I wanted to switch to the the S5 if I put it after the turbo for a couple reasons, it doesn't have to be mounted level, and it can handle boost better then the S4.

How would I lose the fuel cut by switching? isn't that built in to the ECU?

And just so those of you who have not taken a physics lesson in a while know, it is more efficient to push than it is to pull. I realize that when you start pushin 8psi of air through the AFM, it is not really gonna make a difference, but like the thread starter stated, this mod is going to be for throttle response, driveability, and low rpm smoothness.

I'm not talking about the fuel cut from too much boost. There's a safety switch in the S4 AFM that cuts power to the fuel pump in an accident to stop fuel being pumped out of broken fuel lines and causing a fire. The S5 AFM doesn't have this switch, as this function is handled by the ECU instead. Personally this is not a feature I'd like to lose.

As mentioned above, the S4 AFM can be used in this location.

isnt the s4 afm square or sumthin? u gotta get that adapter thingy, an doesnt that make it more restrictive?

NZ, it *should* have a slight increase in power due to the turbo drawing in denser air, although slight. The turbo doesn't have to work as hard to reach the same amount of boost, which means a cooler intake charge. :)

The square opening of the S4 AFM is actually slightly bigger than the round opening of the S5 one. The adaptor makes no difference.

The density of the air entering the turbo is in no way affected by the AFM's location.

ok PV=NRT...the noble gases are Helium, Neon, Argon, Krypton, Xenon, and Radon. where do you live that these make up the air? also, that equation isn't the noble gas law...its the ideal gas law. the ideal gas law works to get a minimal idea of how things will behave...but gases are not ideal so you have big charts of ratios and constants to factor in to get the right numbers for gas behavior calculations. and like NZvert pointed out, your thinger idea was backwards :p:. just trying to point you in the right direction here heheh.

for the basic common sense explanation of this...all the air that the turbo blows has to be sucked through the afm. since imaginary air doesn't appear magically in the turbo, the same amount of air will flow into the turbo as out of it. air before the turbo will be cool low pressure and out of will be hot high pressure, but thanks to the air temp sensor, the ecu can correctly figure out how much air is actually flowing through the afm (by calculating density using the temp) as long as the sensor and afm are running the same temp.

so from this all...i can see throttle response going up maybe since this higher pressurized air might pass through the afm more uniformly, but performance should be relatively unchanged.

the moral of the story? throw away the afm which happens to be the smallest bottleneck in your intake system and get a standalone :D. now to dig up some money for the standalone...

I don't agree, just like there is a pressure drop with having an air filter, there is one from suction pulling the AFM door open, however slight.

Density will not be affected. You have the same density regardless of if there is an extra door there or not. If I take a door off of my house and relocated it I didn't affect the density of the air in those locations. Same thing here. There may be less air or a delay of incoming air but regardless it will still have the same density per volume.

what a stupid example. Is air moving through your house at 70+ mph? Have you ever thought about (or even calculated) how fast the air is moving through an RX-7's intake?

Let me remake your example into one that fits the context. Instead of having a wall, have a wind tunnel fan. Now crack your door open, but only let it open so much. Obviously a wind tunnel would be too big.

It's physics, have you had it? If simple things on an intake didn't matter, why would people port engines, or build harmonic intakes?

There IS a pressure drop from air filters, so why wouldn't the AFM create one?

We know there's a pressure drop through the AFM. All restrictions cause a pressure drop, in fact that's how they're measured. But you said there's be a drop in density, which is a completely different thing. The density does not change.

Yep you said density not pressure. I didn't say anything about pressure. Yes I've had physics, I, II, and fluid mechanics. You obviously haven't or you've forgotten everything.

yeah, I'm wrong, I was thinking pressure, not density. :)

Is there any concern about the AFM exploding after too much boost?

ok so whats the correction needed with the afm in the pressurized side of the intake....

sorry wrong thread.. tried to delete, but couldnt

A chunky piece of cast aluminium subjected to the relatively low pressures associated with turbos is not going to "explode". The worst that might happen is the sealant around the black plastic cap splits and causes a leak. I believe this is the main reason Japanese tuners often swap to S5 AFM's when locating the AFM post-turbo (not for more power).

That's cast aluminum? I coulda sworn it was plastic. The assumption was the only reason I asked about the afm exploding... Thanks

I second that since I've done it. *MOST* Fc you see in the Japanese mags are S5s. So, they can be mounted anywhere and angle has no effect. The S4 black plastic top will leak and ANY sealant you use will not work. In worst case, you'll crack the plastic from too much pressure. There is no gain by switching to S5 AFM so that's something I didn't experiment with.

I thought you were talking about the S4 AFM, which is aluminium. Even the S5's plastic one is going to take a lot of pressure. I doubt it would be a problem.

anybody got an update on this???

I was going to be attempting this shortly on my NA, mounting the AFM right next to the throttle body to see if I get any noticeable increase in throttle response. I was just looking around on Google for any info to see whether or not this messed with the intake velocity at the TB to any discernable degree, and was very surprised to find this thread pop up.

As a side note to the latter argument (I can't help myself), density IS in fact affected. Density and pressure aren't the same thing, but they often go hand in hand in the real world. For a fixed volume and quantity of air, increasing the temperature increases pressure but does not affect density, as the distance between molecules does not change, but the amount of force they exert upon each other increases as energy levels rise. In this case density and pressure are not related, but it's also a sealed system.

In the case of a system with airflow, a "restriction" will create a measurable pressure drop, as it impedes the flow of molecules. Imagine a subway terminal: on one side of the pinwheel people are backed up, packed together, and moving slowly. Past it, there is a "pressure drop", and in response the people are more free to move, walk faster, and -- most importantly -- the distance between each person increases, which represents a decrease in density.

The turbo provides pressure in the system, while the engine intake process relieves the pressure. The turbo, however, attempts to provide more air than the engine would naturally accept, so the quantity of air molecules confined to the space between the turbo and engine increases until a balance is reached, and the engine's fixed intake volume contains the same quantity of molecules as provided per unit of time as the turbo's flow rate. Any restriction along the way unbalances this process by creating an event other than the engine that affects flow rate. By resisting the rate of flow, the AFM creates a new, smaller flow rate against which the engine makes its balance. The number of molecules per unit of volume will have decreased -- a drop in density. As the distance between molecules increases, their overall kinetic force per square unit of area decreases, which is measured as a drop in pressure. Whew.

That was fun.

To agree with NZ, the mounting location of the AFM has no noticeable affect on power as initial restrictions are far less influential on turbo systems compared to NA systems. A restriction decreases the density of the air, and the turbo encounters less resistance and compensates by spinning faster. This creates a greater imbalance, in the end providing the same amount of boost by pulling air through the restriction at a higher velocity. If the filter can't take it, it gets sucked into the engine.

But to disagree, it definitely affects density, as I just explained. Pressure drop, same temperature, higher velocity, less density.

Err, ignore the indicated part. Temp would definitely drop. It's 3:20 AM and my brain doesn't working less good.

I can't comment on the power issue, but I found a noticeable decrease in spool time/amount of throttle need to spool when I moved my AFM post turbo in my eclipse. Of course DSM MAFs look a little more restrictive than the FC's, but I don't doubt it would help some.