Differential Gearing Question [Archive] - 460 Ford Forum

: Differential Gearing Question

11-01-2006, 05:28 PM
I am upgrading from 28 spline to 31 spline axles and so am considering a gear change since I am changing the pumpkin (9 inch) to a 31 spline.

I currently run 3.70 gears with 26.5" diameter M/T Streets. Since I drive it on the street a lot, I am considering changing to 3.25 gears which would lower my cruise rpm and possible improve gas milage. However, I am not sure how much it would impact 1/4 mile times. The car is about 3550 lbs. horsepower peak is 6200 rpm. If it amount to a couple of tenths its ok, but if more I will probably stay with the 3.70 gears. Please advise your thoughts.


Rest of combo is:

466 with ported DOVE's, exhausts opened to CJ, and 2.19" and 1.76" Manley valves.
Cometic .040" head gaskets
Probe forged pistons with 11cc dish, heads slightly relieved and polished to give about 10.3 compression ratio
Scat H-Beam Rods
Torquer II Intake
950 CFM Proform/Holly
Lunati Solid Lift Cam 559/572 Lift, 237/247 Duration (at .050"), Intake C.L. 106/110 installed 4 deg. retarded.
Matching valve springs with titanium retainers
Howards roller rockers
Direct lube lifters
Ford Distributor recurved by Scott
2 " Primary Crites headers
1962 Fairlane estimated 3550 lbs.
C6 with 2800 stall converter

11-01-2006, 05:39 PM
I can't tell you that but I can give you a formula that helps tell what gear ratio is optimum:

Elapsed Time X MPH = 1335 if the number is more than 1335 add more rear gear. If it is less than 1335, reduce rear gear. This helps find optimum gearing for the 1/4.

MPH= (Tire DiameterxRPM)/(Gear Ratiox336) this finds your mph at a certain rpm/gear ratio.

Might help you in making an educated decision.

11-01-2006, 05:46 PM
Going to the 3.25's probably won't change your trap speed by much, but your short times are gonna suck by comparison.

I used to concern myself with fuel economy..........then I realized that "BBF gas miser" was an oxymoron......kinda like "sanitary landfill" or "reality TV". :lol:

11-01-2006, 05:52 PM
Or Military Intellegence? I hear ya.

Using jpierce55's formula, the optimums would be around 4.00. Maybe I should just go the other way and put in 4.11s and trailer it to the track.


11-01-2006, 05:55 PM
How about "bagpipe music"? :roll:

11-01-2006, 05:58 PM
Or maybe "Super Chevy"? Somebody stop me! :lol:

11-01-2006, 05:59 PM
Sorta sounds similar to running over a cat slowly

11-01-2006, 06:02 PM
This is a typical 460ford.com string. We have gone from rear gears to bagpipes to squashed cats

11-01-2006, 06:12 PM
Where else can you find quality entertainment like this?..........and it's so afFORDable, too!

11-01-2006, 06:36 PM
Yes, it's aFORDable, but just think of all the professional comedians that we are putting out of work. Why they may be "driven" to enroll in the Betty "Ford" clinic.

Yuk yuk. We better stop or Chillie will disown us.

11-01-2006, 06:52 PM
Hey.......Fairlane62.....Do you currently drive one of those? I ask because I have a soft spot for a '62 Fairlane. When I was 17, I used a '62 Fairlane to keep myself in a PECK of trouble. :roll:

Dave D
11-01-2006, 07:09 PM
you guys are great.
Why stop now?

11-01-2006, 07:12 PM
Because, just like Rodney Dangerfield........we don't get no respect.

11-01-2006, 09:27 PM
Either we're like Rodney Daingerfield and we get no respect. Or we're like the Rolling Stones and we get no satisfaction. Either way it's pretty bad since I highjacked my own thread.


Yes I do have a 62 Fairlane. It's a two door post. Basically a early version of a Thunderbolt clone except with a 466.


11-02-2006, 05:10 PM
Mine was a 2-dr post, too. I blew up three 260's (windows in the thinwall cylinders) before I built a 289. This was 1968. My girlfriend's dad ran a machine shop, and he fixed me up with the first set of 289 heads I ever saw with a port job snd 2.02 Chevy valves. Woof, that booger would go....just ask the Michigan State Police. :shock:

11-02-2006, 06:00 PM

I had a 289 in a 67 Cougar with fully ported heads big valves and a Lemans solid cam, 780 Holley etc.

Nothing like the sound of a 289 winding up. Finally blew a clutch which took part of the back of the block with it.

I had a buddy that didn't make it back from Nam in 69 that had a 62 post. I always liked the body style and got this one about 14 years ago.


11-03-2006, 06:06 AM
We digress. :cry: