dyno results

[Jonathan]

the straps wont make squat difference.....i ran a dyno jet for a while and the numbers were always consistant from 2-4 straps ect.

 

[Yardie]

You're cramping my style homie :laugh:.

 

[ntinhri]

No other shop/tuner in Eastern Virginia can offer its customer with the type of service or capability that we can because of our

Dynapack Chassis Dynamometer. The dyno is not just a tuning tool but a diagnostic tool as well. We've been able to find problems with certain area of the cars power band that customers weren't able to feel on the road, at the track or read on any inertia dyno. Our dyno allows us to tune for a smoother torque band therefore a faster smoother car on the track or the road.
What makes our dyno different from all the conventional roller dynos? The first and most obvious difference is the elimination of the tire to roller interface on a conventional roller dyno. The Dynapack eliminates this variable by using a hub adapter that provides a direct coupling to our Power Absorption Units. There can be no tire slip, no rolling resistance, and no chance of the vehicle coming off of the dyno at high speeds. Most roller dynos use ratcheting

tie-down straps to attempt to hold the vehicle in position while being tested. If the straps are cinched down tightly, the tire has become loaded even further, in an unpredictable manner. While this may be good for enhancing traction, it changes the rolling resistance of the tire - skewing the data further. Since these tie-down straps aren't perfect, the vehicle squirms around on the rollers - dramatically changing the tire drag during the run. If the vehicle is tested in two different sessions, the straps can't be set exactly the same way twice in a row. There have been cases where the ratcheting tie-down straps were loosened by two clicks and the measured power increased by ten horsepower. What if the straps stretches - either from run to run, or during the run itself? Dynapack eliminates these problems.

Even though we specialize in Honda and Nissans, bring your domestic car in to be tested on our Dynapack!​

 

[ntinhri]

i only go off what I read.

 

[Spyder327]

i only go off what I read.

then you should have a turbonator in your truck :laugh:

 

[Yardie]

i only go off what I read.

 

[VaBchXRunner]

Get em boy:top:

 

[jaxchrisfla]

" There are two types of chassis dynamometers on the market, inertia and loading. An inertia dynamometer (such as DynoJet) does not measure torque, but measures acceleration. A loading dynamometer applies resistance that is measured (using some type of strain gauge.) The most often heard discussion is that what factor can be applied to rear wheel horsepower to reflect crankshaft horsepower. This is where we need to understand how the rear wheel horsepower number was derived. Since the DynoJet seems to be widely used and numbers quoted are those from a DynoJet, we are going to use them as our inertia dynamometer example.

First it is important to have an understanding of how DynoJet gets their horsepower numbers. Power in mechanical terms is the ability to accomplish a specified amount of work in a given amount of time. By definition, one horsepower is equal to applying a 550 pound force through a distance of 1 foot in one second. In real terms, it would take 1 HP to raise a 550 pound weight up 1 foot in 1 second. So to measure horsepower, we need to know force (in pounds) and velocity (in feet per second). Dynojet's inertial dynamometer measures power according to the terms just described. It measures velocity directly by measuring the time it takes to rotate two heavy steel drums one turn. It measures force at the surface of the drum by indirectly measuring it's acceleration. Acceleration is simply the difference in velocity at the surface of the drums from one revolution to the next. The force applied to the drums is calculated from acceleration using Newton's 2nd law, Force = Mass * Acceleration. Since the mass of the drums is know and acceleration has been measured, Power (horsepower) can now be calculated. Torque is then calculated using the horsepower number: Torque = Horsepower * 5252 / RPM.

Once they have these numbers a series of correction factors are applied, some made public, some hidden as proprietary secrets. The public correction factor is the SAE correction factor. This formula assumes a mechanical efficiency of 85%. The formula used is: Where: CF= 1.18 * (29.22/Bdo) * ((Square Root(To+460)/537)) – 0.18. To = Intake air temperature in degrees F, Bdo = Dry ambient absolute barometric pressure. This correction factor is meant to predict output in varying atmospheric conditions and is a +/- 7%. The proprietary correction factor is supposed to reflect the loss of power from the crankshaft to the rear wheels.

