Re: Explaination of loss and dyno differences..... (archive)

Mustang MD250 vs. Dynojet 248C

Dynojet 248C is actually an accelerometer whereby it uses a 3000-3200 pound drum that is used to create an inertia load on the vehicle being tested. The vehicle's horsepower (HP) and torque try to overcome the weight/inertia of the drum to accelerate it. As a result the software and electronics try to measure the horsepower and torque that the vehicle is developing to overcome the drum's weight and inertia. The resulting horsepower and torque will be higher than a true loading dyno because once the drum starts rolling not as much power is needed to keep it going. Example -- When pushing a car on a flat road, once the car starts moving not as much power (effort) is needed to keep it going. The software does not ask for vehicle weight or anything like horsepower needed to maintain 50 MPH (a number that is actually put out by E.P.A. and N.H.T.S.A.).
The Mustang MD250 dyno is a true loading dyno, because it uses an inertia weight as well as an eddy current motor that is attached to the rollers. This eddy current motor creates a drag on the shaft by way of electricity that causes a magnetic field to try and overcome the torque going through the roller shafts. This current is controlled by software that is always trying to simulate load as if the car is driving in real world conditions. The real benefit from the loading dyno is the ability to maintain a load that allows a tuner to properly go through a fuel map or ignition map and tune the chip for optimum horsepower and torque. It has the ability to also simulate the IM240 emissions test as required in some states. It can check 1/4 mile times as well as times for 0-60 MPH and 0-100 MPH. It can also be used for road testing and simulation for drivability problems. As a result of the loading capability, the dyno numbers from a mustang dyno will come out lower than the inertia (dynojet) dyno.
Hope this explains things, it did for me.

Is that a quote from a Mustang webpage? I couldn't find it at their site.

>The resulting horsepower and torque will be
>higher than a true loading dyno because once the
>drum starts rolling not as much power is needed
>to keep it going.

I don't think that is a good explaination. The dynojet measures the acceleration of the drum and calculates engine torque (which is proportional to the drum's acceleration). If the drum were to stop accelerating, that just means that the torque being applied is zero. Once the drum starts rolling NO torque is needed to keep it going - remember Newton's First Law?

So their explaination is pretty much hogwash. What they should be saying is that engines create different amounts of horsepower at a given rpm depending on how fast they are accelerating and on the recent history of the engine's speed. i.e. engine performance is more complex than just one curve. They should also be saying that both dynos have inherent errors that the errors are not the same between the Mustang and Dynojet.

The Mustang dyno looks to me to be much better than dynojet for serious tuning - like if you're a race engineer with developement bucks to burn.

Follow Ups:

Its from the active auto site.... Mpower007 19:01 5/07/2001 (1)
- Re: Its from the active auto site.... JS 19:10 5/07/2001 (0)

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