View Full Version : Myths: Electric Turbos and Ram Air. by Conrad_Turbo

12-01-2004, 11:13 PM
By Conrad


fans are not designed for creating positive pressure! they can only put out 5 to 6 in H20 (.18-.22psi). they are designed to move air from one location to another not to pressurize it.

okay lets go with a 2001 celica gts for comparison.

Displacement: 1.8 liters (1,796 cc)
Bore x Stroke: 82.0 mm x 85.0 mm
Compression ratio: 11.5:1
Horsepower: 180 hp @ 7,600 rpm
Torque: 130 lb.-ft. @ 6,800 rpm

okay now that we have the specs of the motor. lets see how much air it consumes.

v = (pi/4)*(bore)^2*(stroke)*(Ncylce)*(# Cylinders)
v = 3.14/4*(3.228in)^2*(3.346in)*(7600/2)*(4)
v = 416369in^3/min(1ft^3/1728ft^3)
v = 241.0 cfm

mind you this is 100% ve. so say at a more reasonable 90% (vvti helps increase this number thus creating more power) so that leaves us with:

v = 241.0cfm * 0.9
v = 216.9 cfm actual

now i am sure you are thinking that the fan is forcing the extra cfm into the motor right? wrong. the air will actually just pass through the blades in a reverse direction thus providing no benefit to power. but this is the thermodynamic method of finding the power a fan needs to move and slightly compress air (between 0.18-.22psi). but lets say it will magically create 5 psi boost for a "30hp" gain.

Fan air power = w * Ht
Fan air power = (216.9cfm)*(5psi)*(144in^3/1ft^2)(1hp/33000ftlb/min)
Fan air power = 4.7 Hp

okay and a 4.7hp = 3.5kw of power.
divide that by 13 volts (average operating battery voltage). now that leaves you with 270 amps of power. so now it leaves you to wonder if you would need a 270 amp inline fuse for this monster fan. i have yet to see anything with a 270 amp fuse in a car. mind you this is with 100% efficient motor as well. so it would actually have to consume more power than that. but oh wait....the factory rating on most alternators are around 80-90 amps (i am just going with an approx value). oh something seems wrong....seems this electric turbo is consuming 3 times as much as the alternator can put out. hmm....odd.

so long story short an electric turbo just won't create more power than what they consume to run them.


Operating Conditions
temperature = Tair = 20C = 293K
atm. pressure = Pair = 14.7PSIA
Cpair = 1005J/KgK
K = 1.4
the Cpair and K are constants for air.

Case 1 @ 100Kmh (62Mph) = 27.78m/s

Calculating temperature of the ram air

Tramair = ((Vcar^2/2gc)/cp) + Tair
Tramair = (((27.78m/s)^2/2(1kgm/Ns^2)/1005J/kg) + 293K
Tramair = 293.4K

the temperature increased by 0.4K or 0.4C.

Pram = Pair (Tram/Tair)^(k/(k-1))
Pram = 14.7PSIA (293.4K/293K)^(1.4/(1.4-1))
Pram = 14.75PSIA - 14.7PSIA
Pram = 0.05PSIG (gauge pressure)

so as you can see driving 100kmh will only have a gain of 0.05 psi! now lets try for 200kmh.

Case 2 @ 200Kmh (124Mph) = 55.5m/s

Calculating temperature of the ram air

Tramair = ((Vcar^2/2gc)/cp) + Tair
Tramair = (((55.5m/s)^2/2(1kgm/Ns^2)/1005J/kg) + 293K
Tramair = 294.5K

the temperature increased by 1.5K or 1.5C.

Pram = Pair (Tram/Tair)^(k/(k-1))
Pram = 14.7PSIA (294.5K/293K)^(1.4/(1.4-1))
Pram = 14.97PSIA - 14.7PSIA
Pram = 0.27PSIG (gauge pressure)

so by seeing how the velocity of the car increases the ram air effect...it is barely anything! so i would conclude that ram air doesn't benefit by actually bulding up pressure but by the fact it is getting a cool atmosphere air.

email me at catchya@shaw if you would like a ram air calculator program that you can use to figure out the ram air effect that you can enter in your own values.

Adrian Avgerinos
12-02-2004, 06:33 PM
To add more information, this website has a VERY good article on the myths of "ramair" induction:


Dispelling the Myth about "Ram Air" in Automobiles

There are many air intakes on the market today. Many claim "superior" performance over others.

Air intakes can be seperated into specific catagories:

- Those that take in warm engine bay air
- Those that are exposed to cooler/fresher air from the front.

The biggest bennefit of adding an aftermarket air intake is unshrouding the factory air box.

The last bennefit is exposing it to fresh air.

Ram Air is a myth, and many intake manufactures use the word Ram Air strictly for propaganda. They also try to show track results compared to other intakes that simply incur too many variables to make a meaningful and empirical determination. 60 foot times, atmospheric changes, shifting, etc, etc. So do not beleive anything you hear regarding such claims regarding air intakes.

