no doubting the SR20DET is a powerful option but you can't compare an RB30ET in a commodore to one in a 240Z..........trust me :
as for mileage,better than the L28 with 2" su's that was in the car previously
2 reasons,
1-changed to 3.36:1 diff ratio as the car is so light that it wasn't loading up the turbo enough to get maximum boost in the first 2 gears
2-the MX7 5 speed has a good overdrive ratio in 5th
of course the economy suffers if you want to feel the boost all the time,but the real advantage to a 3.0l turbo is that you can potter around like a granny off boost(as in daily driver) but when you nail it all the power is there.....kind of like having a daily driver and a drag car all in one (unlike a cammed/carbed/compressed NA that sucks fuel regardless of how you drive it)
the motor runs safely on 91 octane unleaded but i always use premium anyway
the motor is capable of much more horsepower with a more aggressive tune,bigger turbo and bigger injectors but it is plenty fast enough for what i am asking ,dollar per hp it would be hard to beat!
i am looking at another 240z next week,so may end up repowering that in which case the rb30et will stay where it is and i will keep the car until it sells for $15,000 or just hang on to it.
ps the rb30et Z was much faster than the boss 302 one ,pictured in my avatar,which i recently sold....and that was far from slow