My OHC-6 cars are not stock, but my 69 Sprint Bird (301 stroked OHC-6) T-5 with 4.10 gears got 22.5 MPG at 70 mph and 17-18 in the city. My stock engined 66 Sprint Lemans 2004R with 3.90 gets 24 with the A/C off at 70 MPH and 22.5 with the A/C on. and about 15 MPG in the city. I added the overdrives mostly for cruising on the highway and in the case of the automatic Lemans to get rid of the miserable ST300 that along with the OHC-6 engine & stock 3.08 gears made driving the car a miserable experiance. You will never make up the $$$ spent on the conversion with the increased gas milage, But it does make a difference with the steep gears I tend to run.
