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Originally Posted by stingray72
Snip... Anyways I was considering putting it in the C-10 but is it overkill? I mean I think I could get $800 or so for it (retails for $1300 and was never installed). Is the change worth it? What kind of gas mileage change will I notice with the overdrive?
Once I get my 70 back from body guy I plan on driving it quite a bit
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In a perfect world, you would see 30% better mileage in a .7 to 1 OD tranny like the 700r4 is. However the world isn't perfect.
What is nice about the 700r4 is that with the lock-up converter you won't be generating heat if you pull a lot. The more I pull with my th350 the hotter it runs. 700s lock up in 3rd too which is what you should be pulling in.
So if you are getting 10mpg now with the th350, guesstimate 13mpg with the 700r4. Gas is $3.00 - $3.09 around here BEFORE this BP issue up in Alaska. Fire up a spread sheet and start typing in numbers and making assumptions.
Assume you can get $800 for your tranny.
Assume you'd get 13 with the 700r4 installed verses 10 without (30%).
You can buy 258.9 gallons of gas with $800 at 3.09/gallon.
258.9 * 10mpg = 2588 miles worth of gas with that $800 if you don't sell the 700r4.
That same $800 will get you 3365 miles down the road with a 700r4 installed assuming 30% better fuel mileage.
3365-2588 = 777 miles further with the 700r4 verses the th350 with the above assumptions.
I usually turn it around to figure out savings.
I drive my truck approximately 1000 miles a year.
1000 miles per year at 10 mpg is 100 gallon of gas per year with a th350.
At 3.09/gallon that is $309 for fuel per year.
1000 miles at 13 mpg is 76.9 gallons of gas. At $3.09 that is $237.69.
I would save $71/year. So at $3.09/gallon it would take me 11+ years to save $800 in fuel at today's fuel price.
DON'T FORGET, ADJUSTING FOR INFLATION, gas is still cheaper now than during the fuel crunch when Carter was president.
NOTE: The above does not include other factors like running 30% less rpms at 70 mph which is a very noticable sound difference in the cab of my truck. 30% less rpms all around assuming you don't drive around in town all day will in the long run effect the life of your engine. 30% less r's with a 3.08 rear end may NEGATIVELY effect your gas mileage as some on this list have discovered.
You have to weigh all these things for YOUR truck and YOUR style of driving then make the decision.