A Loading Dynamometer applies resistance to the dyne's roller(s) , typically using either a water brake or a current eddy brake. In either case, the amount of force is measure using a strain gauge. The measured force is torque which is a real, indisputable measurement of the actual output at the wheel. Horsepower than can be calculated: Hp = Trq * 5252 / RPM.

A Dynamometer can only measure actual power at the output location. Actual power produced AND delivered by an engine will be highest if measured at the crankshaft, lower at the transmission output shaft and even lower, but more meaningful, still, at the rear wheels. The power that you use is the power at the rear wheels. Some Dynamometer companies add to measured rear wheel power readings a factor that is based on ESTIMATED rear wheel power losses (under what power conditions? 3.0 ltr.? 5.0 ltr.? Under coasting conditions? with a 185/70/15 radial tire? a 335/35/18 radial tire? New heavy radial tire vs. worn old, light, racing tire? Who knows?) In short, there is NO meaningful "average" tire to get a correct rear tire power transmission loss measurement for all cars - so obviously, unless they actually measure the power lost in the rear tires, under driven load conditions, NO dyno company should BE ADDING incorrect power figures into the measured power. It's simply wrong. The fact that they add varying amounts of power to the actual, "true" amount of power delivered and measured to the surface of the drive roller creates a situation that makes it an onerous task to compare power figures from different brands of dynamometer systems. On simple inertial dynamometers, some (most) companies use an average for the inertial mass value of the engine, transmission, driveshaft, axles and rear wheels. This is saying that a 4 cylinder, 2.0 ltr. Porsche 914 has the same rotating mass and same rear wheels as a 8 cylinder, 5.0 ltr. Porsche 928 S+4. This simply is not so and wrong.

It's expensive to measure frictional losses in the engine and drivetrain, requiring the dyno to be able to drive the vehicle with engine off. Add the cost of a 50+hp electric motor, controlled power supply, etc. It's just not likely that $20,000 dyno will be equipped with that equipment. It is also common for dynamometer companies to add to the power readings by adding transmission and driveshaft losses back into the measured power readings. Some companies make a concerted effort try to measure frictional losses and, optionally, add the power to the measured readings. Other companies - some that would surprise you - say that it's not important and give a blanket, single factor for frictional losses in every engine. Some simply say that there is a meaningful "average" for every car,( 4 stroke/ 4 cylinder/ 4 speed transmission, 4 stroke/ 8 cylinder/ automatic transmission) and apply it to every car and that it is not a significant difference. Blanket estimates of "average" losses and corrections are, quite simply, incorrect. At the upper levels of the industry, (we are talking about $150,000 - $500,000 AC or DC 4 quadrant dynamometers) it is not tolerated - shouldn't be - and needn't be. There is a dyno company that actually has different versions of software that displays their own identical data files as different amounts of power depending on whether you use the DOS version or the Windows version of their software!!

True, rear wheel horsepower is the standard of measuring the power that is actually delivered to the rear wheels. It is honest, true, fair and duplicable. It is the ONLY standard that can be duplicated by the entire industry - regardless of the dyno manufacturer. From my experience and that of many others, when comparing True, rear wheel horsepower to DJHP you must apply a factor. It appears that this is a sliding scale based on horsepower but the best estimate is 1.05 to 1.21 (maybe higher). What this means is that for those of you trying to calculate what your crankshaft horsepower is based on DJHP, and are adding 15%, the most common number I hear, you are actually doubling (at least) the factor. Why? Because DJHP already has a puff number added into their DJHP. Lets say DJHP shows 200 hp and you add 15%, you get 230 hp crankshaft horsepower. In reality DJ has already added in 15 or 20% to their 200 DJHP number. How does this help us.? It does not, and is fact harmful to the many dynamometer test facilities that report only what the dyno actually measured. I can not tell you of the many discussions that we have had as to why the horsepower numbers we recorded lower than that of DJ. For those manufacturers that use DJHP as proof of their claims, can you imagine the shock your customers get when the horsepower number of a vehicle tested on a load bearing dyno do not come close to their claim.

