Endless debate this one!
And there is a lot of missunderstanding of dynos and how they operate.

The biggest difference between a tarmac and steel "road" is the way the load is controlled.

On Tarmac, the load is controlled by the gear seleceted, the weight of the vehicle and the incline, with varying wind resistance added by speed.

On a dyno, the load is controlled by the retarders (Assuming its a proper load capable dyno and not a crappy inertia dyno.)

Now the load on a dyno is variable by the operator, in fact we can stop dead (stall) about 600BHP per axle if we can keep traction but the key to remember is its usually a fixed figure for a POWER RUN. IE: Dyno Dynamics Shoot 44's flywheel power run has a load ramp rate setting fixed at 100 that we cant change.
What that means is the dyno will "allow" the wheel to accelerate at a controlled rate of 10.0 KPH, per second and vary its load accordingly to achieve that acceleration rate.

So, "if" the dyno run is set to start at 20 KPH and end at 100 KPH, the run will take 8 seconds at 10Kph/ps. So... "if" your vehicle takes 8 seconds to run from 20 KPH to 100 KPH on the tarmac in the same gear, then that run is of a pretty identical load. You are at wide open throttle for exactly the same length of time.

If the load selected is too small, especially on a turbocharged engine, we can have boost spool and peak issue, where the engine runs more boost on the road than it did the dyno and maskes it sooner too. The key is to select a load that mimics the conditions that power level will achieve on the road.
Remember, a 250bhp car will take a LOT longer to do that run than a 1000bhp car.

But its absolutely fine to exceeed the "real" vehicles time and load. If we tell the dyno we want a ramp rate of only 5KPH per second, then thats like the above vehicle accelerating up a hill... its target speed will take twice as long, so lots more load is applied to the engine, the turbo has longer to spool and much more heat is generated.
Its a real test, as on the road we do of course have hills, and pull trailers, and carry more weight.


For running in:
When running a new engine in, we use the Dyno Dynamics excellent scripts system.
I have written a script that varies load with time. So the operator just drives the vehicle and follows instructions on screen. It raises load, allowed rpm, drops load, asks the operator to change gear etc. This is to ensure the operator cant sit at 70mph with a fixed engine speed. We then have some race track simulations that simulate race tracks, indicating gear shigts and what throttle to use, adjusting load for hills etc. It all works very well.


The Future:
Dyno Dynamics have now gone a step further.
So far there is only us with this feature as we are Europes Beta Tester for the platform, but we now have "Road Mode" and have had it about 12 months in various iterations.
We now always input the vehicles weight, and if necessary add a trailor weight etc, or a caravan. The dyno works out the rolling resiatance for any given incline and it simulates the tarmac load for that weight vehicle, increasing the load for wind resistance with road speed etc. We just have a dial to vary the size of the hill. It works a treat.


Summary:
As you guys WELL know, we have spent many many years live mapping on the road and runways and love it...we earnt the money to build our dyno cell from live mapping on the road and have nothing bad to say about it, bar that its very very hard to access all map areas on the road when big speed and corners are also involved. Professionals can do it, and can do it well. Indeed folk like Sheady have to hook up a trailor just to carry their balls along for the journey... but i dont miss it one bit as mine seem to be shrinking with age.

A final test drive on the road after dyno mapping is fine for me nowadays... but then i built cell to replicate the road as best I could afford.
Some dyno cells out there are nowhere near as good as mapping on the road. Bear that in mind... even a good dyno is only as good as its cell abnd its cooling systems. Any cell where you can smell, or even measure hydrocarbons is out for the final calibrations guys...You can build the map on them no bother, but flat out, engines need clean air and LOTS of it.

A video to visualise the loaded run.
Watch the speed on the dyno run and you will see how the dyno is controlling the engines acceleration.
Also note how repeatable the runs on a good dyno are. Thats about the cooling as a rule.



My build blog if your bored:
http://www.motorsport-developments.c...Blackpool.html