Firewall intake???
 

I have been thinking about where to route my intake pipe and i was wondering if the cold air from the firewall is a adequate "cold air intake" spot. I would like to find cold air without having to cut up the fender/wheel well. I have a single side intercooler (both hot and cold side pipes come from the same side) so there are pipes in crossing the front of the engine.

Could i route the intake pipe to grab air just below the radiator fan behind the sway bar? would i have to worry about dust/moisture?

Just trying to find some clean cold air thanks in advance

I dont see this a lot with turbo cars but it could probably be done.
http://96k.com/miata_stuff/aircraft_intake7.jpg
http://96k.com/miata_stuff/aircraft_intake8.jpg
http://96k.com/miata_stuff/aircraft_intake5.jpg

ganked from this thread
MX-5 Miata Forum - My home-made cowl / cold air intake - Aircraft Spruce ducting

does that have any risks such as sucking in water? that would be my main concern

I dont see anything stopping it from "sucking" in water? :hustler:

When it rains that spot drains alot of water.

Do a fenderwell intake or headlight lid setup :hustler:

I had a home made intake for about 3 months on my car like that when it was N/A.

Rain is no problem, unless your drian there is clogged and it like fills with water lol.

Did it make an effect? Well, it sounded cool...

Cowl induction is a proven successful mod on thousands of performance cars over the last forty years. It has been a factory performance feature on many cars over the years as well.

The area at the base of the windshield is at a slightly higher pressure than the air underhood, so it helps to feed air to your engine just a little bit better. It has been proven in the wind tunnel to be a superior design to most low stock hood scoops (like the ones on my GTO). The scoops don't outperform cowl induction until they get over 2 inches or so above the hood surface. This is due to boundary layer stagnation.

The second benefit is, of course, the air is much cooler than underhood air. That is actually the greatest benefit.

Thirdly, some of the factory and racer cold-air mods were bad about sucking up water and road debris ('66 Olds 442 for instance) from in front of the radiator, below the front bumper, or in the fenderwell. For brake ducting it isn't an issue because water or debris and dirt aren't quite as harmful to the brakes (minus warpage). The cowl area is as high out of the debris as you can go to easily find clean, cool, higher pressure air.

These are some of the same reasons that Trans-Am and NASCAR and many American Le Mons Series race cars take advantage of cowl induction. And that Aircraft Spruce and Specialty kit looks sharp, but I would DIY.

LOL, the guy purchased a flange and a piece of ducting from Aircraft Spruce, then modified and attached them to his car. Sounds pretty DIY to me already.

:fawk:

It sounds DIY until you start checking prices, though. Spruce is very high on everything.

I'm a cheap bastard. I would find/build the flange for a couple of bucks from the U-Pull-It junkyard, used machinery parts from where I work, or Home Depot.

Yeah that is definitely not a cowl intake kit.

Don't buy the tubing from Spruce. Shop around. I just bought 5' of that same Aeroduct tubing, for the same purpose, from another source, for ~$30 with shipping. You only need about 3 feet. I used this stuff because the materials are good and the interior wall is smooth (for reduced pressure drop) compared to that plastic accordion tubing stuff sold at Pep Boys and the like.

This setup works well; this is what I am using. In my case though I am placing an air filter in the cowl area. I an using a 3.5" dia by 6" length cylindrical K&N filter, two of them in series.

The only thing is that this cowl setup is considerably louder than an under the hood intake. I have used both so I know. During cruise it is fine, but at WOT you can definitely hear it. In fact, if you have the vent on 'fresh air' instead of 'recirculate' it is a little louder since the air intake for the vent is in the cowl area. This setup IMO is not unbearably loud, but definitely not stealthy. It sounds like you have a shop vac under your hood. The high pitch compressor whine is somewhat suppressed by the tubing's resonant frequency.

Attachment 208607

https://www.miataturbo.net/forum/t16531/

Used to be routed to the air box when it was n/a - never had a problem with water.
Attachment 208606

https://www.miataturbo.net/forum/att...8-pict0304.jpg

https://www.miataturbo.net/forum/att...5-pict0247.jpg

https://www.miataturbo.net/forum/att...8-pict0320.jpg

I'd take that bag off before you try to drive that car anywhere. ;)

I need to figure out some kind of CAI. I have a charge pipe running right where most put their intakes. This cowl idea might just work, I just have to buy a filter that will fit. Too bad about it being louder though. Mine is already a little louder than I like at WOT.

Yeah it is louder, just wanted to get that in there before someone does this and then bitches about the noise. But it works well, and it sounds sweet IMO. It is good for a few 'WTF is that' head turns too if that is your thing.