Proper tuning, especially on highly modified engines greatly affect the power difference. Due to the fact that the DJ dyno's sweep so quickly on sweep hp tests, there is no way to properly tune a fuel map. What you get is the acceleration and full throttle maps both triggered during the test, ending up over-rich, affecting the horsepower. The other factor that needs to be taken into account is that DJ dynos assume that every vehicle has the same rotating mass - they don't - and that disregard is another reason why the hp conversion figures are different. The most accurate measurement of rear wheel horsepower is in Steady State Mode (inertia is not a factor in power equation.) The inertial mass changes on each car affects the DJ power, but not the true, rear wheel horsepower. There's another message in the above example, besides the average true, rear wheel horsepower to DJHP conversion factor - It's up to the more experienced reader to figure it out.

Chassis dyne HP, What is it? What to call it? DynoJet = "DJHP". It's not really proper to call "DJHP" "rwhp", as neither the Mustang, DynoJet, Fuchs, Superflow or Land and Sea will necessarily produce the same numbers as a DJ dyno, except by luck - and the whole idea of true, rear wheel horsepower is that EVERY dyno manufacturer HAS the capability to provide those numbers! The Superflow chassis dynes, the Mustang, Land and Sea are all capable of measuring power in steady state mode and producing the same numbers - they all measure torque. Torque x rpm / 5252 = horsepower. We've not diddled with physics! The only factor that is added to the measured reading, in true, rear wheel horsepower, is the additional energy (dyne parasitics) required to spin the dyno(s) roller to whatever speed the roller is turning at - logical, proper and required for any measuring instrument, torque x rpm / 5252 = horsepower + parasitic power = true, rear wheel horsepower.

Chassis dyne HP, What can inflate HP readings on a dyno, but not really make more engine power in the real world? A few things can affect HP when using inertia dynos (not a dyne in Steady State Mode) to measure power (what else would you do??: Changing to light, worn race rear tires will improve power output on an inertia dyno, but, not improve real world top speed. A heavier (brand new street) tire that replaced the above, light, worn tire, will decrease measured power on an inertia dyno, but not decrease real world top speed. Lighter wheels are a good thing! Better acceleration in lower gears, especially 1st and 2nd (accelerating less inertial mass!). Better handling is possible, too! Driving hard on worn, light tires is foolish and is not being recommended.

Problems with Inertia dyno test procedure and fuel injected vehicles: A Sweep Test (hold throttle wide open and sweep from low rpm to high rpm) will often trigger the Acceleration Fuel Map, along with the Main Fuel Map, causing the fuel mixture readings to indicate dyno operator that the motor is overly rich. This would cause the tuner to lean out the main fuel map. Of course, in the real world, upper gears, the acceleration rate of the engine is much slower than what they tested, doesn't trigger the Acceleration Fuel Map, and the engine ends up a lot leaner in reality in top gear. It's not that common of a problem, since most people never drive that fast for that long to cause engine damage. Work around: Tune full throttle fueling in real world usage at dragstrip (to best trap speed) or in Steady State Mode on different dyno.

You can optimize tuning for a DJ dyno and make big numbers - and you can tune the engine to make the best power under load on a load bearing dyno and blow off the big DJ dyno numbers. Can a tuner cheat and make a load bearing dyno read higher? The only way that could happen is in a Sweep Test - Sweep Tests are the least reliable of all tests, period. There is NO question about that. Since the Rotating Mass is a variable in a Sweep Test (NOT a Steady State Test!), the actual inertia factor entered affects the final HP figure - Tell the software that the vehicle has a lot of rotating mass to accelerate, and the HP number increases. (torque, rpm, acceleration rate and mass are the factors) - just like DJ dyno ignoring the difference in mass of all cars - So - true HP, again - Steady State Test - No acceleration, mass makes no difference, anymore. Torque, RPM and dyne parasitics. Period. True. Can you make a Steady State Test read higher? Really hard to do - The software will NOT take data unless speed and load are completely stable - eliminating cheating. As far as atmospheric conditions making a +/- 10% difference? Unless you REALLY mess with the barometric pressure (and you can look at every atmospheric factor on the test report sheet - it's hard coded to display - and not an option), it is simply, absolutely impossible to do without obvious evidence. Are final tuning optimal dyno settings different on an Inertia dyno vs. a load bearing dyno? For many reasons, final tune settings are different - and, since most load bearing dyno's will do both , there is a choice of tests - from a DJ style Sweep Test to Steady State. Having a choice of those types of tests to do and seeing what the results on the track are, most tuners will choose the Steady State Test over a Sweep Test. Without a doubt - the Steady State test Mode is the most consistently superior method of tuning - anybody who has the capability to do it will echo that sentiment - it's only an arguable point with those who can't do it properly. One of the reasons why the load bearing dyno will provide settings that work better in the real world is that combustion chamber temperatures are more in line with the actual operating temperatures that the engine.

