VAGCOM Block 120 vs Rolling Road (copy of original thread in Motorway)

[DaveH]

After my first ever RR session I thought it may be interesting (loser, yes I know) to compare what was recorded on the RR against what I recorded using vagcom. I must say I'm pretty impressed, i guess vagcom is a bit more variable owing to instanteous senor readings but overall it looks pretty accurate to me:

[EddyH]

Nice work!

Also gives a good indication of the accuracy of the RR at JBS.

[DaveH]

Originally Posted by EddyH

Nice work!

Also gives a good indication of the accuracy of the RR at JBS.

Yeah, I thought that aswell, do we now have an independent method to substantiate peoples claims, I think so! I also had a quick look at wheel/flywheel losses, the '(whp x 1.1) + 10' formula was near enough spot on for me.

[GaryM]

I believe that block 120 actually measures power at the flywheel and not at the wheels - Just seen many posts on SCN backing this up.

I personally see around 215hp with block 120's.

Also the 4bar FPR seems to create false readings meaning the best way to get a power reading with vagcom is from block 005 using coastdown (butt-dyno), I think its block 005.

http://forums.vwvortex.com/zerothread?id=521365&page=1

Taken from an old post on Vortex:

"VAG-COM numbers are net flywheel torque consisting of the force generated in the combustion process minus engine frictional losses, gas-exchange losses and torque required to drive ancillaries. Some here may not realize it but the torque values are not directly measured but are derived based on engine parameter inputs and known outputs. Engine speed, air mass, inlet temperature, barometric pressure, air pressure before and after the throttle, coolant temperature and run time are measured. Cylinder charge dilution, inertial effects on charge air and fuel, engine friction including pumping losses and ancillary drain are modeled based on test stand data. The data includes values for exhaust backpressure. Fuel delivery, throttle position and ignition timing are commanded. All of this is used to estimate the net torque generated by each cylinder firing. The model uses manifold pressure and engine speed in part to estimate pumping losses; engine speed, coolant temperature and run time to estimate engine drag. The cylinder charge air flow estimate includes adjustments for delays based on the pressure before and after the throttle along with throttle angular velocity and current throttle position. This also goes into estimating fuel delay. Intake storage and release requires additional estimates of intake port and valve head temperatures (derived from intake temp, coolant temp and run time) as well as the change in manifold pressure. Charge efficiency adjustments are made based on backpressure which itself is adjusted based on barometric pressure along with manifold pressure, engine speed and valve timing. Combustion efficiency is adjusted based on air temp, coolant temp, air/fuel ratio, charge dilution and ignition timing. The controller is a torque based management system so every effort is made to accurately derive its value.
Chassis dynos tend to show lower values than VAG-COM, or for that matter, actual road values for a number of reasons.
1) Driveline losses including tires (tire losses are greater on a roller than on a flat road).
2) Static loading and inertial coupling of the dyno with the car.
3) Air flow over radiator and intercoolers. Too low a flow and the drop will be much more than just the density change of air due to temperature. Ignition timing, fuel delivery and charge pressure all interact detrimentally with increasing temperature.

Test stand data tends to show higher numbers. When I did test stand dyno runs 25 years ago, engine coolant was supplied by city water and circulated by an external pump, draft air flow by an external fan and a metal hose connected the exhaust manifolds to the intake of an exhaust blower for evacuation out of the dyno room. I don't know to what degree this "cheating" is done with today's numbers. In prior years they even motored the engine and took those numbers to add to the output numbers."

[DaveH]

Something is a bit off then, I've lost 30hp!! I'll give 105 ago to see what I can see.