Thanks to everyone who answered my question about induction. Also thanks for bringing this "Ram Air" myth to our attention!

This forum rocks.

--Will

If Ram air were useless how come some of the most experienced drag racers use it? I believe that it is beneficial to power by allowing denser colder air into the engine. What makes more power, heated air from the engine compartment or cold outside air?

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87GT 3.4 Turbo Best 0-60 5.2 seconds
http://turbofiero.fierojoe.com/turbo.htm

Here is something I am curious about.

Marvin McInnis posted the gain in pressure at 70 MPH. Any thoughts on the correlation of the pressure gain being negated by the higher demands of the engine for air at higher RPMS? (since a 2.8L engine ex: at 1000 rpm, is flowing twice as much air at 2000 rpm, etc.) Trying to wrap my head around this, would the potential pressure be negated by the fact that the engine is sucking in more air? Anybody calculated the air velocity say at the engines torque peak or power peak where it is performing at max efficency?

And if the engine cycles through RPM ranges (gears) unlike an airplane engine, wouldn't that cause there to be only short periods of time where a potential boost could help? Dependent on speed versus engine RPM?

[This message has been edited by godalex (edited 10-09-2002).]

Some of you are confusing the Ram Effect as read by someone on the previous page with the operating principle of Ramjets.

Ramjets work at supersonic speeds at which airflow becomes highly compressible. Cars don't go this fast, so they don't have compressible flow.

Here's how ram effect works in cars: Pressure is exerted on a surface by molecules bouncing off that surface. The speed of the molecules (temperature) and the number of molecules (density) determines the amount of pressure. For an object moving at speed, the effective speed of the air molecules is increased, thus pressure increases. The effect is small at car speeds because the speed of the molecules in the gas is much higher than highway speeds.

I don't see where your difficulty is in this.

If you consider the atmosphere to be one big box and, at sea level, having a pressure in that box of 29.92", that is the "force" exerted on whatever needs air. Your throttle body, your lungs, whatever.

Now if we increase that force through the use of turbos, superchargers, or even ram air, even if it's just a tiny amount, the force is still increased over what it would be without any action being taken.

IOW, the pressure is still there. If, for instance, your engine is running and showing a MAP of 20.00", and you figure out a system that will cause a 1" increase in MAP, then it's 21" (at the same throttle setting and rpm). Because you open and close the throttle, your MAP in the plenum will change, but it will be approximately that same 1" higher than it would be without the ram air effect.

NOTE: I AM NOT SAYING THAT RAM AIR WILL GIVE YOU 1" OF INCRESED MAP!!! That is simply a number pulled out of the air to use as an example.

John Stricker

quote Originally posted by godalex: Here is something I am curious about. Marvin McInnis posted the gain in pressure at 70 MPH. Any thoughts on the correlation of the pressure gain being negated by the higher demands of the engine for air at higher RPMS? (since a 2.8L engine ex: at 1000 rpm, is flowing twice as much air at 2000 rpm, etc.) Trying to wrap my head around this, would the potential pressure be negated by the fact that the engine is sucking in more air? Anybody calculated the air velocity say at the engines torque peak or power peak where it is performing at max efficency? And if the engine cycles through RPM ranges (gears) unlike an airplane engine, wouldn't that cause there to be only short periods of time where a potential boost could help? Dependent on speed versus engine RPM? [This message has been edited by godalex (edited 10-09-2002).]

Thanks, John.

I was thinking in terms of what happens with turbo's as an example. One can have a 12lb boost setting at the turbo and have a drop in the manifold due to restrictions, pipes, intercooler, what have you. I wasn't sure that by the time the air found it's way through the throttle body that the potential increase how ever slight might not find itself negated dut to other factors.

Similar to the problems in electron flow, where voltage = pressure or potential push, and current = flow. Larger wires are often necessary to lower the resistance to counter the voltage drop of a long run. Battery voltage is the same measured at the battery, but not when measured further down the line. So my particular "headhasle" was that by the time air went through the duct and throttle body, potential gain would be lost. Now I see that since those losses are there in fact anyway at lower pressure, that greater push (more pressure) would still effectively translate.

