FACT or FICTION: Would be interested in hearing your guys opinions.

It's not a matter of opinion if it works or not.

It's a matter of fact, it either works or it does not, no opinion involved.

My opinion, done right, there is no downside. Doing it right, is not always easy or obvious.

I also suspect most reports of gains, are more from getting a cooler air inlet source, rather then any 'ram' effect.

Cold air is better than warm air

Fiction.

You can "ram" as much air in there as you like, but it won't make fart in the wind difference: there's a thing called an air filter standing in the way.

So after 100? years of racing,rearward facing "ram" scoops should be rather common if indeed its a myth, even in race cars without filters?

Some of the homebuilt airplane guys that use a special shaped inlet for their engines, even with an air filter say that it will give a extra inch of manifold pressure.

cold(er) air & I think there'd have to be some pressure increase. It'd have to have some bennie, maybe alot. No actual back to back testing done here tho

My 64 ran 145 with a scoop, 147 with the same scoop sealed to the hood.
Doug

Much R&D went into the development of this hood...


It ain't an ornament...

Ram air works great! The problem is figuring out the correct carburetor mixture from idle to the speed where the ram air works the best without being too rich at idle to that point and when too much air will lean it out!

Grab some air

Absolutely works. I've made my own from junk many times... the car always picks up.

Problem with the examples given in this thread is that most, if not all, of the improvements are due to not using warm under hood air and are not due to ram air effect. NASA did some testing and it really isn't until you hit 100 mph that any noticeable effect is seen. Of course design (getting above the boundary layer)is important and I don't see any of the pictured scoops designed to do that. I suspect that the mixture issues mentioned are due more to turbulence of the airflow through the carb than a pressure increase in general, after all that is what makes a carb work.

For a street cars, it's for looks. A race car may see ram air effects at the top end of the run.

Old post for geeks getting into the facts of ram air
=====
Page 415 of the Bosch Automotive Handbook, 5th edition

has the two equations you need
to see how horsepower and torque change
when either temperature or pressure change.

For temperature the offical equation
used by Americans (SAE) Europeans (ISO) and Japanese (JIN)
is:

{ Temperature Before + 460/Temperature After +460} raised to exponent 0.6

you need a scientific calculator to do this
but there is one built into every Windows computer
under Start...Accessories

As an example,
say that your re-locate your air inlet to a spot where the air temperature
drops to 80 degrees
when before the air coming in had been 100 degrees.

{100 +460 divided by 80 + 460} raised to exponent 0.6

={560/540} raised to exponent 0.6

= {1.037} raised to exponent 0.6

= 1.022

You mulitply this number times your horsepower or torque
so if your engine.
If your engine makes 230 hp at peak
1.022 times 230 = 235 horsepower with the 20 degree lower air temperature.

You may have heard the 'Rule of Thumb' that each 10 degree F reduction in air
temperature improves horsepower by 'about' 1% and the equation above is where
that comes from, but is more accurate

For corrections when the pressure changes
the following equation is used:

{absolute pressure after/absolute pressure before} raised to exponent 1.2

As an example
say that the weather is changing where you live
and one day the weatherman says the pressure is
29.5 inches of Mercury as a stormy "Low" passes over
then the next day a clear sky "High Pressure Area" passes over
and the pressure rises to 30 inches of Mercury

{30/29.5} raised to exponent 1.2
{1.0169} raised to exponent 1.2
= 1.0204

It is important to realize
that built right into your engine
are IAT (intake air temperature)
and MAP (manifold air pressure)
sensors.

Your IAT and MAP sensor outputs can tell you whether an aftermarket air intake
has helped or hurt your power output. You can read these sensors
yourself by using an OBD-II scanner, or a cheap electrical multimeter.

You are correct to suspect that most CAI's
only make more noise and have flashy colored parts.

Want confirmation about this from a CAI manufacturer?

Well right now KN Filters is running an advertisement in the various hot rod
magazine saying that a typical paper air filter from the factory creates a
restriction of about 2.8 inches of water....and when this filter gets really
dirty the restriction rises to about 12 inches of water restriction. The KN
advertisement has a dyno graph showing that this can cause about 11 hp power
loss on a high horsepower engine.

