Checking your engine performance on a chassis dyno?

[tnewland]

Jerry
You sound like you know a lot about dynos, do you operate one? If the operator of this particular dyno stated that the max MPH of this dyno had been reached at 150 MPH and the dyno sheets have a large red "MAX SPEED !!!" printed on the front of it what leads you to believe that the max MPH had NOT been reached? Also as an operator are you NOT supposed to monitor basic functions (oil pres, engine temp, etc) of the engine during the test to identify any potential problems during the test? Wouldn't potential problems be displayed on the graph the operator is watching as some sort of inconsistency in the line of the graph? As the operator when is the test finished, after the max horse power has been reached and just as the graph starts to taper downward or are you supposed to continue on until the dyno shuts down irrelevant of what both the customer and the computer monitor are indicating? Is the dyno NOT supposed to be used as a diagnostic tool and a controlled enviroment to safely conduct controlled tests? It sounds lie from what you are telling me that I might as well had gone out on a public street and just mashed the pedal to the floor until I hit whatever speed the engine or car finally stopped at? I hope that you are NOT an operator of a dyno as you appear to be the same type of "operator" that STL Mark is warning about! What is the benefit of using a dyno if for no other reason than a diagnostic tool in a controlled safe enviroment?

[STL Mark]

If the engine was stumbling around 4000 it would have been as clear as a bell on the chart during the pull and there would be no need to run it through a full pull - or beyond. A skilled tech can listen to the engine, watch the gauges, and keep an eye on the computer screen all at the same time during a session to make sure that he doesn't blow your engine.

A skilled tech would have listened to your initial complaint, done a couple of test pulls (after checking timing and dizzy) to 4000 RPM or so (maybe), and if they looked good - he may have done a full pull. But he should never do a full pull unless the motor was making good numbers.

If your engine had any sign of erratic or otherwise unstable behavior at any time during a pull - he should have immediately stopped. And going beyond your instructions of 6500 RPM limit is simply insane.

[STL Mark]

Here is an example of a problem spotted on the dyno.
My friends car was "running rough" around 4000 RPM.
He told our dyno guy about it.
He did an initial pull - see the erratic set of HP/TQ lines.
They are broken at about 4300 RPM because the operator stopped the pull.

He then made some corrections to the car (sorry I don't remember what) and did another pull. That second pull where the lines meet about 5000 RPM corrected somewhat but his A/F ratio was off so he discontinued that pull as well.

The engine was never in danger during the session because the operator was paying attention and doing his job.