SV650 no offense but I am not sure I like that setup as shown with your stock airbox removed. It would rely on the cowl always being at a higher pressure than the hood area, otherwise it will not work properly. I like the sealed approach better for that reason, like the ones in the other pictures above. Are you going to fabricate a box to enclose the filter?

Sorry to revive a long dead thread, but is this still a viable and worthy while option? I'm highly considering doing this to decrease coldside intake temps.

I don't see why not. I'd like to hear how loud it actually is. Anyone have a decent video ?

Found this, but it's on a stock NB. I'm going to say it'd be louder on an F/I setup.

all i heard was sssssssslllllllllllooooo o o o o o OOOOO O O O O O O O O

I want a quiet intake, how do I do that?

~80kpa on the highway up a long gentle slope is fcking annoying. Those carbon inline air boxes, helpful or not? I've seen FM suggest shoving the airbox full of egg foam, but I'm not doing that.

Right now I just 90 off the turbo into a 3" cone filter in front of the headlight. Was considering a inline air filer to try and quiet things down.

The intake on my new 2863 is vastly quieter than the giant sucking sound on my 2560. Pretty much all of the other bits are the same, so the only conclusion I can come up with is that it's the anti-surge compressor housing.

I'm not sure how helpful that is -- it's kind of expensive way to quiet things down. :)

http://www.codrus.com/miata/fm2r/intake20.jpg

--Ian

Haha, and here I was not wanting to spend $40 on the ebay plastic airbox doohicky! Results are results though :party:

My GTX2867R sings like a Peterbilt under a light to medium load because of the ported compressor housing. It hasn't gotten old yet. I like turbo noises.

Do it, it WORKS! I wrapped my air filter with just one layer of 1" foam, used a couple zip ties to keep it on there, sound went down 80%. No measureable/noticeable change in power or spool. Just a lot quieter.

Ah, alright. I'll give it a shot, not like it's hard to remove if I don't like it and I've got some foam from somewhere...

I loved the noise for a while, but driving the miata all the time means I hear them quite a lot :party:

go to a 4" intake tube.

Be sure to use closed cell foam* for maximum silencing.

The foam filters from Sears large shop vacs are a pretty good fit. Sears.com Cheaper in the store, but it might have just been on sale.


*Do not use closed cell foam. Duh.

Firewall intakes are on every 2nd n/a miata here in australia. Ive done them a bunch of times, including to turbo cars (smallest turbo on a miata ever incoming..)


https://fbcdn-sphotos-h-a.akamaihd.n...afd2eb5363c3ef

Its definately a noticeable thing in the cabin, totally bearable and pretty cool if you like turbo noises, but from in the cabin these intakes are about as loud as it gets.

Dann

I wrapped it with some egg crate foam, that is open cell right? It certainly worked, like a whole lot. AFR and O2 range seems the same, but it's rainy today and I can't much tell if it's much weaker.

Wouldn't having to step down to the tiny t3 from 4" cause an increase in airspeed? Isn't that what makes it squeal like a piggy now?

Another of those carbon air filters, thanks for the input Dann. Think I'll have to pass on one of those now, I want to be all stealthy and quiet.

What boost control is that?

AMS500 with custom (my made) actuator.

I'm not really concerned about the sound generated. I'm more concerned about rain getting in and if it actually makes a difference in regards to turbo intake temps

Had no water ingestion issues with my FM Randal carbon piece last fall. I was curious and after a heavy heavy thunderstorm popped the hood and checked the inside of my airbox, it was dry. The actual Randal carbon thinggy looked like it had a fine mist in it, but nothing was soaked.

Dann, Elior or someone please post links to manufacturers of those tube airbox filter things so I can read more stuff about them. I've wanted to do this for quite some time.

I've found ONE from a company in Canada called PRM Racing but they are assholes and won't give me dimensional drawings of anything in their product line. How the hell am I supposed to figure out what to order if I don't know what will fit?

Carbon Air Filter

Also:
https://www.miataturbo.net/build-thr...e3/#post709118

Yep, I have that same K&N cone thingus sitting in my garage from when we discussed this previously. Thanks H :bigtu:

Perfect. I think I'll get this done at the same time as my FMIC piping re-routing. :makeout:

Guys, thousands and thousands on NA and NB miata all over my country have these. Do the math on the whole 'rain' thing there.

I mean I dont see how the rain could get in them down there. Your rain comes out of the ground and lands in the clouds right?

Really, whats the size opening on the in side on those silicone intakes filters.

They have 3 different sizes on the website. The one I linked is 2.5". The filter on the inside is a cone that comes to a blunt nose, like the filter on Ford trucks. They seem decent for constructing a cold air intake. Certainly at least as good as the K&N Apollo that is many times more expensive.

