chuckster

I was in Orlando this weekend and saw 12" Diameter Trees snapped in half and pushed over flat. Roofs were ripped completely off.

All this done with a measly 100mph wind...... I mean face it guys even a slow C5 will hit the trap in a 1/4 mile run well over 100mph..

If that velocity can devastate an entire city then why is it so hard to believe that that same wind can actually give a 350CI Motor more HP? Even the 2 small openings in the nose will certainly realize a significant pressure increase at that velocity..

ArKay99

with Chuck. My sotp meter agrees also. Too bad there is that little thin piece of paper in there to cut down on the pressure.

Got uid0

"quote kewlbreze"

Dispelling the Myth of "Ram Air" Effect
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.

SIMPLE EXPLANATION

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.

DEEPER EXPLANATION

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.

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.

Conclusion

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.

As a vortex "rammer" owner, I love it the products bang for buck. This is not to single out any one product, as all that use the word "ram" are misrepresenting it.



[Modified by kewlbrz, 11:33 AM 7/5/2002]

dekidex

What is up with that post?? Made me wanna kick my self in the head while running backwards!

OK we get it RAM AIR is a myth!!!who ever wrote all that must have been mad at the world or something while writing it!

OK BUT WAIT THERE"S MORE!!!!

RAM AIR IS A MYTH!!!!

LS1MASACRE

you missed 1 thing, Ram Air is a myth

MTV

Yada, yada, yada and I'm as happy as can be with my Ram Air Myth!

BadBeagle

It was as if someone needed a 1 page report to be 3 pages so they added a ton of filler words.

TomT

After the first 2 lines I stopped reading the "myth" part, but damn I sure was impressed with the volume of the thing.

chuckster

Yeah Really...I have said this 100 times.. But truthfully All ANYONE would have to do to prove that the VRAM works at Speed is the following..

1. Strap Car to Dyno
2. Mount 2 100mph + Leaf Blowers to each Vram Opening. Some airtight could be fashioned to the intakes..
3. Dyno Car With Blowers and without...

If there Proves to be Zero Gain then I will believe it..


For the record.. The Vram does not Gain HP by COMPRESSING the Air.. IE the Definition of (RAM AIR) Very Bad term to use.

It is a Velocity Enhancer. Meaning the engine does not need to "Suck or Pull" the air into the motor at those speeds. Meaning the engine Works less because the parasitic loss is minimized.

The air is traveling so fast at that point that the Cylinders basically fill up on their own instantaneously. That is it... Period.. And it seems so HARD for the naysayers to actually believe this simple penomenon can actually increase HP by 10 or 15...on a 350+ HP motor..

But they believe that a bigger MAF will give it to them

J-Rod

First off there are a couple of things that happen in a hurricane. The ground gets saturated and soft, so trees fall over since the ground they are in soft ground. Take further into account that the top of the tree is like a long lever. The taller it is, the more force exerted. If memory serves me correctly air pressure at 100MPH is ~45 lbs per sq ft. Multiply that by a long lever, and a some fairly brittle wood (like pine) and you get broke trees. Also, in a hurrican you have to look at wind gusts, microbursts, and small tornadoes all of which generate wind velocity much hihger than the 100MPH you cited.


As for the VR. We run one on Tommy's car. The one thing I do know is the foam airfilter in the VR is a huge restiction and removing it was worth several HP as it doesn't have sufficent surface area.

I run a stock airbox on my car. I have tested my car against other cars on the dyno and seen no gain. I have hold roll on races with a VR equipped car, and I pulled him from a roll vs my stock car.

I don't think a hurricane proves anything about a VR... Other than both a hurricane and a VR both end up costing folks a lot of money.

Mr. Lucky

knowledgefreak: Yes, the rest of know how to Google too.

RWhite

http://www.vetteguru.com/ramair/

Mr. Lucky

Is there a point to this... other than boosting your post count? The link you provided is the very first listing on the Google page that I posted.

Operations

This is one funny post, I'm still cracking up.

chuckster

Good point, I was hoping someone had the pressure values at 100mph.. So assuming the each opening on the Vran is about a 1/2 square foot. Then both would be 1 square foot which = 45LBs of Air being forced into the opening at 100mph.. Hmmm

As far as your buddy that you beat.. My guess is he sucks as a driver.. I have seen your ET Posts Jrod.. You are Godlike in what you can pull fron a stock C5.. I'd love for you to drive my car just so it can see 11's!!

Anyway, I digress.... You buddys Vram most likely was lean as hell at the top end and was getting enough K/R to defeat the gains he was looking for.. I had to add significant fuel to my tune to account for a 4th gear lean condition at high speed. A condition that would never be seen on a Dyno Tune.. Trust me.. Anyone who has logged a high speed run with a Vram can see it.

