High Speed Gears or Overdrive

You might ask high speed gears or overdrive?  Both are a good way for engine relief and less stressful driving on your Model A.  Most A drivers are not interested in driving faster but in dropping engine rpm for less wear and less noise for more enjoyable cruising speeds.  Before going this route, it must be understood if your car can handle the upgrade.  Are your brakes sufficient and will your engine pull the gear change?

It’s not going to help changing gears, if you have a tired engine.  A well-tuned engine with a high compression head is needed to pull the higher ratio.  Without it you will notice no difference in performance.

A 3.78 ratio is standard in most A’s.  Changing to a 3.54 ratio is an 11%increase.  The new 3.27 ratio is a 27% increase.  Most overdrive units are a 27% increase as well.

Some questions I receive are:  Do you have trouble on hills and starting from a dead stop?  I have had a 3.27 since 2001 and have not experienced any problems with hills or even mountains.  If on major hills I do downshift, I am able to go 30 mph in second gear without over revving the engine.  Pulling away from a dead stop is easy because low gear is so low a lot of people don’t even use first gear under normal driving conditions.

Below is a chart to help gauge the difference in ratios and tire size.  Most pickups use 4:11/1 gear ratios, so I include it.  Normal cruising speeds seem to be at 2,000 rpms.  Ford rated the horsepower at 2,600 rpms.

MPH @ 2000 RPM

RATIO                  28” TIRES            29” TIRES            30” TIRES            31” TIRES

4.11/1                   40.28                 41.73                     43.17                    44.60

3.78/1                   43.80                 45.37                     46.93                    48.50

3.54/1                   46.77                 48.45                     50.08                    51.78

3.27/1                  50.64                  52.44                     54.23                    56.06

MPH @ 2500 RPM

RATIO                  28” TIRES            29” TIRES            30” TIRES            31” TIRES

4.11/1                50.41                     52.21                    54.01                   55.81

3.78/1                54.81                     56.77                    58.73                   60.69

3.54/1                58.53                     60.62                    62.71                   64.80

3.27/1                63.36                     65.87                    67.86                   70.15

This article was printed in the March/April 2006 issue of the “A” Quail Call by AJ Pennington.

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