Does altitude make any difference at all in horsepower? The engine couldn't give 2 hoots at what altitude it is tested at - it only cares what the air pressure, temperature and humidity is. Sea level at 28.02 inches baro is exactly the same as 4000 ft at 28.02 inches, as far as the engine is concerned. When tested at 5000 ft, we get virtually exactly the same power (corrected to atmospheric conditions, of course) as we do at sea level - It's just about 24%-25% less on the track! I am confused why some dyno operators insist on putting altitude on their charts and swear that it's a factor.

Crankshaft horsepower vs. true rear wheel horsepower. That's a tough one. As each vehicle is different, the best way is to dyno the engine and then dyno the vehicle to see exactly what the loss is. The best estimate I can give you based on experience and research is take crankshaft horsepower, subtract 14.5% ( search SAE ), take that, and subtract around 10% to 15% and you'll get about true horsepower at the rear wheels. The actual formula contains a curve for power loss through gears and there's another curve for power lost in a tire. Remember, too - that unless you dyno your engine you are only likely to get a crankshaft number from the manufacturer and that's probably a "good" one that the marketing department is providing."

 

[ntinhri]

Our research and development dyno is a Dynapack™ dyno. Dynapack™ chassis dynometers measure power generated from the hub of the wheel, and outputs the power generated at the wheels based on a mathematical calculation, like any dyno does.

In the calibration file of every vehicle on a Dynapack™ dyno the following parameters are entered.

Drive Ratio
Car Weight
Diameter of wheel
Gear

These parameters affect the final results which is why it’s very important to make sure these are measured correctly.

The mathematics behind the dyno software generates a mathematical equation per vehicle to estimate the amount of power produced at the wheels. This number its self is in theory arbitrary and is only a number base on certain calibrations and theories.

Can you compare results from one dyno to another dyno ? In short no you can’t

The only comparison which is of any significance is testing a cars performance with modifications A vs modifications B on the same dyno with the same calibration file, within a short period of time.

We choose a Dynapack™ dyno to conduct our research due to them being far accurate and precise than a roller dyno. We can measure very slight differences in power (0.3%) allowing us to have absolute and full confidence in our dyno. Roller dynos in our eyes are open to far to much ambiguously factors such as, the tighter you tie a car into the dyno the more friction between the rubber on the wheels and the rollers on the dyno, this in turn applies more load to the engine making it harder for it to make power. You can not accurately account for this difference each and every time a car goes on the dyno the straps will be a different tension. Other important factors are tire pressure, tire position on the roller, direction the tire is facing and temperate of the tire, all of these uncontrollable factors effect the power. With a Dynapack™ dyno all of these unknown and unaccountable factors are eliminated by the removal of the wheels, which are accurately measured and then accounted for in the final figures.

Can you compare a Dynapack™ dyno to a roller dyno ? Is there a % difference ?

No in short you can’t. You can not say Dyno A is X percent different than dyno B there is no general rule.

Remember a dynos are not an accurate power output device. A dyno is a tuning tool which allows a tuner to apply variable amounts of load on an engine testing its performance in all load and throttle positions. The only conclusive evidence which can be drawn from any dyno is a before and after result. A car started off with this much power, and now has this much.

Due to the nature of a Dynapack™ dyno not having as many environmental variable conditions it is much more accurate to compare different vehicles on the same dyno, due to the fact you don’t have to account for conditions such as strap tension.

The Dynapack™ direct couples to the wheel hubs and applies a precisely controlled hydraulic load. This method of direct coupling plus its built-in strength means the Dynapack™ is always in control of the vehicle.


