84-Z28-Canada

Hi folks, wanted to ask everyone's opinion. Car is currently running a 383ci small block, decent cam, heads, etc. Has a best ET of 12.98 at 105 mph. Last season I swapped from my stocker 10 bolt 3.23 open diff and drum brake to the BW 9 bolt with a 3.27 posi and disc brake. Was a good bonus, the posi helped with traction and finally got into the 12s. Here's my dilemma. Everything for the 9 bolt is either unavailable, or costs way too much. Now I know everyone is going to say don't spend money on either of them, just save up and buy a good bolt-in S60, 9 inch, etc. I know, but I'd like to make an improvement for this season. So I'd love to hear opinions on two ideas:
1) The only available ring and pinion upgrade for the 9 bolt is a 3.70 gear. Do I just go ahead and install that, and see what little improvement there is, or...
2) I still have my 10 bolt diff. Do I get a mini-spool, 4.10 gears, and c-clip eliminators, and then run that. It's near the same price as trying to get gears for the aussie 9 bolt

My goal is to get up to a 4.10/4.11 gear, something like that. I went up to a 27" drag radial for the traction, so I need to compensate with a better gear ratio to get my ETs back down. Let me know your thoughts. Thanks,
Ian

AlkyIROC

Doesn't matter what you do to the 9 bolt or 10 bolt. They will eventually fail and money invested will be lost. Just start saving for a direct bolt in 9" housing. You might be able to pick up a used center section locally. Most of the aftermarket 9" housings are designed for the late model disk brakes but just about any set can be adapted somehow. You don't need to spend $4000 to put a 9" under the car. Knowing where to get parts from can easily keep you under $2000. I think the bare housing with axles is only around $1000. A junkyard center section with a posi in the proper spline count may be a couple of hundred. Brakes depends on what you have and how much do you want to spend. There's a sticky in the brake forum about putting GMC Jimmy rear disk brakes on a 9" that I did many years ago.

articwhiteZ

iTrader: (56)

like you know ..what w are going to tell ya..BUT.. you can drop your et and pick up a few MPH.. with the 4.11.. give it a shot..just remember... the only thing ya have to add is the gears..dont fall into the trap of rear end cover that push on your caps.. or axles.. as the first thing to brake is the Pinon gear teeth..then after ya brake a few..save up and move on..never look back..

LB9GTA

iTrader: (1)

I took my gm 10 bolt to low 11's.
Diff girdle and welded the axle tubes.
It eventually popped.

Save the money for a good diff, or keep putting a band aid on what ya got.
In the end, it's cheaper to go with a 9"
I have a quick performance 9"

84-Z28-Canada

Thanks for the opinions guys, keep em coming. I guess what I'm saying is.. I know they'll both break. I just want to go a little faster in the mean time. My plan is to get a bolt in GM 12 bolt or 9" from Bear Performance in Windsor in the next few years. I guess the other option is to leave it alone and float around 13.00 in the 1/4 mile, but like all of you, I'm addicted to the ET gains. Ultimately, let's say I have a $500 budget (C$) that I can put into either rear end. That means either: 3.70s in the 9 bolt (which has posi, bolt in 28 spline axles, and disc brakes), or a 4.11 and a mini spool in the 10 bolt with drum brakes. Not afraid of swapping the rear ends, just unsure of whats the better bang for the buck of those two things. Thanks again

skinny z

I broke the BW 9 bolt making my first pass in the 12's. 3.70 gear set and the pinion lost a couple of teeth. Installed a 3.27 gear and ultimately went faster and it held up but I've hardly got a powerhouse and traction was always limited. That broken pinion was a result of relatively decent slicks, good track prep at Grand Bend and dead hook. 1.71 60'.
Personally I wouldn't invest in the 9 bolt for the reasons you mentioned and the fact that I broke one with limited power. Besides the obviously good advice given here regarding a 9" or equivalent, you can probably enjoy a season of racing building the 10 bolt as you suggested. Brace it as best you can and hope it holds up. BUT, be prepared to say goodbye to your investment as more than likely it'll let go.

84-Z28-Canada

That's good insight Skinny, thank you. Maybe the thing to do is just be happy with the ET for now, and leave the rear alone til I can afford the big one. Also, I guess by switching back to my stock size drag radial I'll gain back some of the gear. I don't know how much I gained by switching to the bigger tire anyhow when it comes to traction, and my burnouts suffered. Just typical bench racing during the winter month blues! Money is maybe better spent on something else til I can get the big diff.

AlkyIROC

Well comparing the 9 bolt to the 10 bolt...

My car originally had a 3.27 gear 9 bolt. With 26" tall tires, I pushed it into the high 11's but gearing was all wrong. I was starting to pull into the powerband at around 900 feet. I swapped out the 9 bolt for a 10 bolt to get a better gear ratio. Did 4.10 with 27" tall tires. Spent all the money to do all the good upgrades including aftermarket 28 spline axles. Did a welded spiders type spool since it wasn't street driven. Got down into the low to mid 10's. Swapped out the transmission for one with a transbrake and did a diff swap to a 9" at the same time. I knew the tiny 10 bolt wouldn't withstand a transbrake launch.

Almost destroyed the factory 9" center a few years later. I pulled the pinion out to fix an oil leak and found the support bearing housing was cracked. If the pinion support housing breaks off, it will spit the pinion out the side of the diff. I was running high 9's at that time. Swapped out the factory case for an Aluminum Moser bolt through housing and never looked back.

skinny z

I'm pretty much in the same boat. At 108 MPH trap speed, I'm barely 5500 RPM and haven't hit peak HP (by my reckoning) at the stripe. The latest iteration of the 350 has a decent sized cam and I shift at 6500 from 1st and 6000 into 3rd. Getting to 6000 at the top end would be real improvement. And the 26" tall ET Streets, as old as they were, didn't give the traction I needed especially considered the more or less street shock setup I have. About the only tuning tool I have are air bags which do make a difference but don't do anything for weight transfer. With the old tires, 60' times rose from a 1.7 best to a 1.8-1.9 average. The new converter will only make the launch a little harder to control but I've yet to test that as other car problems are keeping me from the track. Maybe this year...? But I doubt it. New engine (shortblock) and exhaust are needed and there's probably not the budget for that (considering the money pit house I bought and am renovating).

AlkyIROC

I was 12.0 at 112 MPH. A normal 12.0 car runs around 118-120. I would be slow off the line paired up to another 12.0 car but could catch up and pass them at the finish line. Drivers told me I was hard to race against because they couldn't judge me closing in at the finish line.

Beeman

My rear is from a 71 Torino and when I bought it someone had transferred the brackets from a stock rear to it. I could use the stock lwr arms and the coil springs. It was set up as a 3 link so it had brackets on the top for an upper arm. The car it came from had a cage and they tied the upper arm to it. If you find a correct width housing you can swap the brackets over and Quick Performance makes a torque arm bracket you can put on the 9". Just do it once and be done with it.