Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Performance measurement e.g. 4/4

If I understand it correctly in simplified terms, it is basically about two figures that ONLY affect the car and NOT the influence of the chassis dynamometer. These are the two values, firstly the power at the crankshaft, and secondly the power at the drive wheel on the tarmac.
On the chassis dynamometer, BOTH values must be calculated retrospectively, using the data from the drag load measurement.

In the case of measurement at the crankshaft, the drag of the drive train is also taken into account.
In the case of wanting the power number at the tyre, only the drag of the roller dynamometer is added back in.
And all those who write that you should not expect more than a "before and after" measurement are of course right when it comes to measuring only the relative increase in performance due to a change in the engine, best at the same day. Then all the differences mentioned above hardly play a role.

On the rolling road they measure power at the wheels as part one of the run where the car accelrates. They then lift off the accelerator and it measures the drag using the DIN norm as the rear tyres slow the rollers.

They take the drag & add it to the power at the wheels to give you crank BHP.

The issue for six sigma fans is the calibration and guage R&R of the dynamometer. Different rolling roads will give different results but results on the same unit are comparible. So the Morganeers +4 and Richard V6s roadster plus Belle all run on the same rolling road give comparible resluts but the absolute numbers on a different rolling road could / would be different.

I was late with my edit/addition on the post before.
Yes, I agree, my point was, that it should also be possible to measure the net drag of the car in difference to the combined drag of car anf rolling road. Then we would see the power at the tarmac.

Following on from John's post it's a shame the dyno we used (Revivals near Duxford) could not pickup on inlet air temp and compensate accordingly. I was running my OBD2 app during the runs and it was very clear that IAT was soaring over ambient during the runs.

Rolling road dyno flywheel figures are still a guess. Here is an explanation you will like. https://www.linkedin.com/pulse/dyno-theory-chassis-dynamometer-road-load-equation-vibin-jacob/

Of course, as you state, if you are using a dyno for the right reasons (tuning)..such things are best ignored as a world comparison with other cars, using different dynos. .

As a matter of interest, I canvassed UK Morgan race preparers many years ago. The consensus was trad Morgans have a higher percentage of difference between flywheel and rear wheels than most cars.

But I am idly (pun!) curious. I am going to ask John Eales. He should know better than most because he uses an inhouse flywheel dyno and his racing customers often use rolling wheel dynos as well. Let's see if I get an answer. He always has been very kind and we have pals in common.

gmg

Ten years ago, we compared the acceleration on an absolutely empty Autobahn between a US 911SC with 180 hp and a Roadster Sports 3.0 series 3 with 223 hp. So that it wasn't too unfair for the Roadster due to the increasing air resistance, the acceleration was from 70 km/h to approx. 130 km/h. In the end, the Porsche was clearly one or two car lengths ahead of the Roadster. Apart from the better gear ratios, I suspect that the 911 had very little drag, neither a cardan shaft nor steerable drive shafts as in the front-wheel drive.
When Lorne says a Morgan has more drag than other brand newer cars, maybe it's due to slippage in the measurement of the light car, or does the differential in a rigid rear axle have more friction than more modern half shafts?

Well they were used to Cain testing race morgans +4 there. They had to recalibrate to handle the 3.7l and it took time to tie Belle down enough. Certainly as Richard suggest having a passenger would have helped.

I've enjoyed following Montegue's tuning journey with Monty, I followed a similar pathway with a K series Caterham some years ago. Initially moving from a base 1.6 - 112BHP car, with all the correct drivetrain equipment. Initially through to 1.8 - 160BHP then onto 1.8 - 210BHP. We used a rolling road 3 times to get the setup right, but for me it was always the subjective "feel" of the car that instilled satisfaction with the end product (or not!).

What was very noticeable was how the cars character changed through each step, the 160BHP engine being horrible, all or nothing throttle due to roller barrel throttle bodies with a bad flat spot in the middle of the rev range. We smoothed it out some on the first rolling road session but the MBU ECU wasn't very programmable.

The final work, was undertaken by Dave Andrews, one of the go to guys for the K Series. This involved a big valve head, new cams, forged internals and an Emerald programmable ECU. This ECU was brilliant and gave 3 switchable maps, very handy as we did a security map that ticks but over won't drive, everyday map at about 180BHP and the full fat trackday map, which I have to admit I rarely used on the road. At this stage we were still running the standard 4:1 exhaust manifold and sports silencer, it ran so much better. But at the suggestion of Dave Andrews, I had a new exhaust made 4:2:1 with a 7 inch can, this further smoothed out the whole package with a small sacrifice of power down to 195BHP, but at a big improvement in torque and smoothness, it made it all so much more drivable.

There were times when I still missed the simplicity of the original setup, but bury the peddle and work the gears and oh boy that induction roar. So for me I would say the performance measurement is always, whatever the rolling road numbers say, going to depend how it makes the owner feel when driving.

I couldn't agree more

Very true. 3rd gear in Belle with Suffolk roads is heaven