Flexible data presentation and analysis is available direct from the Dynapack™ in seconds.

Dynapack™ chassis dynamometers are such a radical departure from the stereotypical roller dyno that it really is in a class of its own. Most of the previous assumptions made about chassis dynos (the roller type) simply do not apply to the Dynapack™ series.

Dynapack™ attaches directly to the axle(s), thereby overcoming all the disadvantages of tyre distortion including noise, torque steer, loss of traction, tyre heat and design variations in the tyre.

• Precise engine results - no inertia to mask faults
• Repeatable - accurate back to back runs within 0.3%
• Portability - on and off site
• Stress free - 2 to 30 sec. runs for all data types.
• Minimal noise level - no tyre interface

 

[VaBchXRunner]

can someone break that down, that is wayyyyyyy tooooo long

 

[utixrunner]

can someone break that down, that is wayyyyyyy tooooo long

ya is there a cliff notes of it?

 

[VaBchXRunner]

DING DING DING

 

[Yardie]

 

[ntinhri]

[FONT=Arial,Helvetica,sans-serif]How the Dynapack Works
[/FONT]

[FONT=Arial,Helvetica,sans-serif]A Dynapack is a chassis dyno that uses hydraulic loading to test and measure the output of an engine. A chassis dyno is a tool that measures engine output while the engine is still in the car (vs. an engine dyno, which measures output on a test stand without transmission, etc.).

Chassis dynos use one of two basic means to test engines. One is inertial loading, where a large mass of known inertia is accelerated by the test vehicle. This is a simple, but somewhat limited method for testing. The other method, used by Dynapack, involves a load control mechanism that places an operator controlled load on the engine using electrical (eddy current) or hydraulic (fluid pressure) systems. The advantage of a load control type dyno is the ability to simulate a wider variety of real world situations on the dyno. Additionally, because operating conditions can be fixed, hp changes are far easier to measure.

The final difference between a Dynapack and virtually all other chassis dynos on the market today is that the Dynapack eliminates the tire to "road" interface. By using a special hub adaptor that replaces the wheel and tire, the Dynapack eliminates wheel slip, alignment losses, tire inflation/wear issues and more. However, by eliminating the large mass (and attendant inertia) of the wheel and tire combination, the Dynapack does tend to read higher than comparable "roller" dynos.

How much higher a Dynapack reads is often the source of consternation and debate among enthusiasts wishing to compare numbers across different dyno types. Our first response is, "don't bother". We feel that the primary purpose of a chassis dyno is to measure differences from parts changes, tuning and the like. However, we also understand that bench racing is very common, and trying to ascertain where one stands versus a competitor is a valid pursuit. In light of this, we've undertaken a brief (and simplified) physics calculation to give people some ideas of how a Dynapack measurement will vary vs. the most common inertial dyno, the Dynojet 248C (let's give credit where credit is due, the Dynojet revolutionized the chassis dyno market and brought dyno availability to the masses).

There are two primary differences between the Dynojet and the Dynapack. The first is very clear when you see them. The Dynapack requires removing the drive wheels and tires from the test vehicle. The second is that the load time (the time it takes to accelerate the test vehicle over a specific rpm range) is operator controlled (and fixed if so desired) on the Dynapack. On the Dynojet, load time is controlled by the amount of hp produced, and by the gear ratio chosen by the operator. We will address both of these in our calculations. (all calcs will be done in metric terms and we will convert to more commonly used hp and lbs-ft at the end)

The first concept we need to understand is that of inertia. In particular, the inertia of a rotating mass. For this we will need to know something called "Moment of Inertia" or MoI as we shall call it. MoI uses the term kg-m^2. MoI is basically dependent upon the mass of the object, and how far that mass is distributed from the center of rotation. The higher the mass, or the further it is from the center of rotation, the higher the MoI.

In order to calculate the MoI of a wheel tire combo, we really need to measure the particular wheel and tire. However, we can easily make some reasonable estimates based upon what we do know of the wheel and tire.

Let's start with a couple of typical FWD wheel and tire sizes (since we had a couple lying around the shop to measure). First, a 17"x7" wheel with a 215/45/17 tire. The tire has a mass of 10.86 kg. The wheel has a mass of 8.5 kg.

