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Generation 5 1967-1972 F100, F250, F350

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  #1  
Old 03-26-2015, 04:19 PM
Carmack Carmack is offline
 
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Rear end ratio 1971 F-100

I am currently doing my homework and parts list for my build and I am stuck on choosing the right rear end ratio. My current setup is a 1971 351w swap with a potential Tremec T-5 cobra spec transmission. This truck is going to be a daily driver but will be built to have some get-up anyone have any suggestions
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  #2  
Old 03-26-2015, 06:16 PM
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Fellro Fellro is offline
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Well, you have a little more homework to do... What RPM's do you want it to operate in, as in what cruise speed and engine speed do you want, and what are you willing to trade off on the bottom end. If you want lower cruise rpm, you end up with a numerically lower ratio. That will direct you to what range of ratios will be acceptable. Typically mid 3's give good take off, but also good highway cruise. If you want more snap, and aren't going to be running 70+ down the highway, then you can get to 3.73 or 4.10.
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Old 03-26-2015, 07:01 PM
Carmack Carmack is offline
 
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I was thinking anywhere from 2500-3500 cruising rpm no more than 4500-5000 really getting on it i understand the ratios but i havnt really done drive train work so i dont know which will give me what im looking for but thank you for the help if you have anything to learn me please share
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Old 03-26-2015, 07:05 PM
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Use this converter to help you determine tire size and gear ratios to get where you want. It mainly is just about getting the right engine speeds and such through matching up your tire diameter tot he ratio of the driveshaft and the transmission. It isn't tough, just gotta get the best numerical match up to get the results you desire.

http://www.csgnetwork.com/multirpmcalc.html
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My trucks:
The workhorse, 86 F250 4x4 6.9 nat aspirated, 3.25 exhaust, custom intake, electric fuel pump, otherwise well used stock... not real pretty but just loves to work!

The other heavy hauler, 92 F350 2wd dually crew cab, flatbed/toolboxes, 92 Cummins VE 12V with intercooler, NV4500 manual

The beater: 88 F250 4x4, 5.8 5 speed
The project ... 1978 F150 4wd shortbed 351 auto

ASE certified parts specialist
I do most all of my own work so I know who to complain to..Roger
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Old 03-26-2015, 07:33 PM
Carmack Carmack is offline
 
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Thank you as soon as i can ill see what i can come up with. If you wouldnt mind ill run it through to you and let me know what you think?
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Old 03-26-2015, 09:09 PM
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Definitely worth getting an opinion.
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My trucks:
The workhorse, 86 F250 4x4 6.9 nat aspirated, 3.25 exhaust, custom intake, electric fuel pump, otherwise well used stock... not real pretty but just loves to work!

The other heavy hauler, 92 F350 2wd dually crew cab, flatbed/toolboxes, 92 Cummins VE 12V with intercooler, NV4500 manual

The beater: 88 F250 4x4, 5.8 5 speed
The project ... 1978 F150 4wd shortbed 351 auto

ASE certified parts specialist
I do most all of my own work so I know who to complain to..Roger
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Old 03-27-2015, 07:13 PM
Carmack Carmack is offline
 
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I checked it out and with the tranny specs and using 26" tires, and a 3.50 ratio its giving me just under 2000rpm at 70
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Old 03-27-2015, 08:35 PM
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Even a 4.10 would keep you around 2300 at 70...and the added bonus of faster acceleration out of the hole
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Old 03-27-2015, 09:37 PM
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You don't want your cruise too low or it starts dogging out on hills and you have to pull the gear. 2000 is at the bottom the the common power band, so moving it up to 2300 would be about right. 3.73 or 4.10 would be a good one, and you can use taller tires to bring it back down as well. You will find the most common pulling and fun gears are typically 3.73 or 4.10.
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My trucks:
The workhorse, 86 F250 4x4 6.9 nat aspirated, 3.25 exhaust, custom intake, electric fuel pump, otherwise well used stock... not real pretty but just loves to work!

The other heavy hauler, 92 F350 2wd dually crew cab, flatbed/toolboxes, 92 Cummins VE 12V with intercooler, NV4500 manual

The beater: 88 F250 4x4, 5.8 5 speed
The project ... 1978 F150 4wd shortbed 351 auto

ASE certified parts specialist
I do most all of my own work so I know who to complain to..Roger
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  #10  
Old 03-28-2015, 08:31 AM
Carmack Carmack is offline
 
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Thanks ill definantly keep all of this in mind nowthe 4.10 gear is sounding better playing with the concersion chart
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