ram air intakes? - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-31-2005, 05:27 PM   #11
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Quote:
Originally Posted by dblack1
ok in nascar they have the intake between the hood and the winshield where the high pressure is at, and in nascar applications they can get positive boost
They also have specialized/custom built engines....
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Old 01-31-2005, 06:26 PM   #12
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they do get positive boost, and i was mearly saying that it was a high pressure area.
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Old 01-31-2005, 06:27 PM   #13
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Keep in mind that Ram Air is a term coined in the days of Carburetors and good size hood scoops. Even then though, I don't think it was for induction force as much as breathing cool air.
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Old 01-31-2005, 07:01 PM   #14
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Quote:
Originally Posted by swartlkk
Quote:
Originally Posted by dblack1
ok in nascar they have the intake between the hood and the winshield where the high pressure is at, and in nascar applications they can get positive boost
I still highly doubt that the air in the intake is pressurized even at 200+mph. We're talking about an engine that is turning at 9,000rpm here. At 9,000rpm a 350 cubic inch motor pulls in 3.15 million cubic feet of air per minute. That'* a LOT of air. Even at 200+mph you aren't going to get positive pressure anywhere close to the carb. In comparison, that motorcycle (for conversations sake lets say it'* 1 L or ~60 cid and turns 10,000rpm) would require 600,000 cfm of air and (as stated earlier) it only benefitted at air speeds inexcess of 130mph with a scoop facing into the wind.

Now all that technical stuff asside. I assume that given a large enough scoop and the fact that your car could overcome the wind resistance generated, that you could make more power with 'ram air'. But that just isn't practical by any stretch of the imagination.
Wow, when did Demon come out with their 3.15million CFM carbs? One of us is doing our math wrong cause I'm getting about 911cfm with 100% VE.

That aside, I found the math I was talking about earlier:

"Hmmm I was in a coma like state earlier today ( sitting through a four hour training lecture at work). Anyway I was wondering how fast the air in a 3" inlet pipe to the turbo would be traveling if 800 cfm of air was going into the turbo. So when I came up with my anwser it woke me up enough to ask my buddies at work to calculate it for them selves and see what they came up with. I didnt tell them how I went about calculating it to avoid getting them started on the wrong foot incase I was wrong. They came up with the same results as I did. When I asked them how they went about calculating it they had approached it the same way I did.
here is how I did it:

1) I'am going to use standard temp and press for the air

2) area of 3" pipe = pi * radius squared
3.14 * 1.5in * 1.5in = 7.07 in2

3) Inside volume of pipe = area * length
I wanted to know how long a piece of 3" pipe had to be to half an internal volume of 1 cubic foot. I rearanged the equation:
length = volume / area
length = 1 ft3/ 7.07 in2 = 1 ft3 * 144in2 / 7.07in2 = 20.4 ft

4) OK now I know that 1 ft3 is the volume of a 20.4 ft long piece of 3" pipe. I also know that Iam looking for 800 ft3/min. so this is next:
Speed of the air in the pipe (mph) = (800 * 20.4 * 60) / 5280
800 is cfm (ft3/min)
20.4 (ft of pipe for one cfm)
60 (convert from minutes to hours)
5280 (convert from feet to miles)

ANWSER: 185.45 mph!!! Air speed in a 3" pipe with 800 cfm of air moving through it. Makes me shake my head but it appears to be right. I also calculated for a 4" pipe and the speed dropped to 104 mph.

There is no intended point of this. I was just kind of suprized by my answere and thought I would pass it along. BUT....it does make me wonder how much ram effect some of these late model cars get at 60 mph or even 80 mph with the little factory snorkels. Maybe they're just fancy looking cold air induction set ups? it does not ram air.

This is why I don't think ram air works. it might be a cold air intake but it is not ramming the air in the engine"
Courtesy of Hypsi87 on Automotiveforums.com

Ok so you can see how it was done. What he'* saying is that for 800cfm to go through a 3" pipe it would need to be traveling 185mph. This does NOT take into account bends in the pipe which would slow the air down. So you would actually have to be going faster in order to shove 800cfm through the average 'ram air' intake.
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Old 01-31-2005, 07:49 PM   #15
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sorry. Yeah I miss spoke. Forgot the conversion factor... 3.15 million Cubic Inch per minute = ~1800 CFM.

