The reality of ram air is that it does work, and is an effective tool for any engine builder or tuner to use to achieve their performance goals. We will cover many areas of ram air system design and function in this discussion but first let's hear what Harold Battes, President of SuperFlow Corporation (this is the company that makes flow benches and dynamometers) and one of the foremost fluid dynamics engineers in the US has to say about it.
Ram air is an attempt to put the induction losses back into the manifold during the cylinder firing process by pre-packing the manifold with air. This will lead to much higher air flow rates in your cylinder heads at lower lift values and will maintain proper manifold pressures and port velocities at higher Rpm during WOT operation under actual road loads above 50 Mph. This allows you 100%, or in the case of the VR-1B, over 100% intake efficiency at only 70-75 Mph depending on the car in question. The VR unit will build and maintain 100% efficiency at only 50-55 Mph. This makes for a much quicker, faster car at speeds that are more usable. Other intakes are struggling to make pressure at this level and require much greater road speed to build pressure if at all.
A properly designed ram air system will increase an intake's CFM, make pressure or even create positive boost. That is boost above 1 atmosphere or 14.696 PSI (this is considered the maximum pressure that most factory atmospheric engines can generate in the manifold without some form of forced induction or unless the motor has been modified; head work, performance cam etc. But as you will find rarely does any motor do this under actual road or track loads. That is a dyno vs. the actual road itself. Most factory intakes are about 80-85% efficient on average. Some, such as the LS1, are closer to 93-95% (depending on the cars year model) from the factory.
Here is where the problem lies. Most people at this point, in order to try and test a system themselves, will simply hook up a boost gauge, drive down the road at WOT and watch as the gauge moves from a negative Psi (usually -14.50) to 0. Then they say that it doesn't work, not taking into account any increases in CFM of the intake system. Let's say they do measure it properly and measure an increase in manifold pressure or boost over stock or even achieve "positive boost" at which point they may see (using the example from Harold Battes) +.176 Psi and say, oh well that's only worth a small amount of Hp, nothing could be further from the truth.
All motors under actual road or track loads will lose pressure in their manifold. This can be anywhere from -.001 Psi to the most that we have seen, -2.0 PSI on a 427 that made over 2 Hp per cubic inch. No matter what type of motor or who built it this will occur. We will expand on this later.
When this occurs, there is a loss of Psi and Cfm as the two are related in that depending on the intake manifold design and the firing of the motor itself you cannot have a Psi increase without a flow or density increase unless you decrease the plenum volume in the intake manifold itself or alter the firing condition of the motor. Some motors fire two cylinders at once, therefore two cylinders must receive a given volume of air at the same time. This makes it harder to make manifold pressure because most manufacturers or engine builders will increase the volume in the manifold or alter the camshaft accordingly to bring in more air but we won't get into that in this discussion.
Psi, Air Density, Flow Rate and Horsepower
All of these effect one another, however, all do not have to be present to make Hp (Psi is not required). First, let's go over what you will need to use to measure manifold pressure. You will need a boost gauge that reads below 1 Psi. Some use a millibar gauge. Others use a laboratory grade electronic manometer that reads as low as .001 Psi. Some of these devices can be configured to read in both values. The reason is simple. You need to be able to measure as low as .001 Psi accurately because you are looking for .10+ changes in manifold pressure and a typical boost gauge will not indicate this for you. A typical boost gauge won't even move unless there are changes of up to 1 Psi, positive or negative.
In any engine as you go to wide open throttle (WOT) pressure is created in your intake manifold. The general assumption is that the motor is breathing or developing 1 atmosphere or 14.696 Psi. The motor, if efficient, will build to 1 atmosphere however this rarely occurs in any motor. What normally occurs is that the motor builds to a given pressure, somewhere below or equal to 1 atmosphere, and then begins to loose pressure under increased load. This loss of pressure is somewhere below 14.696 Psi. These losses of intake PSI are dependent on intake manifold design, camshaft profile, cylinder head design, compression ratio, the Rpm you are turning and the overall heat and frictional losses that occur. Usually on a stock motored 2001 LS1 the pressure loss is about -.75 Psi and it's costing you Hp. A totally stock C5 can be below 1.1 Psi at WOT depending on the year. A Ram Air system is designed to draw or pack that pressure back in to the manifold. Well you say, what's -.75-1.10 Psi really worth? In order to give you this explanation, we will keep it simple but we will have to set up some control parameters. This is for Psi only; we will cover CFM and Air density later.
