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Old 03-09-2005, 12:14 AM
RObs71Nova's Avatar
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Rear-end Setup opinions

Hello all. I have a 1971 Nova with a 475ish horsepower 454. Right now the car is running a completely stock 8.2 inch 10 bolt rear, but it's only a matter of time before it tears apart.

I recieved a 12 bolt rear out of a 71 Nova SS around Christmas time, and after finally saving my money I think I have the setup that I want. The only thing im stuck on is trying to figure out a gear for the car. After pricing them on summitracing.com, the 3.73 gear seems to be around 50 bucks cheaper then the 3.55 gear, and my gear selection was between these two. Would there be much of a difference in cruising RPMS between a 3.55 and 3.73 gear? I am running a 26 inch diameter tire, so the option of putting a slightly taller tire is there as well if need be.

The rearend as it is is a 3.07 gear open rearend. I wanted to change the gear and make it positive traction. Would these three things be all I need to accomplish that (besides the knowledge)?:

All these are summit part numbers
PWT-1910-LR Brand: Powertrax
Product Line: Powertrax Lock-Right Lockers
Aftermarket Carrier Style: Gear-style locker
Cover Bolts: 12
Axle Shaft Spline Quantity: 30
Manufacturer of Axle: GM
Carrier Material: Steel
Quantity: Sold individually.

Extreme traction output.
Differential, Lock-Right, Locker, 30-Spline, GM, 12-Bolt, Each

RMG-4900391 Brand: Richmond Gear
Product Line: Richmond Gear Ring and Pinion Sets
Ring and Pinion Ratio: 3.73:1
Cover Bolts: 12
Ring Gear Bolts: 12
Pinion Spline Count: 30
Carrier Series: 3
Ring Gear Rotation: Standard
Ring Gear Teeth: 41
Pinion Gear Teeth: 11
Ring Gear Diameter (in): 8.875
Pinion Shaft Diameter (in): 1.625
Quantity: Sold as a set.

Gear, Ring and Pinion, 3.73:1 Ratio, GM, 12 Bolt Car, 3 Series, Set

And Lastly

RMG-8310191 Product Line: Richmond Gear Installation Kits
Cover Bolts: 12
Ring Gear Bolts: 12
Pinion Spline Count: 30
Ring Gear Rotation: Standard
Cover Gasket Included: Yes Pinion Shims Included: Yes
Carrier Shims Included: Yes Crush Sleve Included: Yes
Pinion Seal Included: Yes Pinion Nut Included: Yes
Ring Gear Bolts Included: Yes Head Bearing Included: Yes
Tail Bearing Included: Yes Carrier Bearings Included: Yes
Axle Seals Included: No Axle Bearings Included: No

Is this all I would need to make the 12 bolt rear-end positive traction? Thanks in advance for everyones reply.

Rob

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Old 03-09-2005, 12:42 AM
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1.00 trans ratio, 26 inch tire, 60mph

3.55 = 2752 RPM
3.73 = 2892 RPM
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Old 03-09-2005, 12:11 PM
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Quote:
Originally Posted by montea
1.00 trans ratio, 26 inch tire, 60mph

3.55 = 2752 RPM
3.73 = 2892 RPM
With that tire and 60 mph in mind you would get the following also:
3.42 = 2651 rpms
3.07 = 2388 rpms

Yes the list of parts you gave will suffice, BUT you may want to rethink your gear ratio or tire size, factor in your transmission slippage and tire wear and you are looking at almost 3000 rpm's at 60 miles an hour.
A bit much for even a weekend cruiser and that size of engine with it's ease of moving a car of only 3400+ pounds, you won't notice the lower ratios being able to carry the car up to 60 as much as you will get passed on the freeway. A larger tire size will give the same effect as the higher ratios and your engine will be able to turn them just as easily.
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Old 03-09-2005, 07:57 PM
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I'm not that big on using a drop in locker if you are going to do gears as well. Stock carriers can sometimes be a weak point and when they go it is always bad! I would fork over the extra few bucks and get a full case limited slip or locker.
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Old 03-09-2005, 09:30 PM
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Thanks for all the feedback guys. I will have to do some more thinking on my gear selection, but I will probably pay the little bit extra and go with the 3.55 gears. Once again, thanks for the replys.

Rob
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Old 03-09-2005, 09:43 PM
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years ago

I used to run 3.31 geared 12 bolts in my 69 Camaro's with big blocks in them..... 427 to 482 cid engines

They really liked the gear for the street. These were all street cars.

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Old 03-11-2005, 05:54 PM
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you may find the help you need at
www.novaresource.com,,,,,,,,,then go to the links page,,,then the watson guides,,,,then the rear axle set-up guide.just to the left of that and at the bottom of the page you'll find all the rpm,tire size,rear end ratio's and all the calculators you need.i used it when i did mine.
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