Kind of like putting a supercharger on and forgetting to add more fuel during boost...

Even after it's tuned perfectly... We are only talking about another possible 10 to 15hp more.. This is Trivial in the grand scheme of things for a 350+ HP motor... so my guess is you beat him on skills alone.. You'd even probably beat him if you switched cars..

SmokeyTirez

Man, now THAT would be a site at the track...

The Batman

It wasn't just the speed of the wind that caused a lot of that damage, it was the pressure difference that the wind speed induced.

Take an airplane wing, it's the difference in air pressure that pulls the wing up. Air isn't compressed under the wing, the pressure above the wing is lessened and the wing gets sucked up.

Ask anyone in the flying roof club. It doesn't take a lot of speed to suck an unlocked roof off the car.

StanChampion

Kewlbreze was a regular poster here on the forum and a few years ago this topic was debated to DEATH. So people who have been here awhile will remember this that is all. I probably would have dug up that same post as well. He also taught alot of people about the MAF translator and such.

Just like the Halltech TRIC hydrolock debates that raged and raged and raged

runamuk

chuckster

Great Analogy!! Exactly! The air is NOT Compressed. this is why I believe VRAM needs to change the Terminology.. Because it is NOT RAM air.. But it still Works. Because of the Velocity/Pressure exceeds the vacuum of the motor trying to Pull it in.. By eliminating the pumping loss you have effectively "Freed" up the additional HP. NOT CREATED IT.

Anyway... Here is a great article of a similar test on a Sport Bike. The test I discussed in the beginning using Leaf Blowers on the Dyno..

Also notice the type of Pressure readings they got with the 2 tiny openings on the Bike. I'd bet our big nostrils gain more at lower speeds..

http://www.sportrider.com/tech/146_9508_ram/

RAM AIR: What's It Worth?

By Jon Doran
Photography: Kevin Wing, Jon Doran


Why are Kawasakis so damn fast? Anyone who's experienced the giggling hard-core buzz of a ZX's awesome acceleration from the pilot's seat comes away shaking his head in disbelief. Time after time the big K's machines run faster at the strip than rivals which put out notionally identical horsepower. So where do the extra horses come from? This is an account of the first attempt to scientifically measure the real effect of ram air. The results may surprise you.

WHO HAS IT?


The ZX-11, ZX-9R, later versions of the ZX-6 and ZX-7 and the new ZX-6R Ninja all utilize the ram-air system, and now Honda's latest CBR600F3 has followed along the same path-a sure sign that it works.
The difficulty is in measuring the effect, simulating the results of a 150-mph airflow, while the motorcycle is harnessed to a static dyno. But that is exactly what we set out to do with the help of Steve Burns, noted builder of very special turbocharged, trick-framed motorcycles, sometime dragracer, endurance-racing-team boss and the owner of a Dynojet Model 100 dyno. As an innocent patient we had one meticulously prepared Kawasaki ZX-9R Ninja.

THE THEORY

In essence, the theory behind forced-induction systems like Kawasaki's is quite simple and not that far removed from turbocharging, just at a less extreme level. A motorcycle traveling at high speed is pushing a slug of pressurized air ahead of it. If an air inlet is placed in the correct place, then air entering the airbox will be at greater than atmospheric pressure. The resulting intake charge will be denser and cooler and contain more oxygen and fuel, thus causing a bigger bang and hence-Hallelujah!-more power.

There are limitations. The amount of mixture you can force through a motor is finite. Imagine strapping a ZX-9R on top of a jet aircraft and starting the motor; the plane will rapidly reach a velocity where the motor would be incapable of utilizing the volume of mixture being forced into it. Next, at very high speeds-over say 150 mph, where theory says that ram air should be working most effectively-the nature of air drag means that large increases in horsepower are needed to produce relatively small increases in speed. Finally, compared to a turbocharging system, the increases in pressure are quite low. How low? Before we began testing, Burns predicted, "I don't think we can get more than one psi in there."

THE ZX-9R SYSTEM

Kawasaki's ZX-9R uses a relatively straightforward system compared to the 1995 Honda CBR600F3. Twin vents mounted beneath the headlight channel air via ducts running over the frame beams and into a sealed airbox. Look closely, and you can see two smaller nozzles behind the grilles which connect to the carburetor float bowls. Their function is to equalize the pressure between float bowls and airbox; without them the higher pressure of the incoming charge would upset the carburetion, potentially blowing fuel out of the bowls and tending to push fuel back down the jets, causing mixture leanness. Kawasaki uses much the same system in all its ram-air machines, though the ZX-7 and earlier ZX-11s have a single inlet only.

