rear end ratio's

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Nov 15, 2001 | 05:21 PM

nitrous125

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Joined: Mar 2001

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rear end ratio's

Hello all i am wonder what is a good gear ratio right now i have a 3.00 and man my 390 will the heck out of it above 60 but below it doesnt have much take off. Im thinking more along the lines of a 4.11 with a detroit locker. I wont to street race it and i pull a 12,000lb trailer alot too for my boss. So do you all think 4.11 is a good idea.

Nov 15, 2001 | 05:34 PM

proeliator

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Joined: Sep 2000

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From: Oregon

rear end ratio's

It really depends on what you want to do and what your tire size is. 4.11 was a stock ratio on many of the old fords and will keep your low end strong at the sacrifice of top end speeds. I run 4.11s, but then I have 35" tires. 3.00 gears are way too low for a truck in my opinion. As long as you don't enjoy speeding 4.11s should be fine even with stock stized tires...it will be like a different truck as compared to those 3.00s.

Nov 15, 2001 | 10:11 PM

BigBrownTruck

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rear end ratio's

I currently have a 390 w/ T18 4sp, 31" tires and 3.25 rear end. It is somewhat like you say but I wanted that. Before I was running 3.50 w/ 31" tires. I'd say that 3.50 w/ 29" tires was a typical setup that will allow a good comprimise. If you want to caluculate what your RPM's will be at 60 in high gear, heres the formula:
Engine RPM=20168 X Gearratio/tire diameter(inches) (@60mph w/ 1:1 high gear)

BBT

Nov 16, 2001 | 02:47 AM

TravisT

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rear end ratio's

I had a 2wd `66 F100 with a warmed up 352 and a 4:11 posi rear. with 30-inch tires, 60mph was about all I would do on the highway. RPMs were really up there, something like 2700. Too much for a 352. 3:73s are a good all-around ratio for a 2wd pickup, or stock 4x4.

Nov 16, 2001 | 02:55 AM

TravisT

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rear end ratio's

Nov 16, 2001 | 04:37 AM

f150sleeper

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Joined: Mar 2001

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From: South St. Paul, MN

rear end ratio's

My truck turns 2100 rpms at 60 and 2500 rpms at 70 with a 2.75 rear gears and 29 inch tires. Anyone know how much higher the rpms run on an auto as compared to a manual (i.e. torque converter slippage) at highway speeds?

1979 F150 Custom 2wd C4 302 painted ford blue, bored .040 over, flat top pistons with valve reliefs, Edelbrock Performer cam, carb, and intake, stock heads til next spring, MSD Ready-To-Run distributor, MSD Blaster 2 coil, Edelbrock air cleaner and valve covers, Dynomax headers, dual exhaust with Flowmaster 40 Series mufflers, 38 gallon fuel tank(how i can drive it further than around the block) 9" rear end with 2.75 gears and open diff to change to 3.50s and locker next spring.

"Your only as fast as me until the light turns green"

Nov 16, 2001 | 05:54 AM

jowilker

Fleet Owner

Joined: Jun 1999

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From: Creedmoor, North Carolina

rear end ratio's

William, You are correct, the 411 gear behind a 390 would allow you to pull the empire state building down, but you are gonna buy a hecka of a lot more gas, and those FEs already love gas.

I have a 390, Cruse-O-Matic, and 3.00 gears in one of my 66s. I had to drive it about 15 miles yesterday and just love the way it pulls all through the power band. I was out on a new section of 6 lane hiway and had to kiss that 100 on the speedo. That big boy was still pulling hard with pedal to go. Gets the juices flowing, arg arg arg.

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