Mustang Dyno vs Dynojet

Discussion in 'SRT Hellcat Performance' started by koda711, Jul 2, 2015.

  1. koda711

    koda711 SRT Hellcat Supporter Gold Supporting Member

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    There has been a debate between both dynos, the Mustang dyno has been recognized by a lot of industry experts as more accurate between it and the Dynojet. I am not here to say who's right or wrong but if your having your car put on a dyno do some checking on what type of dyno they are using because the numbers are a lot different. Below is a good summary on both dyno's.

    Dynojet
    "A dynamometer is a device that measures force and power. There are lots of different kinds of dynamometers, including the kind that test springs and shocks, but we don't care about them because I don't have any. I have an inertia-type chassis dynamometer. It measures the force and power that the spinning wheels of an automobile[​IMG] produce. It is not a "brake-type" dyno that measures the power that is actively absorbed by a water, oil, or eddy-current brake or by a generator. An inertia-type chassis dyno consists of two great big heavy drums hooked up to a computer. The wheels of an automobile spin the dyno drums, and the computer measures the speed.
    http://www.bristoldyno.com/info/whatis.htm

    Mustang Dyno
    "Now we go to Mustang dyno’s and other loaded dyno’s. Our Mustang MD-1100SE dyno’s rollers weigh 2560lbs. That is the actual mass of the rollers, much like the DynoJet. That’s about where all the similarities end. When we get a car on our dyno, we enter two constants for the dyno’s algorithms. One being the vehicle[​IMG] weight, the other being what’s called “Horsepower At 50mph”. This is a number that represents how much horsepower it takes for the vehicle to push the air to maintain 50mph. This is used as the aerodynamic force. Mustang dyno’s are also equipped with a eddy currant load cell. Think of a magnetic brake from a freight train. This magnetic brake can apply enough resistance to stall a big rig. Off one side of the eddy currant load cell, there is a cantilever with a 5volt reference load sensor (strain gage). As the rollers are spinning this load sensor is measuring the actual torque being applied. So as the rollers spin, the load sensor is measuring the force being applied, sending that information to the dyno computer, taking into account the two constants entered earlier, computing the amount of resistance needed to be applied to the rollers to load the car so that the force of the rollers resistance is as close to the force the car sees on the street. The dyno is then able to calculate the total force being applied to the rollers in torque, and then taking the derivative of that torque curve to arrive at the horsepower curve. Since torque is an actual force of nature, like gravity and electricity, it can be directly measured. Horsepower is an idea that was thought up by man, and cannot be directly measured, only calculated."

    More
    "Dynojet
    The Dynojet chassis dyno is referred to as an inertia-type dynamometer, because large drums provide an inertial load to the drivetrain instead of a friction brake. The working end of the Dynojet includes two 48-inch diameter drums that are mostly below the surface and driven by the vehicle's drive[​IMG] wheels. In the photos of the Dynojet, notice how the rear wheels are centered on the drums and there is one drum per wheel. This will become important later.
    The vehicle is typically run in the transmission gear closest to 1:1 (Forth gear for manuals and Third gear for automatics) to or a variable load that maintains a preset engine[​IMG] rpm or vehicle speed. This feature is ideal for forcing the vehicle to operate at certain loads for tuning. The Dynojet can also measure air/fuel ratio while testing.


    Mustang
    The Mustang chassis dyno uses an Inertia load as well as an eddy current brake load to simulate the "actual" load (combined aerodynamic plus rolling frictional load) that the vehicle would experience when in motion. Notice in the photos how the rear wheels sit between two smaller 10.7-inch diameter rollers. There has been some discussion about the tires getting "pinched" between the rollers and creating more rolling friction, but no substantial evidence of this could be found. However, Mustang has a dyno (MD-1750) with a single 50-inch diameter roller per wheel that alleviates the wheel-pinch concerns. The internals of the Mustang dyno are composed of an eddy current brake to provide a variable load and an inertial disc to provide a fixed load. Mustang claims because its dyno loads the vehicle as it would be on the road, you can perform 0-60 mph, 0-100 mph, and quarter-mile measurements on its chassis dyno. Speed Nation has obtained quarter mile times within 0.1 second of actual runs at the track. We're not sure how the launch dynamics are simulated on the Mustang dyno, which
    includes weight transfer, acceleration, jerk (the derivative of acceleration - how fast the acceleration occurs) and some other variables. The Mustang dyno can also measure the air/fuel ratio while testing.


    Correction Factors
    Correction factors are used by both dynos to account for varying atmospheric conditions such as temperature, pressure, and humidity. The measured horsepower and torque are multiplied by the correction factor to obtain the corrected values. This is similar to the corrected times and speeds provided by some quarter mile tracks. Theoretically, you can dyno on a hot day in the high altitude of Denver and on some other cool day at sea level and produce the same corrected horsepower even though the observed horsepower you are producing at each location is different. Both dynos calculate a correction factor based on a Society of Automotive[​IMG] Engineering document (SAE-J1349). When testing was performed on the Dynojet, the correction factor was 1.10, which means the observed numbers were multiplied by 1.10 (adding 10 percent) to get the corrected values. The correction factor for the day when testing was performed on the Mustang dyno was 0.9595 (removing 4.05 percent). The correction factor when road-testing at
    Keystone Raceway was 0.962, a correction reduction of 3.8 percent."
     
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  2. Hector02

    Hector02 Gold Member

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    image.jpg
    This is my charger hellcat with 618 miles on
    This was on a mustang dyno yesterday
     
  3. koda711

    koda711 SRT Hellcat Supporter Gold Supporting Member

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    Hector02,

    Mustang Dyno's are conservative compared to the Dynojet but more accurate from what I have seen. Did you have TC off?
     
  4. Hector02

    Hector02 Gold Member

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    Yes I did
     
  5. koda711

    koda711 SRT Hellcat Supporter Gold Supporting Member

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    554hp x 12% = 620hp or 554 x 1.10 = 609 hp I have seen both these factors used that is what your actual hp is, Dodge says these cars should pull on a dyno 610-620 rwhp. Wait till about 1500 miles if you want to do it again and I will bet it will be higher you are barely broken in at least that is what I found on mine.
     
  6. Hector02

    Hector02 Gold Member

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    560whp mustang dyno X 1.15= 644 dyno jet X 1.12= 721hp crank
    This is what a use to calculate real horsepower
     

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