It's not so much the engine, but the driving style and I can vouch for this.
3 of us locally are running sirio's evo4 on 7mm restrictor with the same pipes maybe the cars are not that identical but the running weight are close enough.
Now both engines are tuned by myself and are close the same engine temps.
One of us was getting 13 mins, the other was 7:30 and the other 10:40
Lap times showed the person who was squeezing the throttle instead of jabbing at it got better lap times and overall fuel economy, whilst the other guy was pretty much rolling every corner his lap times were very consistent but not on the same pace yet his fuel time was a major plus for him.
The 7:30 was hard on the throttle and very very fast on the track.
I used to run 7:30 on the evo4, but now can easily manage 10+ with smooth driving, one more thing you may want to look at which many over look is the throttle servo response speed.
Most people just center the servo horn adjust the trim and EPA and go race.
Instead of being your average joe, take the time to work on the servo response speed to match your throttle finger speed, to achieve this just put your throttle finger and throttle trigger on top of the engine carb and see how it responds to your input now do it slowly and do it real fast and I garantee you will see a difference.
After you got that sorted, try a couple of runs you will see the car respond better to your input on the track, not to mention a increase on your fuel economy since you dont have the abrupt acceleration out of your engine being out of synch with the actual movement of your finger.