I'm not questioning your power, tuning, or weight difference, just your math is off, maybe you're using Imperial Gallons?
55 liters = 14.5 US Gallons, or about 29 mpg.
8 liters/km = 18.8 miles mpg.
I get the 30 mpg with my B13 on the highway, and that's hardly Prius territory. I also get that with my G, despite its 3400 lb hefty footprint. Once you're rolling in that car in 6th gear, mpg shoots about 30. If you're maintaining momentum, the difference due to weight matters very little. Add superior aerodynamics of a V35C with zero lift under-body kit, precise suspension and zero toe alignment, it rolls just fine.
The heft really shows with the starting and stopping, when I have a lot of in-between town driving w/o freeway, I see a lot less, 17-19 mpg. So mentioning you carry a lot less weight than a Z/G, your hwy mpg still isn't going to be that much better, and the math needs work
But I digress
Great swap, love to see detailed writeup, photos, anything because that would be a great B13 setup, the motor is light, buckets of torque, big fun.
