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I bet you did.. you smart cookie you!
So that's how fast we need to be going in order for ram air to be efficient? Somewhere around here, people were saying it was useless under 400mph. But that could have been with respect to air density or velocity.. iunno..

vrg3 wrote: At 6000 RPM, this is 7500 liters per minute or about 27500000 cubic inches per hour.

2.5 inch pipe has a cross-sectional area of about 5 square inches.

So air would be going through a 2.5" pipe at about 27500000/5 = 5500000
inches per hour, or about 87 miles per hour.

You are right. I guess I made a mistake somewhere in my calculations... But 2.5^2=6.25, and overall speed is almost exactly 70 mph, if you don't round anything off. Bummer...

Heres my expierement to demonstrate my theory in practical terms.

Get a cup of starbucks on your way to work.
Finish coffee and acheive cruising speed.
Now roll down your window.......
take your empty coffee cup and point the top (thats the OPEN end) in your direction of travel.

Feel that? take note of the resistance. thats air.... that could be your inlet:lol:

That's true, but what is the purpose of having boost if you are not flooring the gas pedal? What I am saying is that at full throttle and high rpm engine will not have any boost on it until you go over 70 mph. All the air which the cup catches will be consumed by the engine before there will be a chance to create extra pressure. Of course anyone can use a 4 inch pipe to catch the air and then downsize it later on. Since 4 inch pipe has over 2.5 more area, than the speed needed to create boost drops below 30 mph.

yeah, I see. u guys sure are smart w/ yer fancy math and all.
I just "barefoot enjuneer" it. lol
So I have some design issues to resolve, frankly it's not that high on my list. I have the problem of the WRX reservoir relocation to deal w/. I'll revisit this l8r but this discussion has been really helpful in refining my concept.

but considering a 4" would lower the threshold to 30mph. I think I'm on to something. Consider that the foglight bezel is...what 6"?

I've been wanting to engineer something similiar to this, as well, but I'm saving it for when I get around to pulling my bumper off, which, won't be for a while.. it's a day's ordeal.
Getting more air to these engines is definitly a good idea. There's more power to be had, and in many cases, better mileage, which.. to me, is the biggest plus.
Good questions, kidwired, I'm glad you're thinking!!

Years ago, before airboxes were designed as resonant systems, it used to be popular to cut additional holes in the air box to allow more air flow for high rpm. This is no longer a good idea. Modern air boxes can flow much more air than the engine will ever use. Modern engines have throttle bodies or carburetors with throats that are typically about 45mm in diameter, about 16 sq.cm in area. The inlet snorkel to a modern air box will be roughly 300 to 800 sq.cm - much larger than the throttle body or carburetor throat. The idea that the snorkel makes for a significant impediment to air flow into the engine is questionable at best. Drilling holes to let in more air is exactly equivalent to drilling holes in your speaker cabinets to let out more sound. Removing the snorkel from your air box is the exact same thing as removing the port in your speakers, the tube that's carefully engineered to have just the right diameter and length to reinforce the bass on your speakers at low frequencies. By altering your air box in any significant fashion, you're most likely going to cost yourself three to five hp in the mid range, and gain nothing measurable at high rpms.

http://motorcycleinfo.calsci.com/Airboxes.html

In regards to that article, I don't think the snorkel has much effect either way, but I don't see any way you'd lose power from it. Removing the snorkel isn't the same as drilling holes in the airbox (in which case I agree with the article), nor in this case is it analogous to modifying a speaker as intake pulse tuning wouldn't be altered in any measurable way since the large opening to the airbox and the filter itself would effectively cancel any significant pulse effects from that point forward. Mainly I see it as a weight reduction measure and to change the tone of the engine a little as desired. I personally noticed pretty much no difference from stock even with the addition of the external NACA duct to bring in cooler outside ground air. Looks cool, though.

Steve

91legacy_sleeper wrote:
Getting more air to these engines is definitly a good idea. There's more power to be had, and in many cases, better mileage, which.. to me, is the biggest plus.
Good questions, kidwired, I'm glad you're thinking!!

Personally, after recentlly inspecting the heads on our cars, I dont feel an intake will do any good.

Seriouslly, the valves are smaller than the ones in my 1.6 diesel rabbit. You could remove the intire intake assembly in our cars, in theory, and get no better flow into the cylinder. The restriction is in the valve itself, and theres no amount of porting or polishing thats gonna help.

If you want more power, Get new heads.

that brings up a good point. The EJ22t heads would probably be a great NA mod for us EJ22 people. How hard would that be to do up?

Today I de-snorked my Legacy. It was really easy to do. Just remove the air box, and take out the front most screw that holds the wheel well covering in. To get the wheel well covering out of the way just pull the tabs out that are slipped into the bottom of the bumper, once those are popped out just flex the front part of the wheel well cover down and out of the way. I removed the entire snorkus assembly. there are only two bolts that hold it in. one in the air box and one up in the wheel well. after the bolts are out just coax the snorkus assembly out and you are pretty much done. I did one additional thing to make sure that the air was being drawn from the inner part of the fender and not through the gap between the air box and the engine compartment wall. I took a yogurt container and cut the bottom out of it and pushed it through the hole in the air box so that it protrudes into the area that the snorkus tube used to be. The only differnce that i noticed upon a quick test drive was that it has a bit more sound now. It is a nice deep boxer style of sound. You only notice it when you get on the gas a little. No HP increase noticed. I kept the entire snorkus assembly intact so that if I decide I want to put it back in, it is no problem to do.

Hi guys,
I'm in Australia and am doing a PhD in engineering. I also post a bit (very little) on the RSlibertyclub.org forum.

Was trolling through your tech section and came across this and started doing the math

vrg3 wrote:Did you double-check your math? Cuz I come up with something closer to 90 mph:

A 2.5 liter four-stroke engine consumes 1.25 liters of air per revolution.

At 6000 RPM, this is 7500 liters per minute or about 27500000 cubic inches per hour.

Your right up to here so far. all is Good.

2.5 inch pipe has a cross-sectional area of about 5 square inches.

Here is where you make your mistake and the other chap is correct.

Area of a Circle = Pi*r*r
Pi = 3.141592654
=> Area(2.5" pipe) = 3.14 * 2.5*2.5 = 3.14 * 6.25 =
19.634 square inches

So air would be going through a 2.5" pipe at about 27500000/5 = 5500000
inches per hour, or about 87 miles per hour.

Did I get that right?

Answer no!
It's actually about 20mph.

Cheers
Darryl

Hi Darryl!

2.5" pipe has a radius of 1.25".

so its actually a slower speed then?

Slower than what?

djb79 wrote: Area of a Circle = Pi*r*r
Pi = 3.141592654
=> Area(2.5" pipe) = 3.14 * 2.5*2.5 = 3.14 * 6.25 =
19.634 square inches

It's actually about 20mph

vrg3 wrote:Hi Darryl!

2.5" pipe has a radius of 1.25".

20mph

1.25" is the number I used in my arithmetic.

vrg3 wrote:1.25" is the number I used in my arithmetic.

yeah, I guess I'm confused or something

He used 2.5^2 x pi = approximately 20mph

I thought you were pointing out that the radius is actually 1.25, and he should be doing 1.25^2 x pi (which would yield a slower mph figure)

Vikash's original analysis is correct and 80mph is the correct speed. Using a larger radius in the calculation of the area results in a larger area and the larger area is what allows a slower speed. But the larger area is incorrect so 80mph is the right number.

Oh I see. So you'd need to get a nice big hood scoop if you wanted effective ram air.

Correct.