To factor your gain if using a ram air system, test your car with whatever intake system; stock or modified. Monitor the intake pressure on the dyno to give you your Hp/Psi formula. You may then proceed to road test monitoring the pressure increases if any to determine the true power and overall efficiency of your system.
The day: a textbook 14.696 Psi or 1 atmosphere.
The car: a showroom stock car, no modifications at all.
I will give you an example: a totally stock 2001 6-speed Corvette and a textbook 14.696 PSI day. These are rare but will suffice for this explanation. There will also be some variation from car to car as there are casting irregularities, deviation in cam lobes and overall build differences. This is why some guys get the ringer car and others well...fall a little short. This deviation will show up in the manifold pressures at WOT. So basically use this as a reference. The best way to see how well your intake system works is to dyno your own car whether stock or modified and measure the manifold pressure at peak and then the drop at higher Rpm. This will give you a good base to use these formulas. You must remember that the on-road losses will be greater than the losses on the dyno. Automatic cars will lose more than 6-speed cars due to increased loading in each gear.
WOT=13.946 Psi, that's -.75 Psi, car dynos at 310 Hp at the rear wheels. In other words, your car is losing this pressure under load and it will lose more under actual road and track loads. (For our explanation this will suffice)
The equation is simple. 310 Hp divided by 13.946 = 22.23 Hp/Psi. Remember that the car is -.75 Psi at WOT. So the equation is: 22.23 Hp x .75 = +16.67 Hp increase. Now at this point you are not into positive boost yet. You are only at 1 atmosphere (14.696 Psi). If you have an aftermarket intake system you would simply add the gains that you saw on the dyno to this figure for your total power at that speed and Rpm.
Now let's try a 99 6-speed C5 with its more restrictive factory intake system using the same control for the test.
WOT=13.45 Psi, that is -1.25 Psi, car dynos at 301 rear wheel Hp.
301 Hp divided by 13.45 Psi equals 22.38 Hp/Psi.
22.38 Hp x 1.25 Psi equals 27.98 Hp increase at 1 atmosphere.
A VR achieves this at 50-55 Mph. (Rarely will "any" car lose intake pressure in 1st gear or 0-45 Mph. If so it has very poor intake efficiency.
In both of these tests the cars ram air intake systems returned the motor to 1 atmosphere only, NO positive boost. Positive boost would be any figure above 1 atmosphere or +.176 Psi. This would be 14.696 Psi +.176 Psi = 14.872 Psi (absolute pressure or total pressure). To figure this you can simply use the same Hp/Psi formula:
99 6-speed C5: 22.89 Hp x 1.426 Psi = 32.503 Hp increase @ 14.872 Psi.
At a 12% correction factor from rear wheel Hp to flywheel Hp that would be a 36.403 Hp increase. Cars will vary some what from year to year and weather will affect barometric pressures as well.
The best factory stock manifold reading that we have ever seen on a C5 was on a 02 Z-06 which was -.50psi at WOT in 3rd gear. 4th gear it fell even further. This is why we test on the road only for pressures as it will very from a dyno. The Dyno showed a .50 loss of manifold pressure. This same car pulled 359.7 rear wheel Hp at .50psi below 1 atmosphere. On the road in the same 4th gear as the dyno pull this car's intake pressure fell to 14.01 Psi at WOT. That's .686 Psi below 1 atmosphere with the factory intake system.
An off-the-shelf VR equipped with an Hp filter installed on these cars is worth about 12-14 rear wheel Hp static. This same car pulled 372.1 at the same -.50 Psi static. This gives a Hp/Psi of 26.26.
1st gear = 1 atmosphere (the car will do this stock)
2nd gear = .04 above 1 atmosphere (stock car drops .25psi here) = + 7.62 Hp
3rd gear = .12 above 1 atmosphere (stock car drops .50 psi here) = + 13.13 Hp
4th gear = .10 above 1 atmosphere (stock car drops .69 psi here) = + 18.12 Hp
Now add your dyno improvement of +12-14 Hp to any of these figures for your total power gain at speed. Multiply by a 12% correction factor for flywheel Hp which equates to a best of 34.18 Hp gain on this run. VR-1Bs make torque gains that are equal or greater than their power gains. VRs develop tremendous power under the curve as well. Check out Ram Air and the dyno in this discussion for more information.