Lets take a look at the "Ram Air" Myth in automobiles:

The Ram Air Myth by Dave Rodabaugh

The Ram Air Myth is the most mythical of them all. It differs from the other myths, in that the other myths are misinterpretations of physical phenomena, whereas ram air simply does not exist.

MYTH: Use of a scoop on the front of the vehicle to collect intake air, or provide “ram air” can raise engine performance.

TRUTH: At automobile velocities, there is no ram air effect.


The "Truth" statement says it all. How much simpler can it be? The Ram Air effect is a total myth because it simply does not exist. “But Pontiac uses it on the Trans Am, and they know more than you do.” To those who offer this, tsk tsk. Careful reading of Pontiac’s statements on the matter reveal that the HP increase of the WS6 package are a result of a less restrictive intake, and a freer-flowing exhaust, NOT any ram air effect.

So why does Pontiac use Ram Air? Easy! To make people buy their cars! And they are quite effective with this strategy.


Of all of the applied sciences, fluid mechanics is among the most difficult for many people to comprehend. It is a relatively youthful applied science as well, meaning that it has not had two or three centuries of work to mature into an applied science on par, with say, chemical combustion. To make matters worse, it is mathematically defined almost entirely by experimentally-determined mathematics.

This last point is the true differentiator between those who only understand concepts, and those who can quantify what they are discussing. Truly, quantification is the real skill of the engineer. It is one thing to speak about qualitative issues (the “what” of the physical sciences); it is entirely another to quantify them (the “how much” and “to what extent” of the same). In grade school, students are first taught about “closed form mathematics” and then that these mathematics are typical of scientific expression. A good example of this is Newton’s famed “law of action and reaction”, the mathematical expression of which is a succinct F=MA. So straightforward. So simple. Three variables in perfectly-defined harmony. Given any two of them, the third is easy to nail down.

Unfortunately, a vast, vast majority of the mathematics used in engineering are NOT closed form. Instead, they are multi-variable correlations valid only for a narrow set of circumstances. Deviate from those narrow circumstances, and a new expression must be experimentally derived. Fluid mechanics is almost entirely defined by these experimentally-determined expressions, further muddying an applied science not well understood.

And if there ever were an applied science for which common sense is wholly inappropriate, it is fluid mechanics. Virtually nothing obeys the “common sense” rules of observation, explaining why those who believe in ram air have extreme difficulty in believing that is simply does not exist.

The Deeper Explanation begins with a basic explanation of engine principles. Air and fuel must be combusted at a specific ratio, namely, 14.7 parts air to 1 part fuel (this is a chemical ratio). Stuffing more fuel into the cylinders without increasing the amount of air they also swallow will get no gain whatsoever. So the hot rodder’s adage “more air = more power” is proven correct. Figure out a way to stuff more air into the cylinder at any given RPM and throttle setting, and you can burn more fuel. Since burning fuel is what makes power, more air truly does create more power.

The amount of air which is inducted into a cylinder is a function of the air’s density. As the air flows through the intake tract, it loses pressure, and as the pressure decreases, so does the air’s density. (Denisty is mass divided by volume. Since cylinders are a fixed volume, increasing the density will also increase the mass of the air in the cylinder.) There are two ways to increase the pressure and density of the air inducted into the cylinders:

- Decrease the pressure drop from the throttle plate to the cylinders

- Increase the starting pressure at the throttle plate.

Ram air is an attempt to do the second. Under normal circumstances, the air at the throttle plate is at atmospheric pressure, and this pressure drops until the air reaches the cylinders. Ram air would start the process at some pressure higher than atmospheric, and even though the drop is the same, the cylinder pressure is higher because of the increase at the start.

Just how would this increase in pressure at the throttle plate occur? The oft-wrong “common sense” says, “If a scoop is placed in the airstream flowing around the vehicle, the velocity of the air ‘rams’ the air into the scoop, thus increasing the pressure.”

Why is this incorrect? There are two types of pressure: static and dynamic. Placing of one’s hand in front of a fan, or out of a moving car’s window, clearly exerts a force on the hand as the air diverts its path to flow around it. Most people would say “See? This is a clear indication that ram air works. Clearly there is pressure from the velocity of the air.” Well, this is correct, but only to a point. This is an example of dynamic pressure, or the force any moving fluid exerts upon obstacles in its path as the gas is diverted around the obstacle.

What an engine needs is static pressure. This is the pressure the same fluid exerts on any vessel containing it at rest. For those who were physics/chemistry geeks, it is the pressure caused by the force of the molecules bouncing off of the walls of the container. The key to understanding the difference between static and dynamic pressure lies in the velocity of the gas. Dynamic pressure is only a momentum effect due to the bulk motion of the fluid around an obstacle. Static pressure is an intrinsic property of a gas or fluid just because the molecules of the fluid are moving around. Any fluid which is moving can have BOTH dynamic and static pressure, but a fluid at rest only has static pressure.

The point of ram air would be to increase the static pressure, which would correspond to an increase in the in-cylinder air density, and of course, more air. Superchargers and turbochargers do what the mythical ram air purports to do. A supercharger trades the power of the belt and uses it to compress the air in the intake tract. This energy trade-off results in an increase in intake air pressure, more air in the cylinders, more fuel burned, and more power. A turbocharger trades the power of the hot gases and uses it to compress the air in the intake. The overall effect is the same – an increase in intake static pressure.

