2 different dynos,2 very different numbers.why?

It's not all that easy to jerk the dyno around and make it lie. I've got a balance knob under the console and can move things around 7-8 lb-ft. But why?

However, you can load the engine differently and make big power changes.

As an extreme example. Put an engine on the dyno and load it manually. First no load and 6,000 rpm. If you don't load it, it makes no torque. 0 lb-ft / 5252 X 6000 = 0 HP. Now load it so it makes 200 lb-ft / 5252 X 6000 = 288 HP. If the engine will do it, 500 lb-ft / 5252 X 6000 = 571 HP. All three are accurate readings but vary greatly.

You can even load an engine so hard it cannot pull the load at rpm. It will stall and not accelerate.

There is a difference in power readings by running the dyno at 600 rpm/sec acceleration rate and 300 rpm/sec acceleration rate. 300 rpm holds the engine back and makes it work harder. You get different HP and TQ readings, but neither is a lie.

I took my Demon to a chassis dyno contest at a car show where they were running diesel trucks on the dyno. Talked them into letting me run 'Tetanus' on the dyno. 596 RWHP. That sure wasn't right.

So I asked the operator if he changed the load before my run. And he said he put the load for a car. I said this isn't a regular car, increase the load like you would for a diesel. (Make it push against more resistance and make the engine work harder). The result? 650 RWHP.

You cannot race two different dynos or flow benches. But you can use one to see how changes in design effect the power.