Help!!!!!!!!!!

[JCviggen]

A wheel dyno measures WHEEL bhp & torque and relies on the operator to CORRECTLY enter the powertrain losses

No respectable dyno requires the operator to enter anything but the specs/layout of the car's powertrain. Coastdown loss measurements are pretty standard these days on anything but the most rudimentary rolling roads. The expensive stuff like MAHA gets very accurate numbers calculated from wheel power and coastdown. It's true that flywheel power can't be measured directly, but because there aren't that many variables in powertrain design and the majority of drag losses is from the wheels/tires and therefore measurable...it's not all that bad or inaccurate per se.

Doesn't mean this particular dyno is necessarily accurate, obviously. But flywheel calculated power is often more representative as there are many things which can influence measured wheel power and produce wildly different numbers. Single/double rollers, tire size type and pressure, wheel weight, temperature etc. A coastdown measurement brings those variables into the open and allows for a better approximation of what the actual engine is putting out.

[PetrolDave]

Wooooooow no need to be so patronising Dave was only asking a simple question, looks like I hit a nerve there.

Not intended to be patronising and no nerves hit - your question showed a lack of understanding of the inaccuracy of estimating flywheel bhp by measuring wheel bhp using a wheel dyno which I was helping you fill.

[PetrolDave]

No respectable dyno requires the operator to enter anything but the specs/layout of the car's powertrain. Coastdown loss measurements are pretty standard these days on anything but the most rudimentary rolling roads.

In this case the 3k-8k time being at the slow end just isn't consistent with a 290bhp flywheel figure (something closer to 350bhp would be in keeping with an 8.8s time). So it seems like either the operator didn't enter the specs/layout correctly (it's not uncommon for dyno operators to omit to specify quattro - which as you know has much higher powertrain losses than 2wd so this will lead to an underestimate of flywheel bhp), or didn't correctly carry out the coastdown loss measurement.

The key factor for me is that 8.8s isn't consistent with 290bhp, so the 290bhp figure has to be treated as highly suspect at the very least.

The bottom line is that accurate absolute measurements of power/bhp cannot be made using a wheel dyno, but they most definitely have a place for before-after or car-to-car comparative measurements.

[Special K C5]

Whats the verdict, did you get up to Ecotune?

[Chuds1]

Whats the verdict, did you get up to Ecotune?

Hi Special K C5 well I was booked into Ecotune on Thursday morning there for 9.30. I turned up and sat about for an hour to them be told they had a problem with one of the rollers. Was pretty disappointed. I leave on Monday for my 2 week trip away so I'm going to get booked in when I come back. Fingers crossed.