For ram air to work, it would have to trade the energy of the air’s velocity (as the vehicle moves through the air) for an increase in static pressure (since static pressure is a part of a gas’s internal energy, we see this is TRULY a trade in kinetic energy for an increase in internal energy). Now for the true reasons why ram air is a myth:

- The way for air velocity to be traded for an increase in static pressure is to actually SLOW IT DOWN in a nozzle of some sort. This is easily the MOST counterintuitive part of fluid mechanics for most people. The “common sense” mind says “In order to increase the pressure of the intake, the velocity of the air needs to be increased, just as increasing the speed of a fan exerts more force upon the hand.” Not only does this confuse dynamic with static pressure, but is also misses the point, which is to trade the kinetic energy of the gas for an increase in internal energy. How can this trade occur if the kinetic energy of the gas is increased? It cannot, and in fact, the only way to trade it is to use the velocity of the gas to compress itself – by slowing it down.

- Below about Mach 0.5 (or about half the speed of sound), air is considered “incompressible”. That is, even if the correct nozzle is selected, and the air is slowed down (the official term is “stagnated”) there will be zero trade. No kinetic energy will be traded in as work capable of compressing the air. The reasons for this are not discussed here; the reader may consult any reputable fluid mechanics textbook for confirmation of this fact. In plain English, a car is just too slow for ram air to work.

Still not enough evidence? Here is a little test. For ram air to work, the nozzle must be of a specific shape. The “Holley Scoop” for the Fiero is the wrong shape, by the way. The fact that it has no net shape at all immediately means it cannot effect any kind of energy trade off, so it cannot possibly create ram air. This is also true for the hood scoops on the Pontiac Firebird WS6 package as well, by the way.


copyright 2002 www.vetteguru.com

continued below

Adrian Avgerinos
12-02-2004, 06:33 PM

What shape must it be? There are two kinds of nozzles. Pick one:

- Converging. This nozzle gets smaller as the air flows through it. It has a smaller exit than entrance. If the nozzle were a cone, the fat end is where the air would enter, and the narrow end is where it would exit.

- Diverging. This nozzle is opposite the other; it gets bigger as the air flows through it. With a larger exit than entrance, the narrow end of the cone is where the air would enter, and the fat end is where it would exit.

So, which is it?

Without hesitation, most of the “common sense” crowd will answer “Converging.” BZZZZT! Thank you for playing anyway! We have some lovely parting gifts for you! Bill, tell ‘em what they’ve won….

The answer is “divergent”. Yes, the nozzle would have to shaped so that the skinny end is pointed into the air stream, and the fat end connects to the throttle plate. How can this be right? Remember, to increase the static pressure of the intake air (which is the true “ram air” effect), the kinetic energy of the air must be traded to compress the air. This is done by slowing the air down, or stagnating it, and the only way to do this is with a diverging nozzle. Ah, but since air is incompressible at automobile speeds, it doesn’t matter any way.


Ram air is a myth because it does not exist, for the following reasons:

- Air is incompressible at any automobile speed., meaning that the kinetic energy of the air cannot be used to compress the air and raise the static pressure.

- The “ram air” nozzles commonly employed on automobiles tend to be the wrong shape. A divergent nozzle is required for ram air. Straight-profile scoops cannot provide a ram air effect.

Select one of the two types of intakes, warm air, or cold air. Beyond that its just about looks.

12-02-2004, 11:44 PM
chris you should probably update with the following info :


12-03-2004, 07:14 AM
chris you should probably update with the following info :

Ya that's just an electric powered supercharger, but still not as efficient as a true supercharger. It's not a typical hairdryer fan configuration as what is mostly sold on e-bay.

12-03-2004, 07:35 PM
cant you get a normal supercharger for about that price?

12-03-2004, 08:08 PM
yes but the advantage is that you never have to screw with your belt/drive system for this kit.

you can install this on a kia. I bet you there are no kits for kias.

you can install this on an elantra. I bet you it's very hard to find a kit for an elantra.

By making this, he has owned the 'all the other cars' segment of the market. which, with the increasing popularity of motorsports is probably becoming a larger sector of the industry.

only 25,000 3000GT vr4's were ever sold in the US.
I think toyota pumps out more corollas in one day than mitsubishi sold 3000gt's or toyota sold supras in a 10 year run

HUGE market.

What's nice to note is that the original post calculates at least ~5hp to make 5psi. If you look at the setup he's using 18hp worth of motors to make the boost.

This exactly the same kind of loss you'd experience if you had a traditional SC which is what they talk about when they talk about superchargers...

ie a traditional sc at the same boost level would make about 18hp less than the figures he's posting on his page because this 18hp comes from the battery, not from your power delivery ...

if this were out back in the day , it may have been on my celica. With the 5sfe's low redline and the fe head design a supercharger makes ALOT of sense

5sfe + bolt ons + SC would make a really spirited daily