Dependent on the specific upgrades chosen. Naturally, if we were to take one’s 6.0L engine, stroke it out to 7.0L and develop a race car package and tune for a customer, there is a very high probability that it will in fact consume more fuel.
However, in the majority of circumstances, we actually see significant increases in fuel economy to go hand in hand with outstanding performance gains. When a vehicle makes increased power, it then requires less effort or input from the driver to propel the vehicle at a certain speed,than it did previously. With a more powerful and efficient engine, we can achieve the same desired results as previously (eg. accelerating a vehicle to 60 kmh) with less effort, hence the increase in economy. To add to this, we are also able to tailor specific fuel economy maps if desired, as well as simply improving on the often sub-standard factory mapping with which the vehicle currently reads.