Ram Air Intake; Scale MAF?
 

I'm going to be making a custom ram air intake using the stock air intake. I already have a drop in filter and I've heard that this alone can make the engine run rich. Do I need to make adjustments to MAF scaling being that the faster I drive the more air & thus oxygen will be shoved into the intake? I'm on the OFT stage 2 tune, so I'll be data logging both before and after installation.

Thanks,
-Adam

I'm not sure a ram air intake will really be of benefit. The stock box is designed to pull from a region of lower pressure. Opening up the bumper or similar just adds unnecessary turbulence that can be counterproductive. Due to this the MAF sensor readings may change so you may need to change the MAF scale or similar.

Do the custom intake then run with it for a while, you can't hurt anything. Use Torque Pro to watch your LTFT and AFR and see how it looks. If it's way off, rescale the MAF.

Theoretically I would say no, as you aren't changing the shape of the box itself and the filter should slow air down quite a bit and damp out some of the turbulent effects. But I think I remember reading that even removing the front air dam under the factory snorkel messes with stuff at high speed so maybe the filter does less than I thought.

Problem is if you do need to rescale due to ram air effects, your scale will need to be speed dependant. I don't think the factory ecu supports that.

One thing you could try is to put some baffling inside the intake to transfer dynamic pressure to static pressure before the filter, as that's what you are really after if you still have a filter at all. Just keep in mind that the front of the car does the same thing in stock form.

Fixed it for you... :cheers:

If nothing else this will get you a cooler intake charge. IAT = Ambient. Even with a big snorkel there is some increase in IAT with the stock air box. And if you run an oil cooler, ive seen, the IAT quite a bit higher than ambient using the stock airbox. I'm curious to see results and data logs with a ram air.

The thing is that you need to be going at much higher than legal speeds to make the ram air effect worthwhile. The OEM system is designed to reduce turbulence as it improves airflow. It's possible that a ram air system may reduce flow until pressure is significant enough to overcome this, but your talking 80-100mph+

I'm not sure a degree or 2 of improvement of IAT is worthwhile the trade off for worse flow. For FI I can see the possible benefits of this type of system, but it's less of a ram air intake in that regard anyway.

The only reason the MAF voltage output would change based on speed and RPM rather than just RPM alone is turbulence. If you had smooth airflow you would just get higher voltage outputs if you flowed more air. That doesn't require any extra work.

If you assume airspeed through the filter is negligible, then you are correct. In this instance turbulence would not matter either. However, if airspeed through the filter is significant, then the air coming out of the air box would have momentum that varies by speed in a ram air setup. In a straight tube, this would not matter, but the collection point looks like it is immediately after a bend in the stock air box. Because of this bend, varying momentum will vary the amount of air actually crossing the hot wire.

dang, you guys all bring up some really good points... Ignoring the possibility of rescaling the MAF, I think I'll route the ram air tube to end a couple inches away from the stock snorkel so it can breathe normal under low speed conditions. I will shove a bunch of shortened straws in the end of the ram air tube to promote laminar flow like we did back in fluids class haha. It would make sense that turbulent flow would cause the most issues. I wanted to widen the inner diameter of the snorkel to 3" to match that of the ram air tube though...I might just increase the flare on the end of the stock snorkel so that it can capture the rammed laminar flow. Either option will decrease the snorkel's "velocity stack" aspects but would allow larger volumetric flow. This is all before the filter so it shouldn't cause any serious issues?

I like the discussion going on here, and I have a couple weeks before the flexible ram air intake hose ships in from China haha. I think the biggest issue is turbulent air flow...but if I can overcome that then we might end up with a more efficient system.

If the ram air opening does not go straight into the airbox then it's not really ram air and it's rather pointless. I assume there's going to be a velocity stack at the opening to the ram system, it might at least help reduce some turbulence. An air straighter will help, just one like the OEM would be beneficial seeing as there is one by the MAF sensor.

Have you thought about placement of the opening? I'm not up on these thing but it would make sense you would need it in a high pressure area and not a low pressure area. This would then help with calculations on what speed you actually expect to see positive pressure.

Yes re-scaling will help a lot actually. After using VGIs tool my car runs much smoother and trims are all consistent. Trims were about 15% out of wack and AFRs weren't consistent before the rescale.
I also have all of the wind tunnel data you will ever need for the placement you are looking for.

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