Why Ram air does not work.....

[Hypsi87]

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

[CamaroSSBoy346]

You thought of this while sitting in your lecture? Damn. MASSIVE bordom. lol

[oldsaltdoggie]

Now i'm no math teacher but this just dosn't sound right to me 800 cfm Does mean 800 Cubic Feet per Minute ! And we are talking about air being suck in to a motor! I found this on Edelbrock.com

Formula for CFM
CFM = CUBIC FEET PER MINUTE


A measure of air flow into and out of an engine (CFM = CID x RPM x VE ÷ 3456). Example: What CFM is consumed by a 355 CID engine at 4500 RPM if VE = 105% (1.05)?

CFM = 355 x 4500 x 1.05 ÷ 3456 = 485 CFM

Example: What CFM by the same engine at 6400 RPM if VE has fallen to 95% (0.9)?

CFM = 355 x 6400 x 0.95 ÷ 3456 = 625 CFM

CFM Rules...
CFM and Carburetors: Carburetors are rated by CFM (cubic feet per minute) capacity. 4V carburetors are rated at 1.5 inches (Hg) of pressure drop (manifold vacuum) and 2V carburetors at 3 inches (Hg). Rule: For maximum performance, select a carburetor that is rated higher than the engine CFM requirement. Use 110% to 130% higher on single-plane manifolds . Example: If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. A 750 would be right. An 850 probably would cause driveability problems at lower RPM. A 1050 probably would cause actual loss of HP below 4500 RPM. For dual-plane manifolds use 120% to 150 % higher.
CFM and Manifolds: Manifolds must be sized to match the application. Because manifolds are made for specific engines, select manifolds based on the RPM range.

CFM and Camshafts: With the proper carburetor and manifold it is possible to select a cam that loses 5% to15% of the potential HP. These losses come from the wrong lift and duration which try to create air flow that does not match the air flow characteristics of the carburetor, manifold, head and exhaust so volumetric efficiency is reduced. An increase in camshaft lobe duration of 10 degrees will move the HP peak up 500 RPM but watch out, it may lose too much HP at lower RPM.

CFM and Cylinder Heads: Usually, cylinder heads are the limiting component in the whole air flow chain. That is why installing only a large carburetor or a long cam in a stock engine does not work. When it is not possible to replace the cylinder heads because of cost, a better matching carburetor, manifold, cam and exhaust can increase HP of most stock engines by 10 to 15 points. To break 100% Volumetric Efficiency, however, better cylinder heads or OEM “HO” level engines are usually needed.

CFM and Exhaust: An engine must exhaust burned gases before it can intake the next fresh charge. Cast iron, log style manifolds hamper the exhaust process. Tube style exhaust systems are preferred. But headers are often too big; especially for Performer and Performer RPM levels. Improving an engine’s Volumetric Efficiency depends on high exhaust gas velocity to scavenge the cylinder but this will not happen if the exhaust valve dumps into a big header pipe. On the newer computer controlled vehicles it is also important to ensure that all emissions control devices, and especially the O2 sensor, still work as intended.

CFM and Engine Control: Spark timing must be matched to Volumetric Efficiency because VE indicates the quantity of charge in each cylinder on each stroke of the engine. Different engine families require distinctly different spark advance profiles. And even engines of equal CID but different CR require their own unique spark advance profiles. Rule: Expect 0.1% to 0.5% loss in Torque for each 1 degree error in spark timing advanced or retarded from best timing. Also, detonation will occur with spark advanced only 3 degrees to 5 degrees over best timing and detonation will cause 1% to 10% torque loss, immediately, and engine damage if allowed to persist.



P.S What was the four hour training lecture about? LOL

[BigDanTheMan]

i am very impressed with you finally finding a use for all that algebra that was taught to me in highschool. but i thought ram air was designed to reach colder; more dence air.

[Hypsi87]

Originally Posted by oldsaltdoggie

Now i'm no math teacher but this just dosn't sound right to me 800 cfm Does mean 800 Cubic Feet per Minute ! And we are talking about air being suck in to a motor! I found this on Edelbrock.com

Formula for CFM
CFM = CUBIC FEET PER MINUTE


A measure of air flow into and out of an engine (CFM = CID x RPM x VE ÷ 3456). Example: What CFM is consumed by a 355 CID engine at 4500 RPM if VE = 105% (1.05)?

CFM = 355 x 4500 x 1.05 ÷ 3456 = 485 CFM

Example: What CFM by the same engine at 6400 RPM if VE has fallen to 95% (0.9)?

CFM = 355 x 6400 x 0.95 ÷ 3456 = 625 CFM

FM Rules...
CFM and Carburetors: Carburetors are rated by CFM (cubic feet per minute) capacity. 4V carburetors are rated at 1.5 inches (Hg) of pressure drop (manifold vacuum) and 2V carburetors at 3 inches (Hg). Rule: For maximum performance, select a carburetor that is rated higher than the engine CFM requirement. Use 110% to 130% higher on single-plane manifolds . Example: If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. A 750 would be right. An 850 probably would cause driveability problems at lower RPM. A 1050 probably would cause actual loss of HP below 4500 RPM. For dual-plane manifolds use 120% to 150 % higher.
CFM and Manifolds: Manifolds must be sized to match the application. Because manifolds are made for specific engines, select manifolds based on the RPM range.

CFM and Camshafts: With the proper carburetor and manifold it is possible to select a cam that loses 5% to15% of the potential HP. These losses come from the wrong lift and duration which try to create air flow that does not match the air flow characteristics of the carburetor, manifold, head and exhaust so volumetric efficiency is reduced. An increase in camshaft lobe duration of 10 degrees will move the HP peak up 500 RPM but watch out, it may lose too much HP at lower RPM.

