This seems to be backwards. According to the EPA, a V6 auto is getting slightly higher MPG compared to the 4cyl auto. I had a 93 V6 Camry and the highest I got with that car was 28mpg. But my mother had a 96 Camry 4cyl and i got 34mpg no problem. Both were driven the same way and using the same hypermiling tricks. Full tank,tires, etcs. Is this just another goverment goof up or am I missing something?
"But Doc, we dont' have enough road to get it up to 88 miles per hour"
If you bring a 2007 camry into the mix when doing the comparison, you can see the "old, 1985 EPA numbers". This is useful because now you can see with more precision the fuel economy numbers these cars get and you can see now that the '96 V6 does 2mpg better on the hwy 1mpg worse in the city compared to the '96 I4. The '93 camrys and corollas do worse on the fuel economy tests than their '96+ bretheren, for whatever reason.. In fact, the pre OBD-II Corollas and Camrys have worse fuel economy but more power than their OBD-II counterparts.
How well the car is tuned up and condition it is in can be a factor in fuel economy. As for why a V6 does better on the highway but worse in the city, transmission gearing helps it on the highway but the displacement hurts it in the city. V6 engine could also be of a newer generation compared to the I4 being used.
edit: yup, if you look on wikipedia, the 1MZ engine (V6) first started production in 1994 and is introduced for the 1994 model year while the S engine (I4) was first introduced in 1982 and the 5S-FE used in the Camry is just a later revision... The later camrys get better fuel economy with the I4 compared to the V6 versions, as expected.. Technology trumps displacement! Surprise surprise!