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Hi,
The issue here is the use of the dyno to measure any effect.
It doesn't matter whether it's a Chassis or Inertial Dyno, the effects you're trying to measure are too close to the degree of error to really mean anything.
People wanna sluff these off, but there are so many ways to skew the testing, both consciously and inadvertently. These Dynos are for Tuning, not determining absolute values.
The error possible is just too great, and from little things such as electrical load, gear selection, corrections (either manually or software), etc.
Also, Drivetrain losses are often waay too under/over estimated. All testing s/b be recorded only in 4th gear as this is as close to 1:1 as possible and best measures only the flywheel output. The Frictional losses in the Tranny will only account for a 0.5%-1.0% parasitic loss - not the 18%-22% often just pulled out of the air. Most drivetrain loss occurs in the Tires and varies widely from Tire-to-Tire, so much so that no meaningful generalization can be made.
Each error, such as Temperature or Barometric Pressure, or insufficient cooling, etc. may only introduce errors of 1% or 2%, but these errors compound themselves and soon you have error of 10-15% when your measured gain is 8-10%, meaning that you cannot be sure of any gain at all.
You can try to eliminate errors, such as doing Baseline Runs when the engine is HOT (most don't do this), or have an accurate weather model, again, most don't or plug in regional data which can be very different than at the Dyno itself.
The only Dyno which is accurate for the engine is a Bench Dyno. It measures the flywheel specifically. Chassis or inertial Dynos are only useful in monitoring changes while tuning, and even then are subject to great error if the operator dosen't know what they're doing...
Happy Motoring!... Jim'99
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