This is the car that everyone looks at because it is the fastest factory stock Corvette. But it also gains the least of any of the C5s from this system. Yet all of our customers who have tested the systems on these cars are getting 3.5-4 tenths and 3.5-4.0 Mph through a ¼ mile. Now you see why.
These are the same formulas used for turbocharger design and application under road loads. A turbocharger is rated by its CFM at a given boost level. In our case we need to determine the Hp per Psi ourselves as there is no way to accurately flow an internal combustion engine during actual operation other than one of two ways.
1. Dyno and monitor Hp/Psi levels at each Rpm under load.
2. Dyno and monitor Rpm levels vs. CFM/Hp under load.
The most accurate is #1 and is most widely used in the racing industry. You see CFM must first overcome these same losses to make 1 atmosphere then move on to +1psi. In other words a turbo, when making +1 Psi, is really making +2 or more depending on a certain motor's losses that had to be overcome. This is part of turbo lag. Basically, your engine becomes the turbo or air pump delivering CFM at each given pound per square inch or Psi. CFM increases as does Hp. If the CFM is increased in the intake system it can be caused by an air density change, a flow rate change or both acting together. The second here is usually the case in most systems. A cooler denser air charge will mean that each molecule of air is packed that much tighter allowing for more air in a given area or volume. This air density change will affect flow rate. However, you can also increase the flow rate by the design of the air box itself or by forcing air into it. We will expand on this later.
Now at what type of speeds do you need to be traveling to start to achieve this ram effect or boost back to 1 atmosphere and above? For this you have to look at each given ram air system and intake or vehicle package as a whole. Here is some of what you must consider in any such system.
Scoop Style: A forward facing, NACA, deflecting and cowl.
Forward Facing Location: This is regarded as the most efficient and allows for maximum pressurization with minimal head loss.
Deflection: This would be a scoop located behind a given area that is fed by a deflecting object or winglet. These are very inefficient due to the loss of energy from the deflecting process and the air turbulence that is generated.
NACA: An efficient design but placement is critical. If placed incorrectly, no pressurization will occur. This is why Katech moved the C5-R's inlet to the front screens in the fog light area.
Cowl: These are useless for ram air unless fed by some form of deflecting object. However, they are very good for cold air boxes if designed correctly.
Aerodynamics Leading to the Scoop: A direct shot is best becasue if the air is curved or deflected in any way it will destroy the dynamic pressure that you will need to achieve any boost at all. Head losses in the scoop area or the velocity lost due to scoop design placement or friction, etc.
The System's Overall Design Package: Is it a proper air box? Does it feature properly sized divergents or venturis for the speed and application you have intended it for?
Manifolding: Is the system large enough to support your car static?
Filtration: How much pressure drop is there across the filter? Air must pass through the filter at speed. When this occurs there is a loss of pressure (most cotton-based filters lose from -.75-1.25 Psi). If multipliers are not used leading to the filter; EX: ram tubes, decreasing radius scoops; then all that you will have is a filter hanging in the wind. This may yield some increases in CFM but to build manifold pressure will require a substantial amount of road speed. This is more important than the overall flow rate of the filter being used. What style of filter is it? A panel, a cone or a round filter.
Aerodynamics leading to the filter are very important here, in general you never want to use a cone type of filter in a ram air system (the air must turn into the filter then return back to the intake, this is because of the cotton construction it will simply not flow air at angles). This is why race cars, where possible, use a panel or flat filter. This gives a direct shot with minimal losses to changes in direction, something that air does not like to do. IF a cone must be used a competition foam filter is recommended (you will not find these at the local speed shop but from specialty manufacturers only) as foam can flow air in all directions. Round is good if sealed in a round air box. Example: a carbureted car.
Does the vehicle use an individual intake system per cylinder or does the motor share a common plenum area? This has a great effect on system design.
Filter location: Is the filter located behind any type of multiplying system as talked about above? Or is located at the beginning of the entrance relying solely on vehicle forward motion for added pressure? If the ladder is true it is a filter hanging in the wind as it will simply take too long to build pressure, if at all (100 Mph+).
Sealing: Is the system sealed? This seems redundant but you would be amazed at how many are not or unseal at speed.
Everyday Use: Will it be used everyday or for track use only? What type of power boost are you going to try and make and at what speed? This effects design and packaging.
