this mod go back many years in the Japanese magazines. My question is how does the AFM handle the extra heat? Normally all it sees through it close to ambient air temps. But even with a decent FMIC, the air in it will be a good deal warmer than it used to deal with. Or does that not matter much because the stock location sees a decent amount of underhood temps from being located near the turbo but on the other side of the engine bay it'll be relatively cooler.

So, will the heat mess it up?

I'm not sure why I'm so concerned. I guess I like to see innovative and experimental minds at work. Soon I'll be going to a rather large hotwire MAF (closely related to a 300ZX but from a certain little RB engine ;) ). All I need to do is get the MAF from a buddy overseas that has an excess of them laying around and use the GReddy e-Manage to do the translating. There are those that say it's impossible. But they haven't seen it done yet. They will, oh yes, they will. Muhahahaha. :evilgrin:

It should handle the extra heat just fine within limits (it looks like it will top out around 65deg C though). The temp sensor in the AFM is used to compute the density of the air, "multiply" by the AFM vane reading and you get mass flow. So the ECU will just think its a really hot day out and the air is thinner (remember the PV=nRT). The temp sensor in the intake elbow is used for timing retard.

Henrik
87TII

I was thinking more along the lines of the durability of the unit.

The air temp sensor in the AFM is the one I was talking about. If the ECU gets a air temp reading thats hotter then the air before the turbo actually is, then the amount of air being read by the ECU is going to be less then it actually is. If the ECU thinks less air is going through the engine, then its going to give the engine less fuel, resulting in a lean condition. Remember, the ecu is programmed to assume that the air temp sensor is going to be reading a temp at or close to outside temp.

If anyone knows where the thread that talked about converting to an S5 AFM is, or where I can find a write up, I'd love to switch, I was always under the impression it just couldn't be done.

As far as whether low pressure, high volume air (before turbo) gets measured differently then high pressure, low volume air (after turbo) in theory they should be the same. What the flapper door is measuring is how many times it gets hit by a molecule of air each second (or millisecond) (O2 or N2 or whatever), and how hard the molecules hit. The more molecules, and the faster they're going, the further it swings back. Whether all those molecules are squeezed together, moving (relatively) slowly , or spaced out, but moving fast shouldn't matter.

Of course the real world screws up all this theory, but I have no idea how, or what effect it has, seems like it would be small though. I just think measuring the air closer to where it matters makes sense.

The air temp doesn't matter provided it remains within the correction abilities of the ECU (tops out at about 65deg C). The AFM measures flow and temp at a common point. Given the air pressure (from the ATP sensor) with the temp the ECU can calculate air density and with the measured air flow can then calculate the mass flow. The problem is that the ECU expects the AFM to be at one atm of pressure which it now is not when under boost and due to the physics of the AFM it will read lean under boost. This is what BamBam7 is using his AFC to correct for.

Henrik
87TII

It's easily done just by matching up the wires, but there's no point. The S5 AFM doesn't flow any more than the S4 one (the S5's is actually slightly smaller). It will also cause changes in mixtures due to the fact that the S5 AFM's output is more linear than the S4's, which is more exponential. I'm not sure if it'll get richer or leaner, but it will change. You also lose the fuel cut safety switch, which might save your life one day...

Ah I see - shouldn't be a problem as the electronics are not directly in the air stream. Besides you're only going to be on it for a few seconds at a time so the thermal mass of the meter will help as well.

Henrik
87TII