Wait so the size listed is for the cold air hose? Then what size intake tubing does it fit on is the right question.

Honestly leafy, Is this what you think will happen?

https://www.miataturbo.net/attachmen...ine=1426807724

No. Size listed is for the intake tube. The open end is substantially larger. I used to have one of these and could have taken measurements, but sold it a while back.

Leafy was just making a "Down Under" joke. We know that water ingestion isn't a problem for a cowl intake. Heck, some of us even do water injection on purpose.

I'm still waiting to see someone cover the entire cowl in some sort of mesh. then run a straight tube to the cowl area using a velocity stack.

but this would suffice:

https://www.miataturbo.net/attachmen...ine=1426856252

https://www.miataturbo.net/attachmen...ead-cowl-1.jpg

Brain one of those inline filters with a velocity stack in the cowl could work too. If there's a space in the cowl to fit like a 7" diameter hole for the velocity stack.

There won't be any room in my engine bay for a huge canister filter. I'll try to mount something like pictured above, or fab something up close to what hornetball made; which IMO is one of the nicest filter locations/installs I've seen.

Holiday season means that the silly season for a marketing guylike me is in full effect and I spend my time thinking of ways to improve the Miatini. I.e., reading scientific reports and studies on duct design etc.

My cone filter is attached right on the compressor housing inlet (2.5") of my EFR 6758. I have been wanting to install a carbon airbox with a firewall intake as pictured above to stop drawing in hot air coming of the radiator. At the firewall I plan on installing a 2.5" bellmouth, a gentle 2.5 - 3" expanding tube attaching to the carbon airbox (3" in and out), a 3" 90° aluminium elbow with a gentle radius and to a final 90° silicone coupler that reduces the diameter from 3" back to the required 2.5" at the compressor.

Why the expanding tube?
https://cimg4.ibsrv.net/gimg/www.mia...20dac3c327.jpg
I read an article from Willem Toet talking about expanding intake ducts to convert total positive pressure (as found near the firewall) into static pressure, of which I hope to improve intake losses between the firewall and the compressor. Also see "static regain" for that matter.
Dunning Kruger confusion #1: WRC cars all have CAI, but the inlets going to the air filter box (and sometimes incorporating them) are FAR bigger than 2.5". Matter of fact only subaru seems to have employed an expanding duct (probably more due to packaging restraints).

https://cimg1.ibsrv.net/gimg/www.mia...1df0905fb7.jpg
https://cimg2.ibsrv.net/gimg/www.mia...163da2ed4b.jpg
https://cimg3.ibsrv.net/gimg/www.mia...3d82bf4a22.jpg
https://cimg5.ibsrv.net/gimg/www.mia...93b7b810a.jpeg


So, while Mr. Toet went on to explain the importance of expanding ducts, none of the WRC seem to car about it and mostly rely on dynamic ram air pressure. Anybody got a clue why, or has done some testing? Clearly you try to get the least pressure drop and the least IAT increase. Would the increase in static pressure (firewall intake + expanding tube vs. pod filter behind the radiator) overcome the pressure losses caused by the longer intake?
More reading and real world testing:
AutoSpeed - We Have a Record!
AutoSpeed - Into the Intake - Part 1 (issues 177-180)


Possible efficiency losses due to intake elbows
According to Zhao et al. (and many other researchers, intake elbows not only pose restrictions, but also affect the efficiency of the compressor wheel itself due to non-uniformity of airflow entering the compressor, leading to later spool and worse stalling behavior:
https://cimg5.ibsrv.net/gimg/www.mia...73afc80620.jpg
Investigation of Stall Inception Behavior in a Centrifugal Compressor with Bent Pipe/Volute Coupling Effect
Inlet bent torsional pipe effect on the performance and stability of a centrifugal compressor with volute
And probably the best paper on turbo inlet bends: The influence of inlet flow distortion on the performance of a centrifugal compressor and the development of an improved inlet using numerical simulations
https://cimg0.ibsrv.net/gimg/www.mia...3a79d1c58a.pnghttps://cimg1.ibsrv.net/gimg/www.mia...31fbdf63a4.pnghttps://cimg2.ibsrv.net/gimg/www.mia...a40de1eedb.png

Dunning Kruger confusion #2: there might be more to turbo intake design than IAT, intake pressure and pipe length. As a non-native-speaking non-engineer I#ll try to wrap my head around it and send it in the mean time.

See, now thread resurrection with data is something I can get behind.

