Aero

You can calibrate your road dyno for exact speed measurements and hence acceleration measurements with the use of a GPS (global positioning device).
Just make a run of about 10 seconds at a constant speed according to the gps ( accuracy within .1 mph ) and look at the road dyno raw data. reprossess data by changing one drive parameter until the figures on the road dyno match the gps reading for that run. I used the tire aspect ratio as my adjustable variable for calibration. Tire size 205/55/48 gave exact figures. the only other varisble of any consequence is weight of car. JUST WEIGH IT with a full tank and use that as a reference. There is no guesing, the road dyno is as accurate as any system made if the parameters are corectly calibrated.
I'm running a modified Saab 9000 Aero turbo 2.3 4 cylinder. Wheel measurements with no correction(ie raw data calculations) 305 lb/ft at 3300 rpm with 226 hp at 5200 rpm. Peak boost 20psi at 3200 rpm tapering to 15 psi at 5000. This is 275+ hp at the flywheel if you want to start throwing in corrections. Measurements made at 36000 ft altitude and temp of 40 f.

J. Daniel

Two items:
The Roaddyno returns higher numbers in the higher gears. So, apparently, the Roaddyno does not take into account what I will call "geared rotational inertia." Crank, clutch, flywheel, belt driven accessories trans input shaft and gears all have a different effective inertia depending on what gear you're in.
Second, altitude correction in the Roaddyno or any dyno for that matter, applied to a turbo engine, will give erroneously high numbers. A turbo engine that has fixed boost, i.e. it will always reach the same maximum boost (not Audi engines), will loose less power than an NA engine. If boost is 1 bar then absolute boost is 2 bar, at 6000 ft an NA engine will loose 18%, but the 1 bar turbo engine will loose only 9% because it only looses 18% of the atmospheric pressure, but still has the full 1 bar boost. A 2 bar engine would loose only 6%.
The Audi engines, which measure mass airflow and adjust boost up or down as required, should have no altitude correction. Variable turbo efficiency at different pressure ratios and flows will, of course, alter the numbers somewhat.
In summary, the Roaddyno is a nice tool to see the effect of changes, but its absolute numbers are meaningless unless it is calibrated against known values.
By the way, the calibration mentioned above makes zero sense to me. 48 inch wheel?? Typo?

Kevin K2

As J. Daniel said, SAE corrections are for na's not turbos. And like any chassis dyno, wheel hp is measured, and will be lower in 2nd vs 3rd due to flywheel type inertias. But, if testing in 3rd, the drag and frontal area input must be very acurate.

Based on the efficient transverse mount, 1.12 drivetrain correction is about right. This puts eng hp around 250 at test site, mabe 10 more if test was done in 2nd gear.

Aero

Definite typo on the wheel size. The 48 refers to the aspect ratio for the tire in the road dyno program. Even though no such tire exists, that parameter can be adjusted in the Dyno porogram in 1 unit increments so I used the aspect ratio to calibrate the dyno speed to the gps speed. 48 is the one that gave the best match.

Aero

2nd gear testing is great for road dyno purposes, as it only requires a slow start at about 2000rpm and a run to redline. Maybee 5 or six seconds, with speeds 20mph to 65 or 70 you don't have speed to clock some worthwhile data.
From the raw data you can read any speed related or derived data you want. example 30 to 60 mph in 2.82 seconds. This is actual speed data measured at 3500 ft elevation. compare that to the new Vette, Jag, M5 times in the latest road and track which were done at sea level.