NZConvertible

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.

mr_vaughn

iTrader: (1)

anybody got an update on this???

Delphince

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.

Delphince

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

twilight slide

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.

NZConvertible

IMO that would be a real waste of time. The AFM on an NA is already a lot closer to the engine than on a Turbo, so moving it any closer has very little potential for improvement. But you will be placing the AFM directly over the exhaust, which is not a smart place to put it.

Since the TB's cross-sectional area is fixed, the only thing that can effect velocity is airflow. Velocity at the TB will only be affected if you stick something in front of it that affects airflow. Relocating the AFM is very unlikely to do that since it's already in the system.

Delphince

Yeah, I don't expect to notice much, if anything. I just figured it was worth noticing if there was any change in throttle response by having it closer; I don't expect any change in power, torque, or top end.

I'm using "velocity" in the sense that that is referred to when people speak of the air building momentum to assist in low-end torque -- the advantage of long runners over short runners and such. I was worried if I put an obstruction like the AFM too close to the engine it would start to interfere since there seems to be some line of thinking engineers use that causes them to almost always put the AFM/MAF as close to the start of the line as possible.

At any rate, the reason for it all is I've been building an entirely new intake snorkle from the TB forward so I can properly locate and box a cold air intake and get the nice tone of an all-metal intake to go with the new SP2 exhaust. I figured it would be worth messing with a couple things while I'm at it.

joeylyrech

iTrader: (11)

I am running a S5 T2 flow meter on my S4 t2 car,i placed the flow meter at 12 inches off the TB plates(third gen upper and tb) plus tuned the flow meter with the e-manage and it runs great,i didnt have a problem with my AFR at all but im running 1000.cc secondaries 550 primaries on pararel fuel system on a HYBRID TO4E,now before the change i was running a vented BOV and the car uses to backfired now with the BOV right at the turbo it wont backfire anymore,I am very pleased with the results,about the safety switch in the S4 MAF heres what i did,back in the late 90s GM cars came with a oil pressure actived fuel pump(something like that) The fuel pump only runs when a sensor located at the block or sending unit sees oil pressure then a relay will activated the fuel pump so my brother installed a similar system on my car