| daoust | -- 11-26-2011 @ 4:05 AM |
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I have a 47 with what I believe to be the standard 3.78:1 rear axle ratio. I noticed that the 46s have a 3.54:1 ratio. What sort of performance differences would I experience switching from the 3.78 to the 3.54? David Daoust
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| supereal | -- 11-26-2011 @ 6:20 AM |
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The 3:78 ratio is designed to provide a compromise between power and speed. Ford flatheads reach the best power band at about 2,500 rpm, where horsepower and torque curves meet. That allowed about 50-55 mph on the highway, with enough power to reach that speed in a reasonable time in average terrain. The 3:54 will increase hiway speeds by about ten mph, but sacrifice low end power in hilly country, making second gear driving more necessary. Unless you live in a level area, the swap probably isn't worth the investment. Driving at today's hiway speeds is not always a wise choice in old vehicles from a safety standpoint. Look for numbers on the center web of your rear axle. Divide the larger number by the smaller one to confirm the ratio, if the gears haven't been changed.
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| TomO | -- 11-26-2011 @ 8:23 AM |
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The 100HP engine in your car should give adequate performance in most areas of the country with a 3.54 ratio. I have driven my 40 Merc in IL, WI, IN, MO, MI and parts of Iowa with no problems. I had to drive most of the time in second gear in the hills in western Wisconsin on the tour for the CNM in 2007, but then so did a lot of other guys with their 3.78. I also had brake fade coming down the hills. If you live in one of the areas of the country where you are going up half of the time, stick with the 3.78. Tom
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| daoust | -- 11-27-2011 @ 4:18 AM |
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Thanks guys. I think I'll stick with what I've got. David Daoust
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