Displacement of the air ducts and Rpm of the engine are important as they will determine the airspeed in the ducts themselves in order to achieve boost.
What it amounts to is that all motors have pressure losses, so each ram air unit must be engineered for each given application, one type or style may not work on another vehicle. Example: a motorcycle with individual carburetors or throttle bodies requires a plenum, the air box becomes the plenum and pressure from the velocity in the ducts is recovered here. This is referred to as a standard negative venturi system.
Here are some examples of restricted racing systems:
 |
 |
|
 |
||
The VR-1B uses a combination of negative venturis, positive venturis and splitters to achieve an increase in pressure velocity at road speed yielding an increase in manifold pressures and excellent overall efficiency in the intake system that rivals the best racing systems. We know because we build them for racing teams.
This reflects current race car design philosophy as you will see that they now keep the system at the same overall area at the entrance and then open at the last possible moment to maximize the pressure velocity. This is now considered the norm. 5 years ago it was a full negative venturi. Now it's keep it tight and fast to get it through the filter.
How Fast Do You Need To Go?
For this we will use a stock 99 6-speed C5 with its 3.42 axle and equipped with the current VR-1B. Technically you begin to see boost on a 6000 Rpm motor that produces 350 Hp, which is pressure being put or packed back in to the manifold, at around 50 Mph. The pressure created here is small but it is exponential, meaning it will rise by the square of the speed that you are traveling and will depend on the ram air systems design as to its efficiency at each given speed and the Rpm of the motor. An example: at 50 Mph the theoretical pressure rise on the nose of a vehicle is .044 Psi without any multipliers (we will get to this later). Where is your current manifold pressure? Typically at WOT in 2nd gear at this speed it's in the negative by a small margin yet the outside air is above 1 atmosphere by +.044 Psi. Your system's efficiency will determine how much of a benefit you get from this. But in any case it will lead to quicker cylinder filling and quicker acceleration. You must remember that this is exponential so at 100 Mph you would be looking at +.176 Psi above an atmosphere. This again seems small but your goal is to get the system back to 1 atmosphere or more in real world conditions, not on a dyno as the loads and test conditions are different. This is entirely dependent on displacement Vs. Rpm Vs. speed Vs. ram air duct size and design. You have to get all of these correct in order to get the system to function. If the car has an automatic transmission or a highway gear it will affect Rpm, shift recovery speed etc. Ex: if you have an A4 car with 2.73 gear it will achieve 1 atmosphere in 1st gear at 50 Mph. A 3.42 6-speed will be in second gear attempting to build the pressure lost during shift recovery then break 1 atmosphere at 60 Mph. The A4 car has shifted and is now below 1 atmosphere but building quickly. What is happening is that as each car puts a greater load on the motor due to prolonged loads in gears and you will incur more losses. These losses will increase the higher the gear that you are in. If air multipliers are used in the system it will increase pressure X times this amount quite easily. The VR has such a multiplier system in it allowing it to create strong pressurization at relatively low road speeds.
Air Density: Cold Air and Ram Air Power gains
Most people who doubt ram air merely call them cold air intakes delivering a cooler denser air charge to the motor and that is where they achieve there power, not from any CFM flow or Psi increases. Well, it is a combination of CFM and air density caused by lower air temps or altitudes. Once again this is system and application dependant but generally they say (text books) that a 10 degree drop in air temperature is worth about 2 Hp. We like to think of this as a raw number because this application is a street driven LS1 or LS6. We are talking about a Mass Airflow Meter controlled vehicle that will tune or adjust to the weather conditions for you. When in cooler weather the computer will not back the timing out of the motor as quickly and it will richen the car up for you to some degree to take advantage of the added air, basically tuning the car for you. This is worth more than the 2 Hp you are seeing at peak power. It translates into a lot more power under the curve. Air flow rate, air pressure and air density is our priority. If you had to prioritize them in order you would be making a mistake. They all work together.
|
If you are getting an increase in CFM yet no manifold pressure increases then you are still getting some benefit but not as much as you would if you could build some manifold pressure.
The Doubters of Ram Air and the Power Gains that are Possible
Here is an article from that will help to expand on this section:
 |
 |
 |
 |
What it amounts to is that the pressure that starts at ~50 Mph in an inlet area of 57 inches and finishes at 12.3/4 inches is increased by X amount as the vehicle accelerates to whatever given speed. This velocity pressure is then recovered in the plenum of the intake manifold. The plenum's volume and the head losses will determine the decrease in velocity pressures. This is simplified but in this application applicable because we are not referring to a steady condition nor an equal venturi.
