Looking for some help. Again!
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Elder User
Joined: Mar 2006
Posts: 656
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From: Westford,Ma
Looking for some help. Again!
I am getting ready to buy a rear ned for my truck. I have found a place that has explorer rear end with every possible gear ratio. What I need to know is which one will work best with my c-6. I was told it came out of a 73 F250 with a 390 but beyond that I know nothing. I don't want to buy a rear end and change gears if I can get the right one to start. I don't want to put the truck together and find out I top out at 65 miles an hour!
Last edited by daves54; Apr 9, 2010 at 11:00 AM. Reason: add more info
Laughing Gas
Joined: Jan 2008
Posts: 758
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From: Alabama
Depends on your tire size too. Go to this site and it will let you input different numbers to see what your RPM's will be at a given speed. I found a better calculator but its in my favorites at home and I am at work right now.
Engine RPM Calculator
Engine RPM Calculator
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
The 390 has a lot of low end grunt and not a high reving engine so the ratio should be something around 3:00 or even in the upper 2's for best gas mileage. That's what I'd want..
Post Fiend
Joined: May 2008
Posts: 7,641
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From: Poway, Ca.
The tire size wil make a tremendous amount of difference in driveability. I was driving a little too high of an rpm and almost bought a 20% overdrive for my truck (390/C6/2.80rear). I put 235/75R15s on it which were about 3 inches taller in diameter and it gave me almost 10 additional MPH at 2500rpm.
Here is another RPM calculator that I use, and a thread about rear ends that we have had in the past.
Long story short, if you want freeway speeds at 2500 rpm with a DD C6, on 15 inch rims you will need something ratioed not higher than 3.0-2.8 (with 235 series tires), and with 16 inch rims something 3.5-3.25.
Gear Ratio Calculator
https://www.ford-trucks.com/forums/7...alculator.html
Here is another RPM calculator that I use, and a thread about rear ends that we have had in the past.
Long story short, if you want freeway speeds at 2500 rpm with a DD C6, on 15 inch rims you will need something ratioed not higher than 3.0-2.8 (with 235 series tires), and with 16 inch rims something 3.5-3.25.
Gear Ratio Calculator
https://www.ford-trucks.com/forums/7...alculator.html
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jhaas63
1948 - 1956 F1, F100 & Larger F-Series Trucks
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