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Author
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Topic: rear gear change
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streetstang67
Gearhead Posts: 397
From: SC, USA
Registered: Nov 2002
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posted 02-23-2003 01:02 AM
   
I'm planning on changing out my 2.79 rear gears for 3.55s. How much faster will I be? in the quarter mile? Where will I gain speed? Where will I lose it? Lots of questions  Thanks
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rockafellz
Gearhead Posts: 1443
From: San Lorenzo, CA, USA
Registered: Aug 2001
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posted 02-23-2003 06:22 AM
You'll lose some top speed but gain a ton of low end torque!! ------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress 1966 Ford Mustang Coupe
Dad's - Original Unrestored
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streetstang67
Gearhead Posts: 397
From: SC, USA
Registered: Nov 2002
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posted 02-23-2003 11:02 AM
Since I gain low end and lose top end, would the quarter mile times be much different...do they kind of "even each other out"? About where would I gain: 0-40, 20-60, 40-80....or something else? Thanks again
Would I gain gas mileage in city driving and lose it in highway driving?
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Rory McNeil
Gearhead Posts: 1611
From: Surrey, B.C. Canada
Registered: Nov 2000
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posted 02-23-2003 12:27 PM
Your results will vary greatly, depending on your combination, but should be noticable even on a pure stock vehicle. Years ago, I replaced the 2.47!  7.5" rear end in my bone stock 302 2v, auto 78 Fairmont, with a 8.8 with 3.55 Traction Lock, & knocked a full 1/2 second from my ET slips. With 24" tall tires, the cruising RPM on the freeway went up quite a bit, almost 3000 RPM @60 mph, but not objectionable unless you do lots of freeway driving.Also, as I continued with more modifications, the gears helped them out. After switching to a T5 5speed about 7 years ago, the OD put the freeway revs back down around 2200 rpm, so I may go a bit steeper in the future. Gears are one of the best "bang for the buck" deals going, & a neccesity if you hope to get the most out of your combination.------------------
78 Fairmont 428 4 speed 10.20@130mph
80 Fairmont 302 5 speed 12.8@105mph
85 Mustang NHRA Stocker under construction, 302 5 speed
59 Meteor (Canadian Ford) 2 dr sedan 332, auto
74 F350 ramp truck 390 4spd
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Fastymz
Moderator Posts: 20638
From: Reno Nv USA M&M#1240
Registered: Apr 2001
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posted 02-23-2003 02:24 PM
I'd say you'd pick up about .2 .5 in 1/4.
And a lot more fun around town,your feel the differnece. 
I went from 2.79 to 3.40 gears I too use 24" tires.I can notice a big change around town.I cruise at about 3300 at 65 mph.That does not seem bad to me.------------------
SCOOP
oddly obsessed with big scoops on little Mustangs 2.26 60'S
14.9 @ 90.86MPH 65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede. https://mustangsandmore.com/ubb/Fastymz.html
[This message has been edited by Fastymz (edited 02-23-2003).]
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