Here's some more general information taken from actual on-road readings in the intake manifold and air duct assemblies using a VR:
What you must realize is that the intake air speed on a stock LS1 at WOT is around 48-52 Mph and if the ram air system is efficient, which the VR is and then some, you only need to break these speeds in order to exceed the engine's intake velocity to start ramming more air into the intake system. This is from actual on-road measurements, not a calculation of area and velocity. What is usually missing here is that during shift recovery in any gear above 40 Mph the duct air speed will exceed the engine's air speed and you are still seeing a benefit at even low speeds. What you are also not seeing here is what your intake manifold pressure is vs. outside air pressure. Usually at this point in second gear it is around -.5 Psi vs. the outside air pressure that is at +.04+ Psi above 1 atmosphere. We are talking about a deficit of .54 Psi or just over 1/2 of a Psi. If your intake is 100% efficient then this will result in a gain in manifold pressure at minimal road speeds.
Example 1: When you are driving normally at say 1/4 throttle your intake pressure is -14.50 - -8.50 Psi. When you go to WOT your Rpm will rise. Somewhere in here your engine may reach 100% volumetric efficiency (1 atmosphere) for a short time and as the Rpm will continue to rise. It will fall back to something less than 1 atmosphere unless a ram air or some form of forced induction is used. This will get worse the higher the gear that you are in. All motors do this. Even the best racing engines will lose pressure in there Rpm curve. Racing engines, where allowed, will run a ram air system. These are heavily regulated by the respective sanctioning bodies due to the power that can be produced by these systems.
Example 2: Say that you are traveling at 40 Mph in second gear at 2000 Rpm in a 6-speed C5. The air speed in the throttle body is only 18-20 Mph. Your outside air speed is now exceeding your intake speed by 20-22 Mp. Now nail the throttle! Lot's of torque is what you will see here and added manifold pressure that would normally not occur allowing your motor to rev quicker to redline with no loss of manifold pressure.
Example 3: Now let's say that you are driving through a twisty road and you are in 2nd gear at 40 Mph accelerating up to 3rd gear to say 4800 Rpm and then back down for more turns. At 40 Mph in second you will see lots of torque and no loss of pressure at the top of second and some boost. Once into 3rd gear during shift recovery you will notice lots of added power under the curve. That's because the system has moved enough CFM to start packing the manifold creating some substantial pressures. This is what is so seldom talked about concerning ram air but every racing engineer knows that improved drivability from added torque and power under the curve make for a quicker, faster car that is a lot more fun and easier to drive.
The bottom line is that "ANY" OUTSIDE FORCE that enables your car's manifold to draw back some of its Psi or CFM losses is RAM AIR and is a form of forced induction.
Here is an example of a factory 2002 SS Camaro with a factory ram air system that many say does not work or does nothing because it is not sealed, a poor design etc. You will notice how with the ram air functioning the intake is pressurized sooner BUT DOES NOT INCREASE IN PEAK PRESSURE. And the mass air flow rate is increased by some 20%. It also recovers much quicker during shifts and maintains its flow rate and intake pressure very well. Remember we are talking about a stock factory system down to the paper element filter and it leaks air. If it is sealed it will build pressure.
Here are two runs logged by B&B Electronics' Autotap software. This software is a good tool to use but you will have to monitor the Barometric pressure from an outside gauge because once the ram air system breaks 1 atmosphere it will be reset by the computer to a higher setting because this software was not written to monitor boost, it was written for atmospheric motors only, so it resets the baro to +.13 or +.14 higher than it's last reading. This is also why we use millibar gauges taped directly into the manifold. The first is without the factory ram air system functioning and the second is with it functioning.