MEASURING

To reproduce the effects of high-speed running on a static dyno, Burns' intention was to use a fan capable of producing relatively small volumes of air, but at high pressure. The fan was connected via custom-made tubing and coupling to the intake vents of the big Kawasaki. The joint was carefully sealed with high-density foam.

So we could measure the pressures generated in the airbox as we pumped air up the ZX-9R's nostrils, a manometer, or pressure gauge, was plumbed into it. With the manometer we would be able to measure pressure up to 30 millibars above atmospheric pressure. A bar is roughly equivalent to atmospheric pressure; one millibar (mb) is just one thousandth-0.001-of a bar. Not a lot compared to tire pressures, but Steve's experience with varying boost levels on his 250-bhp turbo-which churns out approximately an extra five horsepower for every 70-millibar (one-psi) increase in boost or intake pressure-suggested that if it were possible to create one psi of pressure in the airbox, we could be looking at an increase of 5 to 6 bhp. Note that pressure, in the context of this article, is pressure above atmospheric pressure.

TESTING THEORY

The ZX-9 runs air from the fairing's leading edge over the frame spars.
Other bikes, such as the ZX-6R, pass the fresh-air runners through the frame, while Honda's CBR600F3 breathes in fresh air from above the radiator and below the triple clamp.



Burns' first thought was to set the air pressure at a certain level, say 15mb, and then measure the power at a steady throttle at 1000-rpm intervals. This was abandoned when we realized the results would be meaningless using CV carbs, which wouldn't necessarily be at full lift.

The second problem was that as the slides lift and the motor drags in air, the pressure in the box drops off. Observation suggested that if the airbox pressure was set to 10mb at idle, then at the redline, the manometer would show just 4mb. Obviously this bears little relation to real life, as the only way the airbox would be pressurized at idle would be if the bike were freewheeling down the highway.

Most importantly, the level of intake pressure on the road would be relative to the velocity of the motorcycle. If the airbox were pressurized to 20mb at 150 mph, it would be correspondingly less pressurized at 120 mph and still less at 70 mph. We had no way of reproducing this effect on the dyno, but if we could show that an air pressure of, say, 20mb gave a boost of 3 bhp at a certain point in the rev range and could then relate that to real road conditions, we'd have a fair idea of what the actual power output on the road would be.

In the longer term, Burns hopes to be able to use an interface between fan and dyno to take account of increasing air speed and thus simulate the effect of road speed on a static dyno.

FIRST TEST

The initial step was to run the Kawasaki at atmospheric pressure-no boost-to get a baseline figure. The ZX-9R, like others tested on the same facility, gave 123 bhp at its power peak. The induction fan was then connected, and the bike was run with the intake pressure set to 10mb at idle. The process was then repeated with 20 and 30mb of pressure. In each case the intake pressure fell by approximately 6mb at peak revs when the slides were fully up and the engine was gulping down great gobs of mixture.

The results were gratifyingly clear. At peak power the ZX-9R was producing an extra 2.6 bhp for every extra 10mb of pressure fed into it by the fan. Peak power was up from 123 bhp to 131 bhp, an extra 8 bhp over atmospheric pressure. A secondary bonus was that the bike also hung on to its peak better, which would translate into a more forgiving motor on the road, which would be less sensitive to gearing and thus more likely to be able to take advantage of following winds or favorable gradients to give a higher maximum speed. Because of the testing procedure we'd been forced to use, the graphs also showed similar increases right through the rev range, but this was obviously deceptive. There was no way that the levels of boost measured at low speed on the dyno could be reproduced on the road. At this point we suspected that boost would be insignificant at speeds below 100 mph.

INTERIM CONCLUSIONS

So far so good. The first part of the experiment was a success. We'd shown that pressurizing the ZX-9R's airbox definitely produced power increases. We'd established that the system has the potential to work, but what we didn't yet know was how the pressures we'd managed to generate on the dyno-a maximum of 30mb at idle, or 24mb at peak revs-related to real road conditions. Phase two was to attempt to establish what sort of pressures are actually generated in the Kawasaki's intake system at speed and relate them to the dyno results.

Hidden but visible behind the black aluminum nets are the twin-snorkle balance pipes, which pressurize the carb float bowls to match the airbox.
To reproduce the effect of a rapidly moving ZX-9, we pumped air up the Nine's nose with this attachment; the lower hose is the standard dyno cooling hose directed at the radiator. For an airtight fit, Steve Burns taped the intake hose in place and checked the pressure with a manometer.
Motorcycle (Kawasaki ZX-9) speed and airbox pressure



PHASE TWO

Had we been NASA or a top GP team, the next step would have been easy. Strap a datalogger to the bike, rent a private test strip and go play for a couple of days. We weren't, so the manometer was cunningly strapped to the gas tank, green food coloring added to the fluid for added visibility, and a portable datalogger-yours truly-mounted to the bars.

