just be careful going the other way. i just pulled the 342s and instaled 273s to go with the lt1 going in this month and lost 5 mpg.i made the same trip 6 weeks ago with the 342s and averaged 23.6 mpg and this trip got 18.1 with 273s.from idaho to ca. 750 miles.it was only turning 2050 rpm at 75 mph. the carb just isnt efficient at that speed and load.this is a new 350/roller cam w/vortec heads and 700r4.and all of the computer q jet and related systems intact.
the negative change really cought me off gaurd but the # dont lie.i expected a slight increase.so all you guys changeing gears which ever way you go,keep your motor in its sweet spot.i just thought this might be relavent given all the gear changes here and all sorry if it isnt