Boundary Layers
Although boundary layers do exist on the C5 they are only relevant on certain areas of the car depending on what you are trying to do and the road speed that you are travelling. The C5 is not a wing nor is it an old brick. It is one of the most aerodynamically efficient cars that you can buy with a very small frontal area in terms of air drag. If you measure the boundary layers on the car you would find that rarely do they exceed 3-24 mm total as opposed to an older car were it can be inches let alone a wing were they can approach 1 foot or more just before a stall. For this application we will concentrate on the nose of the car. If measured properly, by properly we mean a full 10ft tall and 10 ft wide stream of air as is generated in a full scale run (a full scale run means that you are testing the entire car for a complete look at the aero package) in a wind tunnel, the area of highest air pressurization is in the fog light area (contrary to popular belief). This area represents over 70% of the nose of the car. If the car in question is running a VR unit then the engine is also creating a negative pressure in this area. Katech is now using this area for the factory C5-R Corvettes for this very reason. They are no longer using the NACA ducts on the hood. According to the head of there motor program, "This was the only area that we could get to build pressure in the manifold." Speedvision World Challenge GT Racing's Rathman Racing is now using the VR system and they are now seeing added manifold pressure and positive boost over there modified Donaldson ram air they were using. The change equates to lower lap times and much needed torque and Hp for shooting off of corners. Katech and Rathman Racing are not the only ones that can benefit from this added power. Now you can have the same added power for your car on the street. On a C5, boundary layers do apply but only to certain areas of the car and at road and some race speeds they are minimal at best.
Ram Air and the Dyno
Cosworth knows that you must blow a sealed force into the air box at a simulated road speed if you are going to try and measure true Hp on a dyno with a ram air system. This dyno can simulate real world conditions as it uses computer telemetry from the race car to construct a simulation on the dyno of each given track and load condition.
In the case of all VR ram air units, true power output will never be able to be measured on a dyno as they are designed on a race track (to be moving). All are tested at varying speeds with multiple multipliers in them in order to function at the desired speed and pressure levels, not noticeable on a static dyno (if you like strong dyno numbers instead of unbelievable on track performance simply disconnect the ram tubes or contact one of our tech staff to find out how to adjust the VR for your power needs). What it comes down to is during the design process you must determine if you are building a ram air system or a system to pull numbers on a dyno. The reason being, each property PULLING or PUSHING, has its own internal aerodynamic package. The VR-1B has a multiplier system in it (this will hurt pulling air flow static, due to there shape, this can be negated by using an extra ½ inch step in front of the filter but then it will delay the ram effect as well). This is similar to a blower drive or turbo multiplier. It is applied to airflow at each given speed. Example: say you had an aftermarket cold air box that at 75 Mph was 90% efficient. The VR is over 100% efficient at that same speed. Now at 100 Mph the cold air is still at 90% (more than likely is has slipped to 88% efficiency, typical of this type of setup). The VR is at well over 100% efficiency and climbing! This is a gain that you will never see on a dyno.
In VR VS the Competition on this site, you will see that our test car was (from our strongest competitor) over 1.5 tenths and 1.7 Mph faster in the ¼ mile. How? All ram air boxes are about the same aren't they?
We love answering this because in the aftermarket it seems that very few ever care to really talk about or emphasize to you the customer that if you want a fast car you need power and torque developed under the curve. Everyone is so concerned about peak power on a dyno that they forget two things:
1. The car needs power under the curve to accelerate.
2. The intake system must be able to recover, build and maintain air pressure as quickly as possible. This means making the intake as efficient as possible NOT at PEAK but during shift recovery under the curve requiring proper air box design and internal systems to increase velocity pressures to help offset any head loss incurred in the system.
As independently dyno tested by Cartek and C5 Super Tuner shootout winner Danny Pop, the VR-1B made anywhere from 2-4 rear wheel Hp more than this competitor at peak but at 5000 Rpm they both saw 5-10 Hp more while sitting on a dyno on stock and modified cars. The VR-1B was designed to perform under the curve. The system will typically gain the same or more torque than Hp depending on the filter used and the year of the car. The ram tubes as evidenced by the graph in VR VS competition, helping the system to build and maintain pressures quicker than our competitors at speed. Take a look:
(the test car is a 98 A4 with 2.73 axle, other than these intakes, car is stock)
Initially the VR is already maintaining +.25 Psi more at this recovery point, in 1.5 seconds the VR is +.34 Psi from its competitor. Now let's talk about Hp differences using the same Hp/Psi formulas as mentioned elsewhere on this page.
