9 inch or 8.5

[AThorpe]

Got an 83 monte plans for 350 sbc 6-71 blower afr heads .555 solid roller cam 3000 stall th 400 with trans brake 600hp n/a nitrous 750hp
Should i go with a 9 inch or 8.5
Found a stock 9 inch for $350 but gotta weld on brackets About $200 can find gears and spool for cheap on Racingjunk.com for around $200 Some where $700 total
Found 70 chevelle 8.5 rear for $50 its an open diff
get swap kit for $350 can find gears and a posi for $200 total $550
what do u think? will axles hold up

 

[supercrackerbox]

The problem you'll run into is that neither of those rears are the correct length for a G-body, so you'll either need to have it shortened/lengthened, or you'll need custom offset wheels.

Another thing to consider is if your local track will require a C-clip eliminator kit. That will be an added expense for the 8.5", but the 9" doesn't use C-clips.

As for the stock axles, I don't know. Gear ratio and tires will have affect that outcome. But if you break one, then you know to upgrade.

 

[AThorpe]

the length isnt the problem the 8.5 is 58.5" for that year chevelle and the 9 inch is 58" i might side with the 9 inch because of the c-clip eliminators ad some gears and a spool and some axles should never have to deal with it again. But then again Ive read on many occations about power loss with the 9 inch over and 8.5

 

[pontiacgp]

Another thing to consider is if your local track will require a C-clip eliminator kit. That will be an added expense for the 8.5", but the 9" doesn't use C-clips.

I would never use c-clip eliminators on a 8.5 or 7.5 cause they leak gear oil and nothing will stop them from leaking....

 

[shotgun]

I run a stock width 68 12 bolt in my 78 Cutlass.

The rims are not really custom, just a different back space.

If you run slicks you are required to have aftermarket axles wether it is a GM or Ford.

I also run C-Clip eliminators on the 12 bolt and never had any leak. The rear has been apart for gear changes and the eliminators were reused.

I would suggest have the axle tubes welded on any GM rear. When the 2 plug welds give it is ugly!

Is the rear an 8.5 or 8.2?

 

[JESSE]

9 inch

it sounds like your going drag racing, if so i'd put a 9 inch in for sure...

i don't know if you ever raced a gbody, there' a lot more to hooking one
up, check out the forum for[ hooking up a gbody] lots of good info there
jesse

 

[pontiacgp]

shotgun.....which brand of c clip eliminators do you use and are you using OE axles? We have never used them because of all the complaints we have heard from the other pits that they leak. One guy in our shop tried them on a 2nd gen camaro rear end and he tried everything to stop the leak.

 

[shotgun]

Jesse, where's the new N2O results???? 😀

The axles and eliminator are from Moser.
Maybe using stuff from the same manufacturer helped? Also a light bead of "right stuff" and I am dry.

Spools also require aftermarket axles regardless of class or et per NHRA.

Also quicker then 11 oh reqardless of posi type require aftermarket axles.

So a 15 second car with a spool still needs aftermarket axles!!

 

[pontiacgp]

thanks for the info...we have to keep the with the OE rear end and although we could upgrade the axles the stock axles don't give us any problem with our circle track car. We can use a spool but we weld the spider gears instead and that's never failed. We try to use our sponsors money on getting us upfront and as you know all the little things add up quick.

 

[NAILS]

Got an 83 monte plans for 350 sbc 6-71 blower afr heads .555 solid roller cam 3000 stall th 400 with trans brake 600hp n/a nitrous 750hp
Should i go with a 9 inch or 8.5
Found a stock 9 inch for $350 but gotta weld on brackets About $200 can find gears and spool for cheap on Racingjunk.com for around $200 Some where $700 total
Found 70 chevelle 8.5 rear for $50 its an open diff
get swap kit for $350 can find gears and a posi for $200 total $550
what do u think? will axles hold up

first off- are you sure its a 8.5 and not an 8.2 ? im almost sure of it that the 8.5 never came in the chevelle... the 8.2 did though. ( correct me if im wrong ) if it is infact a 8.5 rear, grab it - sell it for 800-900 and buy a nice 35-36 spline currie or moser rear end assembly for 1500-1600 ( you estimated to spend 700 all said and done anyway. ( and if you do that you wont have to spend money on axles either ) also. nobody on racing junk will sell gears and a spool or gears and a posi for a ford or a gm under 300 bucks. but if you can find it by all means jump on it.
if you are going to be using this car for drag racing, keep in mind the significant difference in weight between the 2 rears. the 9" ford rear is 40-45 lbs. heavier than a gm 12 bolt rear which is a bit larger the 8.5 - id say off the top of my head you about 75-80 extra lbs in a 9" over the 8.5
i personally like both the 9" and the 8.5 - however id take the lighter one. the 8.5 is by no means easy to break. plenty of g body guys go high 8 sec using a well build 8.5 ( stock suspension and drag radials no less ) without problems. mean while with the 8.5 you have a slew of gear rations to choose from, and after market parts to use. the 9" doesnt offer a huge selection of after market parts and upgrades. a con next to weight for a 9" is the pinion position in the center section. it sits almost 2.5" below the ring gears center line. that results in loss of horse power caused by friction reduction. i believe the 8.5 pinion gear is only 1.6 or 1.7" below the ring gear center line. in comparing posi- the 8.5 uses an eaton posi which is stronger than the ford posi ( so every published comparison concludes ) however i am skeptical due to the spider gear count- gm has 2 while ford has 4 gears. i can only assume that the 4 gears will be stronger... but thats my .02 good luck either way