We will approximate the MoI of the wheel by using a point mass model where the MoI (or I) = mr^2. To approximate our 17" wheel with spokes, we will use a 15" effective diameter as a rough estimate.

Thus, the MoI of the wheel is (8.5kg*(.1905m)^2)) = 0.3085 kg-m^2

We shall use the same equation to calculate the MoI of the tire, using the outside radius (24") less a small correction (1") since most of the mass of the tire is concentrated in the belt and tread surfaces.

Thus, the MoI of the tire is (10.86kg*(.2921m)^2)) = 0.9266 kg-m^2

Making our total MoI for a single wheel/tire = 1.2351 kg-m^2

Now that we know the MoI, we must determine the angular acceleration of the wheel/tire to calculate total torque required to accelerate the mass. On our Dynapack, for the typical street car, we use an acceleration rate of 500 rpm/sec (engine rpm) during ramp runs. With a 4:1 total gearing reduction (not unusual for a 4th gear run), our acceleration rate at the hubs is 125 rpm/sec. This equates to 2.0833 rev/sec^2, or 13.09 rad/sec^2.

When we multiply MoI by the acceleration rate in radians, we end up with a torque in newton-meters (kg-m^2/sec^2) = 1.2351 kg-m^2 * 13.09 rad/sec^2 = 16.168 N-m or 11.93 lbs-ft of torque. This is the torque required to accelerate a wheel with our calculated Moment of Inertia at the rate described. However, since most dynos return a torque calculated by measuring wheel torque and then dividing by gear ratio, the difference in dyno torque as printed on your dyno sheet would be 11.93 lbs-ft/4 = 2.98 lbs-ft. Finally, since this is per wheel, on a two wheel drive car, the total torque loss would be 5.96 lbs-ft.

Thus, the minimum expected difference between a Dynapack and a Dynojet (for this particular wheel/tire combo) would be 5.96 lbs-ft of torque (the Dynapack would read higher). If we were making peak power at 8000 rpm, we would expect the power difference to be approximately 5.96(8000/5252) = 9.08 hp. This is the difference solely attributable to inertia, and assumes that the acceleration rates on both dynos are the same.

These losses do not take into account rolling drag, tire scrub or tire flex (related to inflation pressure, vehicle weight and strap down tension). In testing on Dynojets, we have found that a change in camber of about 2 deg can result in a 5-6 hp change in measured power. However, these are extremely difficult to quantify - but be advised, they do exist on roller dynos, but not on the Dynapack (thus another source of differences).

As power increases for a given combo, the difference will grow due to the change in acceleration rate on the Dynojet (assuming the same gear is used for all tests). As the acceleration rate goes up, the total torque required to accelerate the wheels and tires will go up (remember, the torque calculation is MoI * acceleration - twice the acceleration rate requires twice the torque). But on the Dynapack the acceleration rate is kept the same (or at least should be), so losses remain largely the same. Furthermore, both dynos are subject to inertial losses accelerating the flywheel, transmission, etc. and the faster acceleration rate as hp climbs will show increasing losses on the fixed load Dynojet.

This is why we recommend people use a rough percentage adjustment to estimate flywheel hp on the Dynojet versus a rough fixed adjustment on the Dynapack. In our experience, a manual transmission FWD car will lose 20-25 hp to the hubs on the Dynapack. A RWD car will lose 25-30 hp and an AWD car about 35-40 hp (the FWD case has been verified on an engine dyno). In contrast, losses on the Dynojet will be in the 12-14% range for FWD and 14-16% for RWD (opinions vary).

Let's work through a comparative example for the same car on a Dynapack and Dynojet.

Car A produces 205 hp to the hubs on the Dynapack. This would equate to between 225-230 hp at the flywheel. The same car produces 195 hp to the rollers on a Dynojet. This would equate to 222-226 hp at the flywheel. Furthermore, the difference in power matches up very well with our calculated difference due to inertial losses. And interestingly enough, we have tested just such a car on our Dynapack and a Dynojet back to back with the same results (actually 196 vs. 206 hp).

