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Old 01-14-2010, 12:38 PM
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Beefing up G-Body 1986 Cutlass Suspension

Hey everyone. I have a 1986 Olds Cutlass Supreme with a sbc 355 that is getting a new top end to the motor. The new motor should be putting out about 400hp/tq at the crank and is gonna be backed up by a 200-4R. The rear end is the stock 7.5" and has 3.73s. I am guessing about 325hp to the wheels. My dad put sway bars front and back, shocks, and springs out of a 86 monte carlo ss into it .I was wondering what weak links there is in the chassis and suspension. My dad said I should consider boxing in the upper and lower control arms. Is this worth the time and any other suggestions? Thanks! Also is the stock driveshaft gonna hold up? The new trans is longer so I either got to get it cut to length or have them build a new one.

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Old 01-14-2010, 03:06 PM
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Originally Posted by zildjian4life218
Hey everyone. I have a 1986 Olds Cutlass Supreme with a sbc 355 that is getting a new top end to the motor. The new motor should be putting out about 400hp/tq at the crank and is gonna be backed up by a 200-4R. The rear end is the stock 7.5" and has 3.73s. I am guessing about 325hp to the wheels. My dad put sway bars front and back, shocks, and springs out of a 86 monte carlo ss into it .I was wondering what weak links there is in the chassis and suspension. My dad said I should consider boxing in the upper and lower control arms. Is this worth the time and any other suggestions? Thanks! Also is the stock driveshaft gonna hold up? The new trans is longer so I either got to get it cut to length or have them build a new one.
I assume you mean weak links besides the 7.5" axle...

I'm not sure how you add a stock-style rear bar without boxing the lower arms. Certainly stiffening the arms will help the handling. Anything you do to make the chassis and suspension arms less compliant (so the shocks and springs can do their jobs) will help.
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Old 01-14-2010, 03:38 PM
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There are tons of G-body suspension parts available, how much do you want to spend?
BMR Fabrication, Hotchkis, Edelbrock, Globalwest and many others.
There are bolt in 9" ford diffs, brake upgrades, pretty much what ever you want is available.

I had a 80 Monte with a pretty stout 355 and a 200-4R with 3.73's it was a blast to drive.
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Old 01-14-2010, 04:18 PM
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I would definitely box the upper and lower control arms, and do some polyurethane bushings at the same time. The 7.5" rear is definitely the weakest link though, but as the above posters pointed out, there are many bolt-in solutions, or if you're handy with a welder, you could do a 9" yourself as well.
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Old 01-14-2010, 08:42 PM
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I can get a 9" ford housing with axles for like $700 I would just have to get gears and a center section. Will the rearend hold. Im only gonna be making like 325hp at the wheels.
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Old 01-15-2010, 05:25 AM
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It depends on how well it hooks up.
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Old 01-15-2010, 05:41 AM
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Originally Posted by zildjian4life218
I can get a 9" ford housing with axles for like $700 I would just have to get gears and a center section. Will the rearend hold. Im only gonna be making like 325hp at the wheels.
With decent axles and center section, it should hold up to a lot more than that. You could probably beef up your stock rear to stand up to that much power. Upgrade the axles, weld the tubes to the center section and add a girdle cover and you're there, but it would be pretty much maxed out at that point. A 9" will give you "room to grow", so to speak.
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Old 01-15-2010, 10:07 AM
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I will def consider getting a hold of a prefabbed 9". How hard is it to cut, chop, and weld the rear end to fit. My neighbor is one hell of a machinist and makes all sorts of crazy stuff for his race car. If I could buy a 9" housing and then give him a couple hundred bucks. We would have to cut the axle housing to the correct length. And then weld on 4 places for the control arms to hook up to. Doesn't seem like it would be crazy hard to do just have to make sure everything is straight. What is the approx hp limit for the gm 7.5" axle?
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Old 01-15-2010, 10:22 AM
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You really need a jig for narrowing the housing, to make sure it's straight. I know guys running as much as 450 fwhp on S10 (7.625", 28 spline) rear axles, but they cross their fingers a lot,
Up to about 350 rwhp, no trans brake and no slicks, you're fairly safe.
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Old 01-15-2010, 11:42 AM
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Alright sounds like I will just have to keep street tires on the back until I get a chance to put either an 8.5" GM rear end or a ford 9" in it. But for now it seems like pulling out the control arms and boxing them in will be the best to do.
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Old 01-15-2010, 12:25 PM
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Yep, and the best part is that's pretty cheap to do. Urethane bushings are a good idea as well, if you can afford to do them at the same time. The boxed arms and bushings should give you considerably more decisive handling and traction, especially if you've got rear sway bar on there.
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Old 01-15-2010, 01:02 PM
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My dad did urethane bushings a while ago. The car does have some wheel hop every now and then when you do burn outs.
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Old 01-15-2010, 03:25 PM
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You can also buy prefabricated GM 12-bolt housings to fit right in there from several sources too.

The rear sway bar for my Malibu came with spacers to fit inside the original lower control arms, all factory original pieces. The most common cheap fix for the strength upgrade of the lowers is to tack-weld pieces of pipe inside the arm to prevent the arm from getting crushed by some torque happy person installing the swaybar bolts, then welding a piece of 1/8th inch flat steel to the open area of the control arms, and make sure you complete the job by making sure the bushing ends are welded to the added piece of steel.

Another commonly used strength add-on for the 7.5 inch axle is to drill and tap the ring gear bearing caps, and housing for larger/higher strength bolts, then you can also add to that modification by purchasing a cover with the bearing preload studs and nuts to assist in spreading the load to the housing better.

Another thing I have seen a lot is mark your axleshafts and prep them to paint a stripe the length of the shaft, Many racers do this to check how much their axleshafts have twisted, I have seen pics of up to nearly a full revolution of twist without them failing- and they were reported to be stock shafts.
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Old 01-15-2010, 05:46 PM
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Now what is the price difference in after market support from the ford 9" housing to the gm 12 bolt?
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Old 01-15-2010, 07:25 PM
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Quote:
Originally Posted by zildjian4life218
Now what is the price difference in after market support from the ford 9" housing to the gm 12 bolt?
The 12-Bolts for G=Body are aftermarket only and aren't cheap. Check with Moser, Strange or Currie.
If you install a OEM GM 12-Bolt you'll need aftermarket Upper Control Arms as the mounting angle is different.

G-Body Rear Swaps >> http://www.maliburacing.com/tech_rearend_swaps.html
G-Body Tech>> http://www.maliburacing.com/tech.html
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