**EDIT** For a 4 stroke engine that will be ~900CFM not 1800CFM
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Old 01-31-2005, 08:12 PM   #16
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Quote:
Originally Posted by swartlkk
sorry. Yeah I miss spoke. Forgot the conversion factor... 3.15 million Cubic Inch per minute = ~1800 CFM
I'm still not getting how you come at that.
CFM = CI x RPM x VE / 3456
So 350cid x 9000rpm x 1.0 / 3456 = 911.45cfm at 100% VE
Even with 150% VE its only 1367cfm.

Am I doing this wrong?
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Old 01-31-2005, 10:19 PM   #17
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I don't know... I just took the CID * RPM * Conversion factor. I really don't know much about what you're getting at, but I was just saying that I doubt very much that there is any positive pressure.

I get it now. I wasn't dividing by the extra 2 for a 4-stroke. Sorry.
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Old 01-31-2005, 10:57 PM   #18
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But now that you remind me of the whole volumetric efficiency standpoint, your numbers of 184mph for 3"diameter and 104mph for 4" diameter are all for perfect VE. So in the real world, those speed would have to be even faster, correct?
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Old 01-31-2005, 10:58 PM   #19
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I think some very valid points have been made here with regards to the fact that ram-air doesn't really do much to increase intake velocity or volume, but it STILL is of GREAT benefit for providing cold intake air, as proven on my own car. Even with my non-sealing heat shield for the intake, I achieve within 5 of ambient air at under 30mph. And my supercharger stays ALOT cooler with it'* external cooling.

I couldn't have a better qualification of these numbers than this:

Quote:
Originally Posted by DrJay
heh yeah, but naturally aspirated too. For cooling, you're dang right its good at its job, I've seen your low A$$ IAT readings ..but it doesn't actually 'ram air' if that makes sense.
He'* one of the few (aside from the WCBF attendees) that have seen my setup.

The work and small amount of money involved in the project were WELL worth it.
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Old 01-31-2005, 10:58 PM   #20
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Quote:
1) I'am going to use standard temp and press for the air

2) area of 3" pipe = pi * radius squared
3.14 * 1.5in * 1.5in = 7.07 in2

3) Inside volume of pipe = area * length
I wanted to know how long a piece of 3" pipe had to be to half an internal volume of 1 cubic foot. I rearanged the equation:
length = volume / area
length = 1 ft3/ 7.07 in2 = 1 ft3 * 144in2 / 7.07in2 = 20.4 ft

4) OK now I know that 1 ft3 is the volume of a 20.4 ft long piece of 3" pipe. I also know that Iam looking for 800 ft3/min. so this is next:
Speed of the air in the pipe (mph) = (800 * 20.4 * 60) / 5280
800 is cfm (ft3/min)
20.4 (ft of pipe for one cfm)
60 (convert from minutes to hours)
5280 (convert from feet to miles)

ANWSER: 185.45 mph!!! Air speed in a 3" pipe with 800 cfm of air moving through it. Makes me shake my head but it appears to be right. I also calculated for a 4" pipe and the speed dropped to 104 mph.
I use twin 9" x 4" scoops that Ram into twin 4" hose for my Firebird.
So that equates to 72 square inches of ramming area.
That must equate to a speed of far less than 100 mph because I know it made a difference for me over simply just the cold air effect.....I experimented before and after, cool air vs. ram air. Not much difference but measureable in the 1/4 mi times (.1 sec)
Calculate all you want but it works for me.

Now I know the 4" hose on my Bonne does not have any pressurizing effect. It is simply ramming cool air into the intake chamber. It works very well because I measure the same temp inside the box as outside ambient temp. When I lost the elbow a few times (blew off at over 100 mph) the temp inside the chamber rose to 10-15 F above ambient...even with the hose drawing air from the frontal area but with no ram effect.
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