Let us then assume that we modify Car A to produce 25 hp more at the flywheel (maybe a good head port and set of camshafts). The car would now produce almost 230 hub hp on the Dynapack, but on the Dynojet it would produce 217.5 hp. Same car, but the difference between the two dynos has grown from 10 to 12.5 hp, largely due to inertial effects.

Please keep in mind that these are rough approximations based upon some loose physics and real world experiences. But they should provide a better insight into the difference between loaded and inertial dynos, and hub vs. roller dynos, along with assisting the user in trying to compare results across the different systems.
[/FONT]

 

[ntinhri]

cliff notes taking your wheels off get you more hp on dyna pack.... placement of tires on rollers and strap tention will take away hp...

 

[Spyder327]

those aren't supposed to be the cliff notes right?

 

[VaBchXRunner]

call guiness----longest post ever
damn post whores

 

[Jonathan]

lol this thread is funny, and way too long.

plus, common now steve, we dont need a stickin dyno to figure out our trucks are fast :driver:

 

[ntinhri]

How is a Dynapack different?

The first and most obvious difference is the elimination of the tire to roller interface on a conventional roller dyno. The Dynapack eliminates this variable by using a hub adapter that provides a direct coupling to our Power Absorption Units. There can be no tire slip, no rolling resistance, and no chance of the vehicle coming off of the dyno at high speeds. Notice that we call this a variable. Sometimes it may be a problem area, other times it may not. Tire temperature, pressure, traction, etc, are all variables that can change - not only from run to run, but during the run as well. Throw an unknown variable like this into the equation and your data has now become subject to a potentially high margin of error. It is obviously better if these variables could be eliminated - which is exactly what we have done. There are other associated problems with the roller method as well. Take tie-down straps for example. Most roller dynos use ratcheting tie-down straps to attempt to hold the vehicle in position while being tested. If the straps are cinched down tightly, the tire has become loaded even further, in an unpredictable manner. While this may be good for enhancing traction, it changes the rolling resistance of the tire - skewing the data further. Since these tie-down straps aren’t perfect, the vehicle squirms around on the rollers - dramatically changing the tire drag during the run. If the vehicle is tested in two different sessions, the straps can’t be set exactly the same way twice in a row. Again, the data will be inconsistent. We have heard of cases where the ratcheting tie-down straps were loosened by two clicks and the measured power increased by ten horsepower. What if the straps stretch - either from run to run, or during the run itself? Wouldn’t it be great if all of these problems could disappear? With a Dynapack, they were never there in the first place.

Another major difference is the effect of inertia. Street wheels and tires spinning at high RPM have a large amount of inertia. A large steel drum spinning at the same ground speed has much more inertia. What you end up with is a giant, heavy flywheel attached to your engine. The inertia is such, that just trying to accelerate the mass of the roller is a substantial load for the engine. That is the principle that some roller dynos (or “inertia dynos” as they are also called) operate on. Accelerate a known mass to a measured speed over a given time and it can be calculated to equal a certain amount of power. There is nothing wrong with this theory, but like many theories, its application in the real world can be troublesome. How do you think your measurements will be effected by being subjected to this large heavy flywheel phenomenon? Will small fluctuations be noticeable? In a word, no. The flywheel effect tends to take small rapid variations and smooth them right out - as energy that should be going into the dyno is being wasted trying to accelerate a large lump of steel. This is great if you want your power curve to look like a smooth pretty line, but it doesn’t give you much insight into what is really occurring. What if you eliminated the flywheel effect? While nothing that has a spinning mass has “no” inertia, when compared the total mass of the wheels, tires, rollers, and other associated hardware of a roller dyno, the inertia of a Dynapack is practically zero. This allows us to precisely measure and display tiny rapid pulses and oddities that you may not have seen before. Now you have a window into areas that no roller dyno will allow you to see. Another benefit of having virtually zero inertia is the ability to change the rate of acceleration at will. In many situations, you may want to accelerate the vehicle at a different rate to simulate a specific condition. With a few simple keystrokes, we allow you to make the vehicle accelerate very quickly, slowly, or anywhere in between. Because of our lack of inertia and total control of the engine speed, we give you choices that none of our competitors can even dream of - and as you know, choices are good!

 

[VaBchXRunner]

enough i can't see anymore:motz::motz: