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Discussion Topic:
47 Merc 3.78 gear
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ford38v8 |
12-04-2013 @ 8:04 AM
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Senior
Posts: 2758
Joined: Oct 2009
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Len, to expand on my reply at the fordbarn, I'll agree that you'll lope along at a more comfortable RPM with the 3.54, which would be a significant improvement over a ratio of 4.11, but not so much from a 3.78 ratio. If you are able to do the job yourself, you should save some coin, but it would still take you 50 years to recoup in gas savings the investment in the lower ratio. Also, your stop & go in town driving experience will suffer, as well as reducing the life expectancy of your clutch. I changed my ratio from 4.44 to 3.78, but again, that's a much biggerr difference than from 3.78 to 3.54. Your change is not worth the effort and money.
Alan
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len47merc |
12-04-2013 @ 7:51 AM
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Senior
Posts: 1165
Joined: Oct 2013
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Having just brought this '47 79M Merc back to life after a few decades of storage am surprised (probably shouldn't have been) to find driving at current highway speeds of 65-70 mph results in rpms in the 3,250-3,500 range, respectively, driving up cabin noise from the old flathead as well as significantly and adversely affecting fuel consumption. Am targeting 2,000 - 2,250 rpms for 60 mph long-term. Being quite uncomfortable pushing this 66 year old motor (37,725 original miles) at these higher rpms for even short periods of time I am considering a change in the rear pinion set gear ratio from the original/current 3.78 to 3.54 as advised by multiple sources. Doing the math though suggests the improvement to be marginal at best and has me questioning the value of the investment in time and expense. The Columbia OD cost/value is not worth consideration at this point. Am soliciting input from other members regarding experience in this regard and thoughts. Thanks in advance.
This message was edited by len47merc on 12-4-13 @ 7:53 AM
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