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CLICK ON MY AVATAR
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321 Posts
Discussion Starter #1
Hi everyone,
In the near future I will be swapping out the old original 3.08 gears and putting in 3.55 with an eaton posi.I wondering what to expect.This is street only.Will it cruise at 70-75 on the highway?What rpm are we talking.With theres gears will the be alot more get up an go off the line(stoplight)? Is this a job I can do myself or should I leave it to the professionals?I have no experience with rearends at all(no jokes)Thanks BM

Ps I know this is the wrong forum but I'm not getting any bites over there
 

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CLICK ON MY AVATAR
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321 Posts
Discussion Starter #3
25"tires,rear is hooked up to a 350 turbo tranny
 

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Premium Member
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3,519 Posts
well, do the math.

3.08/3.55=


That's a quantifiable way to determine your "kick in the paints" increase.

It will be pretty noticeable.

K
 

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Premium Member
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2,370 Posts
3.55's are still very cruisable gears. I can still do 70 with my 4.11's and 28' tires. I am turning 3300 or so but its doable lol. Just figure you'll be between my RPM at 70 (with 4.11's) and your old RPM at 70 (with the 3.08's).

Your going to really like the new feel.

I would either have the swap done (unless your swapping the whole rear end) or at least have someone handy who has done it before.
 

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52 Posts
Compare Custom Gear Ratios
Gear Ratio #1: 3.08
Gear Ratio #2: 3.55
Tire Diameter: 25
Miles Per Hour: 75
RPM Gear Ratio #1: 3104
RPM Gear Ratio #2: 3578


Approximate Axle Torque
Driveshaft Torque: 250 ft/lbs
Current Gear Ratio: 3.08
New Gear Ratio: 3.55
Torque /w Current Gears: 770 ft/lbs
Torque /w New Gears: 887 ft/lbs

I just went with the driveshaft torque number that is default in the software to show the approximate difference. You can gohere to check it out yourself.
 

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103 Posts
you should have a noticeable difference off the line but rpms on the interstate may be up. im about to undo a previous owners swap of a 308 back to a 373 to get more guts off the line.
 

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Hauling A55 BURNING GASS!!!
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235 Posts
yeah 3.73's are bad if you got to do interstate crusing at 65mph for 4 hours. if i knew how to change gears i would because i have a trip coming up and im just going to tow it because i cant afford gas like that. when towing it should i take off the drive shaft? im leaving the back tires on the ground for the tow.
 

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Brian Morency said:
yeah 3.73's are bad if you got to do interstate crusing at 65mph for 4 hours. if i knew how to change gears i would because i have a trip coming up and im just going to tow it because i cant afford gas like that. when towing it should i take off the drive shaft? im leaving the back tires on the ground for the tow.
If its a stick shift you can just leave it in neutral. If its an automatic, you need to remove the driveshaft. Automatics rely on a large pump driven by the engine to make sure transmission fluid is getting to things that need lubrication and what not. Manual transmissions just rely on the turning gears in the box to move the oil around to where it needs to be.
 
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