Not Ranked
I have had both Tremec ODs. The .68OD was OK in ERA 755 with a VERY mild stroked 428. My current car, ERA 838 has the .81OD with a mild 496. Both cars had 3.54 rears and 295/50/15 tires.
838 wouldn't have been happy with the .68. The engine doesn't want to pull below 1800rpm and that would have made a .68OD only useful on the interstate and worthless on state highways.
The .81 is great for long trips, especially on 2 lane highways. On the interstate it does spin up a bit at 80mph, but most of our trips are on state highways.
.81 with 3.54 rear is a great choice for a Cobra.
John
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