Dyno engine with decreasing rpm

[Circlotron]

Just saw a youtube video where they were dynoing a small engine but running the rpm downward instead of the usual upward. Not sure why except that if the torque increased with decreasing rpm then it would make the loading effect easier to control. Maybe less problems with engine temperature affecting results?

https://www.youtube.com/watch?v=TpdS6090-vU

Edit -> If you don't know where peak hp occurs then of course you have to use rising rpm for the test, but once you have found that point is there any advantage to using falling rpm for subsequent tests?

[user-23911]

We've done the same .......easy with a diesel and waterbrake due to the programming of the governor for RPM limiting.

Full throttle, full RPM, gradually increase the load setting of the waterbrake and revs drop.
The full load running heatsoaks everything so at low loads it's fully heated.
Otherwise at low loads it's cold and heats up through the run.


You probably wouldn't want to do that with an unprogrammed combo because it won't be right.
No problem if already tuned.


Getting a HP readout is just for bragging rights, nothing more.
A dyno is for data collection / measurement.

[user-23911]

It gives a better simulation for a truck starting to climb a hill.

As opposed to a dragstrip.

It's also a really good test for the waterbrake as the lower specced ones can't pull the RPM down below 3500.
A good waterbrake will pull the RPM right down to 800 or less when it's maxed out .
Same applies to any other brake, eddy current or friction brakes.

[DaveMcLain]

If they are using a manual load control on the dyno it can be easier to control the engine by sweeping downward. That's how the original Land and Sea dyno worked. With the Land and Sea you would tell the little computer where to start and where to stop recording data and then it would wait for torque and RPM to climb and then record until the RPM reached the low RPM stop point. It worked fine.

[sr4440]

When I test a diesel, that's how I do it. It's super easy on my SF.


Joe

[andyf]

If you sweep an engine both up and down and the numbers are the same then you can be pretty sure that the dyno is properly calibrated. If the numbers are different then you might have a inertia constant that is wrong or some other finger in the pie.

[sr4440]

Andy

One of the 1st things I do to make sure the "inertia correction factor" is correct, is I run a pull that goes up to a set rpm and then back down. If the lines don't lay over each other I use the "post processes" to adjust until I find the correct number. Also since the weight inside every engine is different, it has to be done on each engine.


Joe

[SupStk]

Really don't know if one is more accurate than the other. One of my dynos is a Stuska Trackmaster. With it up pulls and down pulls can be done. From the manual it states if the inertial factor isn't known, it can be adjusted by doing up and down sweeps and tweaking the factor until HP is the same both ways.

[user-23911]

If you do fixed RPM in steps, then there's no inertia to mess things up.

SAE J1349?

[SupStk]

If you do fixed RPM in steps, then there's no inertia to mess things up. SAE J1349?

And when done you could sell your dyno customer a refreshen job! Bonus Bonus!!!!

[user-23911]

Only if it's a bad engine to start with.
Our engine dyno is built to run all day long at whatever RPM and load you want.
An industrial engine can handle it.

If you're doing emissions testing, you have to.
2 minutes continuous at each step?