I know there is a lot of variability in dyno results. Just searched here but couldn't find any comparisons between Mustang, Dynojet, Eddy Current dynos and any others.
I'd like to know how they relate to each other in their readings.
Like, which is the most conservative vs. most optomistic.
Also, which might be considered most accurate.
GM

 

I dyno'd my car on a Dyno Dynamics dyno. See my post here:

http://forums.corvetteforum.com/show....php?t=1495324

Since I knew the numbers looked high, I did some research on dyno types. Here's a good link:

http://www.msprotege.com/forum/archi...123629978.html

 

Link doesn't work.
GM

 

Dynojet seems to be more optimistic than Mustang, others I don't know.

 

Not sure about the brands, but there are (at least) two types of dynos. And of those two types there may be two types!

There are engine and chassis dynos. An engine dyno just bolts up to the engine and measures it's output. A chassis dyno measures power at the rear wheels, usually by strapping the car down with the driven wheels on a roller.

Most chassis dynos are inertial - the car spins up a heavy roller, and the rate at which its speed increases gives the torque, from which the power can be derived. This type of dyno only can measure acceleration, not steady-state power, but it probably gives a more accurate indication of what the car really does on the road provided that the mass of the roller(s) is similar to the mass of the car. It will, in effect, subtract the inertial load of the drive train, because that's being spun up too. If the mass of the rollers is much different than that of the car, the effect of the drive train mass will be different than it would be with the car on the road, and what gear its run in will make some difference.

Of course you can do the same thing by measuring the accleration of the car, as long as you know it's mass. And that method doesn't have the roller mass variable.

A brake dyno converts the energy into heat, and can measure steady-state power. This could be an electrical generator and a means of wasting the power it produces, like a water-cooled resistor. Of course its quite easy to measure the electrical power. I imagine most engine dynos are brake dynos, but I'm not sure about that. At least the ones used by, say, GM in designing and testing engines would be.

 

I think the variables fed into a Dyno program are resposnisble for many discrepancies. I have seen cars that dyno'd on a Winjet here is Dallas drive across town to another Winjet Dyno and the numbers laid down are significantly different. Dyno's can be manipulated and runs should be used as a guideline for measuring you car against itself not other dyno runs.

 

fixed.

 

Great points, and something everyone should consider when talking dyno #s.