Gear swaping, anyone good at math? please help - Ford Powerstroke Diesel Forum
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post #1 of 4 Old 01-12-2010, 08:26 AM Thread Starter
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Gear swaping, anyone good at math? please help

OK, so i got a 95 f-250 stroker, its got the TTB Dana 50 front and 10.25 rear with 3:55's. I plan on swaping in a straight axle D60 front and a D70 rear and also plan to go to 3:73's. Can anyone tell me what kind of rpm difference there would be? my father has an identical truck with 4:10's and the ratio is too "low" for my liking. Living here in Mid Missouri with the hills around here, my truck gets too hot tryin to pull a trailer anywhere, but the catch is i dont pull one often enough to need 4:10's. My question is, will there be a big enough rpm difference to make the ratio swap worth while? I will be swapping the 60 and 70 in regardless and i plan on setting up the axles before installing them so my trucks not down. Thanks for any comments and inputs guys.

1995 f-250 rclb
7.3~317k miles & countin
3" Downpipe
Superduty 10.5" 3 pinion Trac-Lok rear
Dana 60 s.a.s

1997 ccsb , 353,500 miles
5" lift on 315x75x16 cooper at3's.
Clear headlights, tinted tails, rear buckets,
Dana 60 swap, zf5 swap.
rosewood 180/100's, t500 hpop, php hydra, e fuel.
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post #2 of 4 Old 01-12-2010, 08:46 AM
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The difference between 3.55 and 3.73 (it's decimal points, not colons, BTW [or you could say 3.55:1]) is about five percent. So, presuming a ZF5 of that vintage and OEM 235/85R16s, you're doing about 2000 RPM at 70 MPH with your 3.55s, and will be doing 2100 and change with 3.73s. Your dad's truck, on the other hand, revs about 15 percent faster at any given speed/gear, so at 70, he must be doing about 2300 RPM. So the 3.73 is "closer" to the 3.55 than it is to the 4.10.

It's probably worthwhile regardless of the gear ratio, just to have the 60 axle.
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post #3 of 4 Old 01-12-2010, 09:19 AM
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Try one of the online calculators, like this one.

Click here.

99 F350 CCLB 67k miles.

Sold: 01 Dodge cummins ECLB a few more mods to 353hp

Sold: 97 F250 SCLB, 5 speed 2wd. minor mods to 327hp

See a pattern? next I will have to find one of those 6 door jobbers...
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post #4 of 4 Old 01-12-2010, 09:57 AM
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unrelated but be sure and hit the missouri section of the site. were planning a meet last i heard. good luck with your gearing!


Late 99 (2/99) Black F250, CC LB 4x4 Lariat 214k. All Stock for the moment...

1995 PSD, ext cab, one wheel wonder , 297k miles, 30k on wvo. totaled 5/8/11 RIP This truck is for sale as a parts truck (Jason is about to receive forged rods, and drop kick his PMR's)
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