I've recently acquired an 84 Berlinetta that's going to be my new drag car. The car's previous owner put in a L05 350 and a TH350 trans. The car was running 16.70s the first weekend I put it on the track. I have brought it down to 15.90s with weight reduction and some tuning.

Traction is a huge issue, and the 60' times are currently horrible. The car has the factory 3.23 non-posi rear, and I'm shopping for a 4th gen posi unit to put in. While I'm doing the rear end swap, I want to do some rear suspension work. At the moment, this is my plan.

Box the upper/lower control arms and switch to polyurethane bushings
UMI torque arm/crossmember
Lakewood 50/50s

I don't have a whole lot of money to throw at this project right now, so I'm trying to save money by boxing the stock control arms myself versus buying aftermarket ones. The torque arm upgrade itself is going to take some careful budgeting for me to be able to afford but I'm pretty sure it's necessary.

Here's my questions:

How much difference is there between boxed stock control arms versus aftermarket units?
Is there any reason to upgrade the panhard rod, rear sway bar or rear springs? (I'm not trying to build a 10 second car here, I'll be happy with eventual 12s or 13s, and even those numbers are probably far in the future)
I thought I remembered seeing somewhere that the 4th gen rear ends came in a 3.73 version, but I was reading a thread here somewhere that said 3.43 is the tallest 4th gen rear you can get. Which number is correct?

Sorry for the long post and all the questions. I've been scouring these forums for awhile to get an idea of the setup I wanted to go with and these are the questions I haven't been able to find answers for. Thanks in advance for any help.

 

if you box the control arms well, there will be little difference between aftermarket units. mainly just looks.

panhard is only needed if you change the ride height.. doing a box on that will help any flex. sway bar if enough for your needs, just get some poly bushings. rear springs only need to be replaced if the stockers are soft and saggy.

not sure on the 4th gen rear but i'm sure 3.73's are available.. just search around when buying.

good luck on your build.

 

The highest a 4th gen rear came with was 3.42s I'm pretty sure.

 

Thanks for the answers guys. On the rear end gearing question, the RPO codes list a few different options:

GU2 Axle, Rear 2.73 Ratio
GU3 auto tranny,
GU4 Axle, Rear 3.08 Ratio
GU5 Axle, Rear 3.23 Ratio
GU6 Axle, Rear 3.42 Ratio
G80 Axle, Rear Posi-traction (Limited Slip)

Since the G80 RPO code seems different from all the others, might this be the 3.73 I'm after? Also, does this indicate that only cars with the G80 RPO code got posi rears?

 

<img src="http://images.highperformancepontiac.com/images/hppp_0809_08_z+trans_am+front_view.jpg" />

 

G80 is the op code for the posi unit and has nothing to do with gear size. 3.42 was the highest ratio you could get. This will be in a M6 car only.

 

I ran high 11's with a 3.27 geared 9 bolt. The key to traction is good tires. I was getting 1.7x 60' times even with the terrible gears.

The only increased strength between the fourth gen diif and the one you currently have is the larger axle size. If you're going to buy a new posi, buy one for your current diff for 28 spline axles and buy some aftermarket 28 spline axles to go with it. If you can find a 90-92 third gen, you can pull those axles and use them.

Both the third and fourth gen diffs have a tiny 7.5/7.625 ring gear. Both diffs are equally weak as the tiny teeth will break before anything else in the diff.

 

Cool, thanks again for the answers, guys. I guess that answers all of the questions I have on what parts to search for. Now that I've got my list made, it's time to start shopping. I'll let you guys know if my 60' times improve.

 

a cool pic. got those lcas real low