Why is that you ask? because even I was totally taken by surprise at how well it worked and I wanted to be certain before I posted up my results.
I also needed to be sure that it worked as I know that I'll be facing a substantial amount of backlash from the lemmings who insist that you can't improve on the stock intake. Fact is, you can, end of story...
When an OEM manufacturer designs an intake, performance likely isn't even at the top of the list. Noise concerns, cost concerns, fitment, etc.... are all factors that OEM manufacturers take into account when designing an intake system.
So with no further adieu, here is is...
I based it on the BMC CDA. However, in my case, I ended up buying a Chinese Knockoff from blinglights https://www.amazon.ca/318i-Intake-Mo.../dp/B01LRELJ48
Here's a rough idea of what the inside of my intake looks like (it's not exactly the same as the BMC design, but it's quite similar)
However, when I got it, I found out that it was 2.5 in OD, not 2.5 in ID. so I took some 3 in PVC piping and the bellmouth from an extra S4 airbox I had lying around and opened the intake up to 3 inches so it was perfectly even with the rest of the intake tract.
From there, I ran the hose that came with the kit into the fender well
While it felt pretty good that way, I was hoping for a little more. That's when I got the idea to cut down the hose portion that ran above the auxiliary cooler and splice it back into the intake. Now, while this hose may not look like much, it's about 5cm in diameter, which isn't chump change when you consider that the airflow into the intake is pretty much a function of the combined area of all the inlets.
(sorry, but I didn't get a pic of what it looked like when I was done, I was in a hurry to get it done
In any event, the addition of that last bit seemed to be just what it needed!!! As soon as I took it out for the first test run I could feel a noticeable difference all through the rev range.
Now, of course the inevitable response to this is that it's all in my imagination, there's no way that I could have improved on the magic Audi airbox, not without some sort of dark sorcery
.Well, I contained my enthusiasm and logged the car over the course of the next few weeks and here are the results:
I'll begin by saying that the gains have been consistent over the last 8 weeks. To demonstrate the end result, I picked three days at random from my logs, plugged them into EFI Analytics 'Megalogviewer HD' and overlaid the pre and post intake MAF readings (close relationship to HP) as well as the ECU measured load (very close relationship to torque).
As you can see, the intake system MAF readings were consistently 20-25 g/sec above the stock intake (divide by 0.8 for HP) and the ECU measured load was consistently about 10% higher. So, if you were to take the average of the maf delta at 20 g/sec, divide by 0.8 that would equate to an average of 25 CHP. Same with the torque figures, 10% of 300 ft/lb would be an average of a 30 ft/lb increase.
However, as the title says, I'm gonna go conservative and figure that the intake is worth 15-20 CHP and same for ft/lb.
Blue line is post intake, Orange line is pre intake.
So how is it that this intake can make this much of a difference? I suspect that it has to do mainly with fact that unlike the stock airbox, which has the air pulses exiting into a sealed box and only about 18 inches of intake tract, the design that I came up with has the pulses moving along a 3-4 foot intake tract which ends with a straight shot to the low pressure zone at the end of the tube.
Couple things to note for those familiar with resonance pulse theory.
1) The air in the intake system is not a constant flow, rather, it is a collection of pulses which are generated when the intake air column hits the closed intake valve, from there, the column of high pressure air reflects back until it encounters a low pressure zone, at which point it reflects back towards the engine. This can occur several times before the air is finally drawn into the combustion chamber ( in fact, most pulse tuning uses the 3rd or 4th harmonic).
2) the longer the tube, the lower the portion of the RPM band the resonance tuning occurs within. I suspect that the stock airbox intake tube is too short to provide any resonance tuning effect at any speed that the S4 engine operates in. However, by extending the intake tract to 3-4 feet, a resonance effect can occur within the engine's RPM band of 640-6800. Look up some of the Nissan Infiniti long tube ram intakes and you'll see the same effect.
3) there's some evidence that the BMC design, with it's internal design flows more air than a regular panel filter. Add to that the bellmouth that I used, and I think that the air filter I made flows air quite efficiently.
4)Finally, although it has nothing to do with resonance theory, I've found that even in the hottest summer months that the IAT's weren't too bad. They would rise if the vehicle was stopped (say at a light), but they dropped off just as fast once I got moving. Further, I think that I'll probably make a partition out of some sheet metal and DEI hear wrap and attach it the frame rail. That ought to insulate things quite nicely.
In any event, make what you will of my results. I'm sure that there will be some for whom there is no convincing. That said, I couldn't care less about that crowd. The ones who matter are the ones who are interested in making one of these themselves. If you do, let me know how it turns out and as always, if there are any questions I can answer, please go ahead and ask.
Cheers
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Originally Posted by p3u
) ECU calibrations doesn't equate to a performance increase. 
<--- just imagine thats a middle finger lol
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