rear end suggestions for 550-600 RWHP in a 72 cutlass

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krom
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rear end suggestions for 550-600 RWHP in a 72 cutlass

Postby krom » Sun Mar 27, 2016 3:53 pm

building a 72 cutlass with a 5.3 ls, 4l80e, and single turbo.
Stock rear is a 8.5" with 2.73 gears, and open diff ("SAB257 2" stamped in it)
car will be street driven, on street tires (around 305 40 18 planned size, havent tried to fit one yet though) and probably never see a real drag strip,
this is a budget build, believe it or not (I have less than a grand into engine, tranny, harness, ecu etc)

I'm looking for some suggestions, and prices.

put a posi and gears into stock rear, cross fingers. $500-$800
find a used 12 bolt, with 3.73 and posi $1k-$1.5K
Go all new 9" $2k-$3k

Am I missing something?

Is there any chance the stock rear would live through any abuse?

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monzaz
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Re: rear end suggestions for 550-600 RWHP in a 72 cutlass

Postby monzaz » Mon Mar 28, 2016 12:36 am

The Original 71 72 Skylark Cutlass rears are more that acquitted to handle that power.

Recon GM posi G80
Better idea would be a good aftermarket unit (If the car is a keeper)
You have overdrive so 3.73 would be a good ratio (we have good used gears if you are keeping the budget idea and since no drag racing is going on)
Bearing and seal kit would be a great idea as 45+ year old bearings I assume as 2.73 sounds like original equipment.
Find a GOOD shop to install the parts THAT IS the biggest deal to keep things ALIVE!

Jim
J D Race
PM for prices
J D Race

krom
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Re: rear end suggestions for 550-600 RWHP in a 72 cutlass

Postby krom » Tue Mar 29, 2016 8:54 pm

The install is the thing...

I do marine work, have rebuilt plenty of lower units, and out drives I've been to a couple factory training seminars on setting up lower unit gears, but that is using all the correct tools. Everything is done by measurement, there is no pattern verification done, if everything measures ok, and the rolling torques are ok, its considered good. I don't know of a local shop to use, and haven't ever seen a good gear pattern (or a bad one) in person.

What diff do you recommend?
Will a detroit with light springs be miserable to drive? clunky in a parking lot isn't a problem to me.

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monzaz
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Re: rear end suggestions for 550-600 RWHP in a 72 cutlass

Postby monzaz » Wed Mar 30, 2016 12:03 am

We have Power trax units but are for 30 spline axles... 30 spline axles for a 8.5 bolt in axle rear will be quite expensive at 370.00 a pair BARE.

A detrouit locker will be pretty expensive again 500-600 for a unit alone.

I am not really worried about HP Torque is what breaks parts... If your only in the street 1000 hp is not big deal... The street can not hold BIG HO or torque so the tires break loose and there is no pain on the rear components...AT THE TRACK is where the HOOK ias and parts will fail. So where is this vehicle going to be at most of the time?

IT all really does not matter as the spiders will be your weak spot any rear you build.

Detroit locker is not budget.... Moser race axles is not Budget. Good thing the rear has got going for it is the BOLT IN AXLES and the ring and pinion will be big enough to hold the power - You have to choose a posi unit to do the job.... Again you said street drive so any Aubrn Eaton will do the job... No Grip, no breakage.

Jim
J D Race


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