I have ran a lot of different combinations but for an all around Car with a decent cam I found that 3.25 to 3.5 was about right. Anything smaller than a 3.00 ate clutches and was not happy around town. If you have the close ratio this is especially true. I also lost gas mileage in town. 3.73 and above do not give a good cruise. I do like my 3.89s but I do not do a lot of highway driving.
If you do a lot of highspeed cruising go with the 3.25s. More in town but a fair amount of highway the 3.50s.
2.73s gave me 18 mpg on the highway at 65 mph cruise with a best of 25. 3.00s dropped it to about 17. 3.50's gave me 15 this was with a 390, 4spd crower 276Hdp the scode intake and a Holley 03310-2. It was responsive around town and gave about 12 in town.
Going to the 294H cam, edelbrock rpm, Holley 650 dp and 3.89 I figure I am at about 9mpg.
1968 Ranchero 390. 060 over,10.5:1, Comp 292H Cam, Performer RPM intake, Hooker headers, 4spd. 3.89 dif. ProForm 750 DP, Mallory Unilite distributor, Holley Annihilator cd ignition system, centerforce df clutch.
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