The pressure of the air around us is about 404 inches of water
so KN Filter is saying that the pressure is changing from
404 - 2.8 = 401.2
to a new pressure of
404 - 12 = 392 inches of water

Play around with the equations above
and you can find out what the actual horsepower of the engine KN was using
was....and then confirm it by looking at the dyno graph in the advertisement.
=======
Heard of the 'Ram Air' effect where the speed of the air hitting the vehicle
builds up pressure in a forward facing air duct and helps 'supercharge' your
engine a bit. ?

Well, at 'typical' street speeds the effect is very very small.

The formula for that is:

Inches of water pressure from Ram Air = (mph) times (mph) divided by 2025.

So at 70 mph the ram air effect is:
(70 mph) times (70 mph) divided by 2025 = 2.4 inches of water.

So the very best possible air inlet tube designed for Ram Air would actually
have a positive pressure of 2.4 inches of water.

How much pressure is an inch of water ?

One psi of pressure is equal to about 28 inches of water.

You can get this by dividing the cubic inches in one cubic foot ( 12 x 12 x
12 ) by the weight of one cubic foot of water ( 62.4 lbs).

The air pressure around us is averages about 14.5 psi at typical heights above
sea level.

So another way of looking at it is that the air pressure around us is about
400 inches of water. ( 14.5 x 28).

So the best Ram Air system at 70 mph gives you a boost of about 2/400 or one
half of one percent. Small.

Ram air started in airplanes where it means more. An airplane going 300 mph
gets a boost of:

300 x 300 divided by 2025 = 44 inches

This is a percentage boost of 44/400 or about 11%

Want a challenge?
Consider your tires.
Some strange facts:
At 70 mph the center of your tire is moving 70 mph.
The bottom of your tire where it 'grabs' the pavement is moving at 0.1 mph
The top of your tire is moving forward at 140 mph.
If you could put a 'Ram Air' inlet right at the top of the tires (where it is
horribly dirty and wet) you could get a significant air pressure boost.....

Supercuda beat me to it. The challenger t/a hood looks engineered to clear the boundary layer, AAR cuda hood looks like a crude NACA duct, and the old superstock scoops look "engineered" to clear tall manifolds or velocity stacks rather than a ram effect.

Cool air = better than hot air. In fact I'm surprised that after all these years of hotrodding, the standard open element 4 barrel air cleaner sucking in hot under hood air is still the gold standard.

As far as any ram effect goes, even IF you did get a smidge of pressure off it, at best it would help to overcome the resistance of the air filter. The carb is not going to see pressure.

Did a lot of work on this in the old Comp car. Figuring the area of the scoop inlet and where the tipping point was as far as at what speed the scoop was travelling vs the engines inlet demands. At that velocity and higher the engine sees a positive pressure in the scoop. Ram air as it were.

"Some strange facts:
At 70 mph the center of your tire is moving 70 mph.
The bottom of your tire where it 'grabs' the pavement is moving at 0.1 mph
The top of your tire is moving forward at 140 mph."

That point was made here in 2011 with an explanation of Weldon's Vegas Indy car fatality, nobody got it then either.

I have wondered about that too.

When a gasoline engine is idling,
Does it use less gallons in an hour
With hot air?

At idle
Intake side pumping losses are high
Because the throttle is nearly closed.

Hot air has less oxygen per cubic foot than cold air,
So the throttle has to open a bit more
And idle vacuum has to drop,
Therefore more atmospheric pressure is available
To push the piston downward on the intake stroke.
This reduces intake pumping loss.

My 1995 Magnum 5.9 V8 seems to have a complicated fender side air inlet system that sucks hot engine compartment air at idle,
but when the truck is moving gets cooler air from a passage in the fender that has its inlet up by the passenger side headlight.

It is so complicated that it has to be designed that way on purpose.

Since they are using the fender sheet metal as an air passage,
Why didn't the designers get the engine air from a vent high up on the passenger side A pillar. This "snorkle" inlet would have other advantages.