I didn't see the point in opening a new thread if it fits the old one (unless Scott and Dann can't keep their shit together :-D )

regarding the intake diffuser: maybe I shouldn't worry so much about gaining static pressure at all. The EFR 6758 at full boost swallows some 0.2-0.25 m³ of air (200-250 liters) per second (!) according to the BorgWarner Match Bot (BorgWarner MatchBot). That's a lot of air flowing through a 2.5" inlet diffuser opening. Maybe it's better to look elsewhere and build a 3D printed intake that goes across the radiator into the mouth, but is designed for turbos

Since I'm sick in bed I cannot do any pressure testing myself, so I have to rely on online calculators. Let's calculate the pressure drop of the aforementioned cowl intake with 2 x 90° bends, all 3" tubing up to the air filter box and from there to the cowl. For now let's assume both the pod filter in the carbon air box and the pod filter attached directly to the compressor housing have the same pressure drop, so we can leave those numbers aside.

Using the Pressure Drop Online-Calculator calculator, we use the following inputs: 25°, 1 bar absolute air pressure, 200 liters per second of air flow (air density 1.225 kg/m³), dynamic viscosity of 0.0185 mPa*s. The pipe roughness for rubber (silicone coupler) and aluminium are roughly (pun intended) the same @ 0.0015 mm.

• 90° elbow, 3" (in reality it tapers down to 2.5" to fit the compressor, but nevermind), silicone. Assumption: 150 mm radius --> pressure drop = 2.41 mbar
• 90° elbow, 3", aluminium pipe. 230 mm radius as given by manufacturer --> pressure drop = 2.39 mbar
• 90 cm of aluminium straight pipe, 3" diameter --> pressure drop = 2.33 mbar
• velocity stack style curved bellmouth 3" inlet: 0.63 mbar

so total pressure drop of a 3" firewall intake would amount to 7.76 mbar or 0.78 kpa (=3.13 inches of water in freedom units)

If we replaced the beginning of the 90 cm straight pipe with a diffusing inlet, starting at 2.5" and expanding to 3" at an half-angle of 10° (https://www.powersprint24.de/reduzie...-900308ps.html), we would have 34 mm of expanding tube and 866 mm of straight 3" pipe.

• 86.6 cm of straight pipe: 2.24 mbar
• 3.4 cm of expanding tube: 0.94 mbar
• velocity stack style curved bellmouth 2.5" inlet: 1.26 mbar

So the diffusing inlet actually is detrimental to performance, at least for high-flowing turbo engines or classes without a mandatory inlet restrictor. With a restrictor a diffusing trumpet might partially recover some pressure, which is probably why they are so carefully tuned.

Learning 1: make the intake pipes as large as possible. Pressure drop in a 2" / 2.5" / 3" / 4" straight pipe of 1 Meter is: 18.6 / 6.03 / 2.59 / 0.65 mbar.
Learning 2: a diffusing inlet has a negative impact at least for this application.
If I have fucked up the math or logic behind this, please feel free to correct me.



So far we haven't touched the issue of relative pressure. We all know that the cowl near the windscreen is a high pressure zone (the mouth might be even higher pressure, but that's a different matter). How high the pressure is I can only guess. A few data points:

• Autospeed #1: At 70 kph (2nd gear @ 6,000 RPM) pressure drop before AFM was reduced from 25 cm/10" of water to 9 cm/3.5" when moving from a stock NA's air filter system to a cowl induction with an enclosed pod filter. Since the filter itself didn't pose much of a restriction, most gains were obtained by a) promoting better flow and b) having positive pressure enhancing the entering of air. 16 cm of water gained equals an improvement of approx. 16 kpa. How much of this we can attribute to (b) i do not know
• Autospeed #2 did some pressure testing with a somewhat rounder Lexus RX300, relative to ambient (cabin) pressure at relatively low speeds (60 kph). However, I'd read the results with a grain of salt when it comes to Miata world applicability - the author recorded lower pressure in the wheel well, while Keith detected higher pressure on his miata
  http://us1.webpublications.com.au/st...10360_10mg.jpg

With 2 additional datapoints at 120 (3") and 150 kph (10" of water) one can calculate that the Lexus has approx. 1.6" water (0.4 kpa) of positive pressure at 100 kph, measured at the base of the windshield. So - as far as I understand it - that means the positive pressure cuts the intake losses in half 0.78 --> 0.38 kpa (1.5" of water) of pressure drop. And if the pressure distribution was a bit in our favor (twice the pressure, i.e. 0.2 inches at 60 kph) we might offset any losses.
The lower intake temps and denser air would then be power found.

To put that into context: Autospeed's best performing intake (Prius) had a pressure drop of 4" of water (albeit including pressure drop caused by the filter)

However, with the mouth being even higher pressure we should really get going with a cobra head intake that draws air from in front of the radiator.

I mean, you are asking an awful lot...