This car pulled 299 Hp at -.89 Psi with the competitor and 302 Hp at -.89 Psi with the VR (this car averaged +2-5 Hp under the curve wth the VR depending on the Rpm). This will yield 21.657 Hp/Psi and a 21.874 Hp/Psi respectively. At shift recovery that equates to 303.19 Hp, the VR produced 311.70 Hp. That's a 8.5 Hp difference at just shift recovery from pressure alone, not including any difference on the dyno we will use the lower numbers (2-5 Hp @ 5000 Rpm). That's a 10.5-13.5 Hp difference. 1.5 seconds later there is a +.34 Psi difference, 14.21 = 307.75 Hp vs. 14.55 = 318.27 Hp. Now we are looking at a 10.52 Hp difference from pressure only. Once again you add the dyno difference using the lower number at 5000 Rpm (+2-5 Hp) and you have a 12.52-15.52 Hp difference and we are only at about 80Mph. Now peak Rpm, the last second before 90 Mph. 14.54 = 314.89 Hp vs. 14.74 = 322.36 Hp and now add the dyno difference at peak (+2-4 Hp) 322.36 Hp +2 Hp = 324.36 or a difference of 9.47 Hp. The only problem here is that as speed rose (not shown on the chart) to a typical C5 trap speed the competitor lost -.14 psi (caused by air spillage pointed out elsewhere in this discussion) bringing the VR back to the full +15 Hp over travelling through the ¼ mile traps. If multiplied by a 15% correction factor for an automatic car that would be a +17.25 Hp difference travelling through the ¼ mile (remember the Mph difference of 1.7 Mph).
If you had to put an percentage to it 60-70% of the time in gear a VR is 12-15 Hp stronger and the last 30% its 12-9.2 Hp stronger than its competitors. There's still one problem here. All of this testing has been done with an Hp filter We have two more filters that can be used. The Hp+ and a qualifying filter. Both of these offer increased ram effect due to lower pressure drops and quicker, yes quicker, recovery pressurization and higher absolute pressures. We also have under current R&D the R-model conversion kit. This kit features a heavily altered internal aerodynamic package to aid in quicker pressure recovery and development. In this we think that you can get the how and whys of it. What you have seen however does not show torque peaks as this is also at shift recovery and a VR as mentioned above either makes identical or more torque than power, usually by 2-4 ft-lbs and this test car makes 318 ft-pounds with the competitor and 322 ft-pounds with the VR. You must measure the Psi at this point on the dyno to get a reference but we think that you can get the picture. This is the current area of racing engine development that is being concentrated on. In the old days you used a dyno. These days it's used for general measurement and to run engines in before being installed in the cars. If someone has designed a ram air system on a dyno then it has a 90% chance of not working well at normal road speeds. It will simply take too long to pressurize or the ducting will be to short and air spillage will occur and the pressurization will be nil and all that you will have is a filter hanging in the wind. .
A proper ram air system is a very complex item to make function properly at road speeds below 100 Mph. We spent over 2 years developing the Corvette C5 unit but our parameters were for OEM, not all-out race use. Our competition makes around 28-32 Hp through a 1/4 mile. The VR on a standard C5 or Z06 averages 35-43 Hp (while using a standard Hp filter) through that same 1/4 mile but the VR will make power and torque faster enabling it to be much quicker even on a dyno as conducted by Lingenfelter Performance. "We picked up 5 more Hp at peak over the Donaldson on our basic 390 rear wheel Hp car on or chassis dyno. " Cartek Racing in Garwood, NJ using a VR set up for their cars (1 inch spacer in front of the filter vs. standard 1/2 inch), they were seeing 2-4 Hp more at peak Rpm with a VR-1B but at 5000 Rpm they were seeing as much as 10 Hp more with the VR unit. Here in lies one of the many reasons why the VR is so quick. The system was designed to be adjustable by simply increasing or degreasing the plenum volume to suit a given cars power needs static. This feature combined with the low pressure drop across of our competition air filters allows the system to make more power under the curve and with a very efficient internal duct package it will force feed more air at lower speeds making for a much quicker and faster car.
It's no wonder the guys at Cartek have the fastest head and cam cars in the country. Some of our customers with stroker motors have gained up to 30 Ft-lbs of torque and 18-22 Hp more than a Donaldson. The reason here is simple. Proper air box design engineered to out flow the competition all the way to 700 Bhp or 8000 Rpm!
We hope that you have enjoyed this small look into some of our R&D for the C5 and If you have any questions feel free to E-mail Us.
A lot of companies talk about performance in the automotive aftermarket, but at VaraRam, we guarantee it! We have been doing it for racing teams for years and now we are doing it for you.
-AutoSport Magazine
-Racecar Engineering Magazine
