Might be of some help in the case of single point open loop systems but a rolling road isn't much use for setting up sequential systems..
The problem with rolling roads regards setting up sequential LPG systems up is that under bonnet temps can be very different compared to actual driving, and since LPG systems attempt to compensate for temp (but don't always do a good job of it), you can see the implications... I don't have a rolling road, but would in any case rather use the combined 'seat of the pants' and lambda technique than attempt to set flat out engine mixture on a rolling road.
Another point - If a sequential system is running anything like properly then under most circumstances it should be running closed loop - and running closed loop any minor calibration issues are compensated for completely. Since your critique is mpg, you won't be using the 'open loop high engine load' area of the fuel map often enough for any adjustment to this area of the fuel map to make a difference to the mpg that you're getting.
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