Ahhh, now I'm on the same page you are.

Think of the ambient air pressure as the initial push. It's there. If everything downstream is PERFECT (which it never will be), then it will be the same at the other end.

Now if you can give it a little bigger push, that can help overcome some of the restictions and other problems downstream. Not all of them, but maybe moderate them some. That's why the intake side of a forced induction engine is less critical.

Putting forced induction aside, even a moderate to light ram air will help out but at normal speeds only very slightly.

I look at street "ram air" systems like this. It's a way to send colder air to the engine and if we can add just a tiny bit of push, more's the better. I realize there's not much there, but I'll take what's out there, especially if it comes by way of something I'm already doing.

John Stricker

quote Originally posted by godalex: Thanks, John. I was thinking in terms of what happens with turbo's as an example. One can have a 12lb boost setting at the turbo and have a drop in the manifold due to restrictions, pipes, intercooler, what have you. I wasn't sure that by the time the air found it's way through the throttle body that the potential increase how ever slight might not find itself negated dut to other factors. Similar to the problems in electron flow, where voltage = pressure or potential push, and current = flow. Larger wires are often necessary to lower the resistance to counter the voltage drop of a long run. Battery voltage is the same measured at the battery, but not when measured further down the line. So my particular "headhasle" was that by the time air went through the duct and throttle body, potential gain would be lost. Now I see that since those losses are there in fact anyway at lower pressure, that greater push (more pressure) would still effectively translate.

Great rationalism! I love it.

But just to make it clear, Ram Air is not a myth. It is just not possible up to about 350 mph at sea level. Otherwise, the Scram Jet designers at Boeing are wasting a lot of time.

This stuff never 'randomly' starts to work once you attain a certin speed kids...

It's a simple logarythmic equation* (If you don't know what that means, pass high school math.)

It's just not so much that you'll notice an 'oh wow' gain, but 1-2% is not out of the question at ~170mph.

Can't find the exact numbers now, can someone look up static pressure gain in aitstream?

*=when subsonic.

Best!
Ben.

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Ben Cannon
88 Formula, T-top, Metalic Red. (2:13.138 at Sears Point) "Every Man Dies, not every man really Lives"
88 Formula, Northstar, Silver, In-Progreess. -Mel Gibson, "Braveheart"

remember this is a {b] car [/b] not an airplane! Pontiac calls it ram air and your calling it air ram used on jets. Its different! Hell, Pontiac probably used this term before anyone else. Are you dening the fact that when driving air goes into the scoop? When your drving at 70mph, isnt air goin 70mph into it? Its raming air into the engine isnt it? enough to make signifigant hp numbers, no but its there. really its hard to prove this. when its on a dyno its notgoing 70mph into the wind so no ram air effect, if you use a G-Tech at that speed you cant match it to the dyno numbers because one of them will be off anyway. Only real way to test it is to put it on a dyno, dyno it and see what power it puts outs, them put like a big fan in front of it and make it blow air out at about 60-70mph then dyno it again.

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--Adam--
1987 Blue GT 5-speed
IM AOL: GTFiero
What oil leak? That puddle under the car is just sweat from all that horsepower.

quote Originally posted by Toddster: Great rationalism! I love it. But just to make it clear, Ram Air is not a myth. It is just not possible up to about 350 mph at sea level. Otherwise, the Scram Jet designers at Boeing are wasting a lot of time.

And here's the bone of contention!

It's not that it's not possible. It doesn't magically become relevant above a certain speed. Speed is a continuum. The only speeds that are favored in fluid dynamics are zero and sonic. Equations don't care about 70 mph or 170 mph or 370 mph. The speed of sound and zero are the only speeds that are special in the equations.

Anyway, we're talking about a 1% of atmosoheric pressure effect at highway speeds, while a ramjet requires several hundred percent of atmospheric pressure to work. The difference in the magnitude of the effect is just the difference of the squares of speed.