74 Duster 408 Daily Drivability with 3.73 Gears Vs Stock 3.21 Question.

One of the things that can make a car with deeper gearing miserable to drive is not getting the engine in an rpm range where it is the most efficient.

Crane used to give a cruise rpm range where that specific cam would be the “happiest”. It’s too bad no other cam grinder offered at least a suggestion.

And it goes both ways. In other words, you can run the engine at a cruise rpm that is too high (the gearing is to low) or the cruise rpm is too low (the gearing is too high).

In the former the engine is running with its tongue out and the rpm is higher than it should be so the engine almost hunts for a taller gear. The engine is struggling because the rpm range is higher than enough that the length of the manifold runners and the header primarily tube length is out of tune far enough to cause the engine to struggle.

In the latter the is lumbering along with the rpm too low and it’s almost hunting for a lower gear and the manifold runner length and header primary tube length is out of tune far enough to cause the engine to struggle.

99% of the time we are stuck with manifold runner length and header primary tube lengths. Very few are building custom intake manifolds and headers.

The other factor is cam timing. It is the easiest to change.

To me, there is nothing more miserable to drive than an engine with gearing that is too tall and the cruise rpm is low and the engine is lumbering along. I detest that.

I can live with an engine that is hooked to gearing that is low and the cruise rpm is too high. That is far less miserable to me than the other way.

The other thing that affects what an engine is like under low load, high vacuum driving is the tune up.

Suffice it to say it it at least equal in importance than cam timing and the rest of it.

Probably even more so.