zbomb

gtxracer

First draft of the airbox design - this is a very rough first attempt. This was an exploration of space and size of filter I could cram into the volume. After searching through the K&N catalog with my overall generic dimensions, I found a handful that would fit in the space:



After playing with 3 different sizes and designing the filters in CAD, I threw together the quick housing and started laying it out in reference with the scan. I'm not happy with the slope of the airbox where it passes over the throttle body. Not great for consistent airflow, and I'm out of room. I may have to take the compromise and just go with it, but I'd like to research airflow and how a sloped airbox will pull the air. I've seen a few OEM airboxes with sloped bottoms, but I don't recall one with this steep of a slope and this close to the filter. Of course, I could put this design into CFD and run a flow simulation....which I might do....but again.....laziness.

It'll be a tight fit to keep the OEM vented wing cover. I would design a snap-fit interface for the OEM cover but I also want to play with a ram scoop, both a high and low version. Low for street so it blends into the bodylines, and a high scoop for use with a wing for the track. We'll see, I mostly want to lower IATs and mount a puller fan to sweep air into the engine bay.

Anyway, take a look and I'm open to feedback.





View from behind the engine

circuit.heart

Suspect the leftmost ~20% of that air filter won't be super useful with how shallow the box is at the tip.

Space allowing, I would mirror the throttle inlet tube to form a Y and run two smaller airboxes instead. ​​​​​​ Fewer games to play with the depth, and you can get enough airflow with two easier to package smaller filters.

Random thought, the E39 M5 has two small symmetrical airboxes that can feed a 400-450hp V8. I wonder if the filter dimensions could work here, you'd be able to use a proper Mann/Mahle paper filter instead of K&N.

gtxracer

I think you’re right, air isn’t going to flow much at the shallow end of the box. I thought about two filters, and even saw the Hengst E1056L used in another custom airbox, so I’ll play around with those and look into other sizes that would fit.

I referenced my conical air filter and calculated the surface area to be around 110 sq in. I think this is on the lower end of the spectrum for a healthy V8 engine, and the long thin filter above is around 125 sq in depending on actual filter area. I’d like more, and two separate filters might give me that. Hoping for over 150 sq in. I also really like symmetry, especially in an airbox, so I’ll explore the dual filter design and report back. I know the left side of the engine bay has less room due to the valve cover breather and the catch can, but those could be moved I think.

Also, +1 on a paper filter. Unfortunately K&N has the easiest catalog to explore and I cross reference each filter to its application so I might find a paper version. The above filter is for a 928, so a paper filter should be available.

Thanks for your input, circuit.heart. Much appreciated!

theprf

My Cayenne has two separate airboxes on opposite sides of the engine bay with a Y pipe going to the throttle body. It's good enough for 550+ HP....

gtxracer

Unfortunately I don't think there's space for a Y pipe, at least not easily. The LS3 throttle body actuator is huge, and sticks off the to the side and takes a ton of space. See below:

zbomb

The intake situation for LS cars really pretty much blows and that humongous actuator makes an already ****ty situation worse.

I'm glad someone smart like you is endeavoring to make something better than what everyone does which is varying degrees of not so great. Although, my setup is so wonky, not sure anything made for anything but it would work.

Godspeed amigo.

gtxracer

Thanks Jason. Not sure if I can make this one happen, but I'll keep plugging away.

A ram intake would make much more space, which is essentially what we need. On a car like yours, you'd barely see it, but I don't run a wing (yet), so it's a fork in the road for me and I need to make a decision.

edit: like this: https://rennlist.com/forums/996-gt2-...air-scoop.html

gtxracer

Researching the flow rates of modern V8 engines, I see the general rule is intake speeds are 100 m/s or ~224 mph for standard engines and 115 m/s or ~258 mph for race engines. The formula to calculate surface area needed for an air filter is based on air flow rate. I did some maths, then cross checked here and found at 7000 rpm my flow rate should be about 700 CFM.

To calculate the required surface area for an air filter, you will need to know the air flow rate (in cubic feet per minute) and the air velocity (in feet per minute), then use the formula: surface area = air flow rate / (air velocity * 60).
Reference: https://www.physicsforums.com/thread...e-area.987902/

For LS engines, I'm using 224 mph (100 m/s). 700 CFM/ (224 mph * 60 mins/hr) = 0.052083 cubic feet or exactly 90 cubic inches, or in a filter's case, 90 square inches. This is a 9 x 10 inch filter. A conical filter, like the Uni filter on the car now, is 6 inches in length with a ~3 inch radius. Area for the outside of a cylinder = 2*pi*r*h. For my uni filter, this is 113 square inches. I like to run larger filters on my cars, essentially to over-filter and offer more than enough air, but this is a street car, not my Raptor or race Jeep. So I think I could reduce filter size, cross reference other platforms filter sizes, and make this my min filter size needed and design around that.

More to come, someone chime in if I'm off base. Thanks!

gtxracer

Alright, v1.2...this is a 11.5x9.0 filter and fits the bill for at least 90 sq in. and was used in up to 4.0L Dodge Nitro applications. I'd like it to be bigger, but this is the largest I can fit into this space without significant compromises somewhere else. I would say this makes a good street filter for casual driving. I'll want to take a high resolution 3D scan of the engine compartment only and ensure everything fits, and I'll order a filter to scan and finalize the CAD before 3D printing an initial prototype. Of course, I have to add mounting tabs and incorporate the spoiler cover.

Let me know your thoughts!

edit: My next idea is to expand the side of this new design with a slope for a bit more air filter area in the even it's needed and the engine would pull it from available space if there's a reduction in the closer areas.

cdk4219

What do you do if it rains, or you wash the car?

gtxracer

Move to SoCal, don’t wash your car.

Not there yet but I’m planning to not spray water in that area and will come up with a plan for rain. The GT cars with ram intakes don’t have much there for rain mitigation. I don’t drive the car much in the rain but want it to survive a sudden downpour if needed.

Porschetech3

They make "Rain Socks" or Hydro-shields" for open round air filters to keep them dry, but unfortunately they don't work for enclosed flat air filters...

allcool

True, used many on my off road and sand cars...

Outerwears, makes them that fit K&N perfectly and ones that fit the top of airboxes. And they also sell the material to make your own.

If it were me, I'd give Outerwears a call...

Just not sure all of them are 100% to stop a sudden down pour. And all it takes is a small amount to hydrolock...
IIRR they make different type materials, some might stop 100% water intrusion... Can't hurt to ask.

gtxracer

That's a great solution and I appreciate the idea! I'll give them a call. Thanks to both of you.