Just riding from the dyno facility to the strip was illuminating. We'd reckoned on needing 90 mph before boost would register, but at an indicated 70 mph the manometer already showed 8mb of boost.

At the strip we were able to give the big Kwakker its head, with one eye on the slowly rising column of green fluid and the other on the rapidly rising speedo. At the end of each run we logged boost pressure against indicated speed.

The results were even better than we'd hoped for. At lower speeds (under 120 mph) the gauge was easy to read and the results quite consistent: at 70 mph pressure was 8mb; at 80 mph, 10mb; at 100 mph, 12mb; at 110 mph, 14mb. From this point things really took off: At 120 mph (indicated) the airbox pressure was approximately 19mb, at 130 mph about 23mb, at 140 mph, 26mb and at an indicated 150 mph, the gauge was beginning to pump out green liquid as it bubbled over the 30mb limit.

At a real speed of 167 mph, past experience shows that the ZX-9R's speedo indicates 181 mph; there was obviously even more to come, perhaps as much as 30 mph worth of additional air pressure. Plotting the air pressure figures against speed for a rough representation of the way the air pressure increases suggests that the progression isn't linear.

This is as we'd expected. Air drag doesn't increase at a linear rate but relative to the square of the speed. At above 25 mph, air resistance builds in proportion to the square of the air speed over the motorcycle: twice the speed, four times the resistance. The faster the bike goes, the greater should be the increase in pressure and thus intake pressure. When we plotted the rough course of the pressure increase on a graph and continued it upward, we came up with a projected 44mb (or more) of pressure at an indicated 180 mph, when the bike would actually be traveling at its real top speed of 167 mph.

SO WHAT DOES IT MEAN?

The maximum pressure we were able to generate on the dyno was approximately 30mb, which gave a peak of 131 bhp from a ZX-9R as compared to the 123 bhp measured at rest. In other words, each 10mb increase in inlet pressure is worth approximately 2.6 bhp at peak on a derestricted 9R.

At an indicated 150 mph on the road, the inlet pressure had already neared the 30mb figure. We can therefore say with confidence that the ZX-9R is producing at least 131 bhp at the rear wheel in real world conditions-8 bhp more than at rest on the dyno.

Flat out, however, the Ninja indicates another 30 mph on the speedo. If boost at this speed was, as seems likely, 40mb, then the gain over atmospheric pressure would be approximately 11.5 bhp, giving a peak figure of 134.5 bhp. If inlet pressure reached 45mb, which it might well do, then the increase would be as much as 12 bhp, or a peak of 135 bhp. In other words, 123 bhp measured normally on a static Dynojet rolling road dynamometer could translate to as much as 135 bhp or more on the street. Ram air works.

IMPLICATIONS

The manometer wasn't eye-pleasing once taped in place, but it worked well, measuring pressure in the airbox at simulated speeds up to 150 mph. This pressure gauge allowed us to quantify the effect of Kawasaki's ram-air system in the real world.
Kawasaki ZX-11 D ram-air intake system.
This magnification of the dyno chart shows the difference between dynoing a ZX-9 with ambient pressure (lower line) and then stuffing 30 millibars of wind into the intake system-a gain of eight horsepower (from 123 to 131 at the peak). The manometer shows that the ZX-9 reaches 30 millibars of airbox pressure at 150 mph.



An extra 12 bhp sounds like an extraordinary power gain for nothing except a bit of wind, but it's important to remember that at lower speeds the increases won't be as significant. Up to 120 mph when the boost hits 20mb, we're only talking about the odd bhp. From then on it gets progressively stronger. As the effect is speed relative, it's at its most pronounced at very high velocities; the faster you go, the stronger the boost. But, hey, how many of you ride at 150 mph on the street? Never mind, don't answer that.

Having said that, the effects of even small amounts of boost on throttle response haven't really been investigated and may help to explain some of the surging acceleration typical of big Kawasakis.

It does, however, clarify the impressive figures that Kawasakis deliver at the strip and explain why a ZX-7 putting out the same power as a GSX-R on a static dyno will romp away under speed testing. It also begs the question of when someone is going to bring out a fully functional aftermarket pressurized-intake system.

Finally, it explains why Honda's jewellike CBR600 has finally gone the ram-air route in its quest to head off the ZX-6R.

This story was originally published in the August 1995 issue of Sport Rider.