CFM and Cylinder Heads: Usually, cylinder heads are the limiting component in the whole air flow chain. That is why installing only a large carburetor or a long cam in a stock engine does not work. When it is not possible to replace the cylinder heads because of cost, a better matching carburetor, manifold, cam and exhaust can increase HP of most stock engines by 10 to 15 points. To break 100% Volumetric Efficiency, however, better cylinder heads or OEM ?HO? level engines are usually needed.
CFM and Exhaust: An engine must exhaust burned gases before it can intake the next fresh charge. Cast iron, log style manifolds hamper the exhaust process. Tube style exhaust systems are preferred. But headers are often too big; especially for Performer and Performer RPM levels. Improving an engine?s Volumetric Efficiency depends on high exhaust gas velocity to scavenge the cylinder but this will not happen if the exhaust valve dumps into a big header pipe. On the newer computer controlled vehicles it is also important to ensure that all emissions control devices, and especially the O2 sensor, still work as intended.

CFM and Engine Control: Spark timing must be matched to Volumetric Efficiency because VE indicates the quantity of charge in each cylinder on each stroke of the engine. Different engine families require distinctly different spark advance profiles. And even engines of equal CID but different CR require their own unique spark advance profiles. Rule: Expect 0.1% to 0.5% loss in Torque for each 1 degree error in spark timing advanced or retarded from best timing. Also, detonation will occur with spark advanced only 3 degrees to 5 degrees over best timing and detonation will cause 1% to 10% torque loss, immediately, and engine damage if allowed to persist.



P.S What was the four hour training lecture about? LOL

It was just a formula to detrmine the speed of 800CFM of air in a 3'" in a 4" pipe. nothing about engine effficency and what not. I don't know to me they need to rename ram air. Too many people think that ram air accually Pushes air in their engine. The training lecture was about Safety and general job proceedjures. (Can't spell) Boring as heck. Even if your engine only flows 400 CFM the intake pipes on a stock car are not even close to 3" so even if the the CFM is lower the pipe restriction is greater. Bernulies pricipal. The air will have to go faster through a small tube

[SkylineUSA]

So, if air is coming into the engine that fast, why does it not come out that fast

I work with weather systems as well as Radar, Radio, Satellites, and Navigation. We have a wind speed meters that work with small ceramic heating elements, these elements are heated 100* above ambient temp. The amount of current it takes to heat the element back to 100*, it can tell how fast the wind or air current is.

When we de-mil these wind sensors, i hope to get one. I will hook one up inside of an intake and see if your formula is correct.

When I was going over your formula, it makes perfect sense, but I also like hands on type testing to back up the science or math in this case

[Hypsi87]

Originally Posted by SkylineUSA

So, if air is coming into the engine that fast, why does it not come out that fast

I work with weather systems as well as Radar, Radio, Satellites, and Navigation. We have a wind speed meters that work with small ceramic heating elements, these elements are heated 100* above ambient temp. The amount of current it takes to heat the element back to 100*, it can tell how fast the wind or air current is.

When we de-mil these wind sensors, i hope to get one. I will hook one up inside of an intake and see if your formula is correct.

When I was going over your formula, it makes perfect sense, but I also like hands on type testing to back up the science or math in this case

Yea so do I, keep us posted on weather or not you get one of thoes sensors. It was just something to do.

[DrJay]

Originally Posted by SkylineUSA

We have a wind speed meters that work with small ceramic heating elements, these elements are heated 100* above ambient temp. The amount of current it takes to heat the element back to 100*, it can tell how fast the wind or air current is.

When we de-mil these wind sensors, i hope to get one. I will hook one up inside of an intake and see if your formula is correct.

I'm not sure how old this thread is but it caught my attention. Anyway, thats actually how the MAF sensor works...just thought I'd throw that in.

[kulak]

Ram Air is nothing more than a fancy Cold Air Intake. Ram Air setups cannot pressurize air in their current form.

I don't have a link to the math, there is a page out there somewhere that explains the math used to explain the reason.


You would have to radically redesign Ram Air for it to work, not to mention, given the best possible intake configuration you would need to be traveling at supersonic speeds to see any measureable increase in air pressure.


Ram Air does get you cooler, more dense air, wich is always good, but it is not any better than a good CAI will get you. Plus you introduce increased drag, without a justified performance gain to account for the increased drag.


Ram Air is not bad, and if you have one there is no reason to run out and switch to something else, but there is not special "Ram Air" effect that gives you some magical performance jump that you cant get out of a quality CAI setup.

[zx2srdotnet]

thats why a lot of "ram air intakes" fro I4's put a tub that not only does into teh fender but it comes out at teh bottom of the front bumber so that it gets colder air and that it doesnt mess with the flow lines of the car. it is basicly a more efficient CAI but not a HUGE improvement

[kulak]

very true, your basically splitting hairs at that point anyhow.


and where do you draw the line what you call RAM AIR or CAI.


IMO they are all just CAI's and should be treated as such, and their performance based on the quality of design and get rid of the entire myth of a "RAM AIR effect" because it is just bogus.

[BigDanTheMan]

whoa, i remember this post! it's like ten months old!

[Hypsi87]

mee tooo lol, you know on every forum there is a rule about diggin up old posts but people always do it. If this thread caught your attention, then start a new post and post up a link to this thread. Or something like that. Thread closed

[GTStang]

This is a very old thread and like Hypsi said if your really ant to talka bout this start a new thread about it. Closed cause he forgot to LoL