I get more than 8% better economy, more like 20% but it comes from more than just increased engine efficency from compression increase. The ratio increase alone is just over 2.5 points more so about 10% less fuel just on that but there is also more airflow, double quench pads. Also the increased TQ from all that means a lot less downshifting around here so if you live and drive on long flat roads you may not see much improvement from that if it don't down shift a lot already. Without tuning the extra airflow and exhaust flow means the ratio is gonna be leaned out significantly when it is not adjusting for the o2 sensor readings. Also since it requires less throttle opening and higher vacuum in the intake the computer advances the timing more so all in all there is a lot more advantage to the swap that strictly having more compression.