9", or 12 Bolt?

Discussion in 'Got gears?' started by GRIMM, Aug 28, 2006.

?

Which differential would you prefer in a 3600 lb car with 700 hp?

  1. The Ford 9"

    42 vote(s)
    43.8%
  2. GM 12 Bolt

    54 vote(s)
    56.3%
  1. GRIMM

    GRIMM Well-Known Member

    8.8", 9", 10 or 12 Bolt?

    This is kind of a repeat, but i am just making sure before i go through with this.

    For a 3600 lb car (can go down to 3400 if need be), having 700 ish horsepower, which differential would be better, in otherwords which differential would you use?

    of course theyre both going to need to be highly modified either way.

    I have been quoted a price from the only company that says they have built a few 9's for 69 wildcats, 2.50 geard, nodular iron race case, 35 spline axles, disc brakes, built to my width and bolt pattern, priced at 3100.

    pick your choice and state why you picked what you picked.

    if you want, include the gear ratio you would choose for a 28" tire.

    thanks

    *************

    Well, with varying opinions i have decided to update this forum.

    I obviously added the 8.8" and 10 bolt, now i just need to find out how to add them to my poll.

    so, with more choices, anyone else want to vote or change their current vote?

    thanks
     
    Last edited: Nov 26, 2006
  2. oPh

    oPh Well-Known Member

    Might I suggest a Dana 70 out of Cummins Dodge. Factory 3.54 posi. Could weld upper control arm mounts on top of the cast iron Dana hsg, just as easily as could move them & reweld them on a 12 bolt housing. Either way would make for a uhh, quality hsg. :laugh: :laugh:
     
  3. 1973GS464

    1973GS464 Well-Known Member

    Currie enterprises will make a 9" for any car you need. Call them for a quote.
    Steve
     
  4. skylarkroost

    skylarkroost skylarkroost

    9" Ford rear is tough as nails. Plus gear changes are a snap. Whole pig just drops out after the axles are pulled.
     
  5. skierkaj

    skierkaj Day 2 Street Screamer

    I vote 12 Bolt . . . "Keep Your GM Vehicle All GM" :laugh: :laugh: :laugh:

    If it were my friend on the other hand, he'd vote for a 14 Bolt Chev rear, or 5 ton rockwells :shock: . . . but he's one of those monster truck folk . . . :laugh: :laugh: :laugh:
     
  6. iacovoni

    iacovoni The Buick.

    I just put a 9" in my car. Finished up last night, from start to finish, two partial days. If you want to go Ford, I can tell you how I built the same rear for alot less than 3k, more like a grand and that was with new 31 spline axles, 35 at no extra charge, cut and narrowed housing (bolted right in) with GM ends on it. This way I can still keep my rear brakes and wheels. Ebay is great. As for strength, go ford, plus they made a million of them for parts and so forth. Also, never worked on a 9" before (always been 10 or 12 bolt) it was the easiest rear-end I have ever put together, and if you ever want to change gear ratios/posi to spool or just maintain, go Ford, the design is so awsome. The GM rear-ends suck. I have only 425hp/500lb.trq, but that rear is not going anywhere.
    Just my 2 cents.
     

    Attached Files:

  7. Andrew

    Andrew Well-Known Member

    Hey Joe, Is that the housing sold on eBay from Quick Performance Racing ? If so, did you get all of the parts from them? Also, how did the drive shaft length turn out compared to stock? Seems like a steal.
    Thanks,
    -A
     
  8. oPh

    oPh Well-Known Member

    High torque loads are what kill r/e's, esp when the rears aren't designed or modified for those torque loads, & form of torque loading. How a rear is torque loaded, one might ask what is that. Let's put it this way, there is a difference between a built up rear which will take 500-700 ft lbs of torque footbraked, & one that will take same 500-700 ftlbs at 5000rpm behind a transbrake. Having built more than my share of 9"s, got to add, as in earlier post, I suggested Grimm's Wildcat would be best suited to receive a built up 9". As many others mentioned if it was closer to stock it would be fine with rebuilt 9 3/8 posi rear.

    Why a 9"... but not just any 9".
    - Late '60's Wildcats are heavy (I own a '67 & have performed resto work on two '68's), & again, simply put, a custom 9" is the easiast fab for such an application.
    -Grimm, you can conjecture a 3400-3600 lb late 60's GM big car, but what are the probabilitys this is going to happen in a Wildcat with steel body, roll up glass windows, an assembleage of an interior, a regular sized gas tank, & to make it strip legal, a quality built rollbar?
    -Again, there are no 12 bolts that will bolt up in the Buick Wildcat chassis, & the rear chassis is not easily converted to one of a '65-70 Impalla. Even a 12 bolt that could bolt up would need to have $1700 spent on it (in HD posi form)to endure the torque load of 700hp (guessing 600ft lbs of torque). For easiast 12 bolt attachment, sure, one could go ladder bars with a 12 bolt, & fit it to the Wildcat chassis, but one has to ask why, when there are better alternatives.
    -Back to earlier topic reply to Grimm, if one's smart, build with quality big bearing nodular case, daytona pinion support, & if mainly a street ride, a 35 spline soft-locker. There is no way such a 9" rear can be built for 1K. The 3rd member can't be built for that! Price the parts.

    Iacovoni, :Do No: Your reasoning astounds me. Sure one can throw a standard gray iron case, rebuilt 31 spline trackloc carrier into a homebuilt 9" housing & cobble it into the Wildcat. Could such a rear hold up to even 500 ftlbs of torque w/ sticky tires or slicks in a car that can hook, from my experience, bet not, esp at close to 4000 lbs. Gotta understand, have picked up the pieces from too many similiar weight/torque built A-bodys with entry level 9"s. The owners were so enamored by the 9"s drop out 3rd member design, but being CHEAP, would not spend the money on quality 3rd member componets. One gets what they pay for :rolleyes:

    Got Posi?
    :3gears:
    Roger
     
  9. iacovoni

    iacovoni The Buick.

    Yes, I did get the housing from QPR, I also had them order the axles from Moser. I did however had to throw the axles on a lathe to turn down the collars that were on them so I could use an axle seal. They recomended Black RTV, that to me sounded bad to me. Overall though all the parts and pieces fit perfectly, just make sure you give them the measurements you want or go with ones they have prefabbed for an A-body. The drive shaft will be too short (by about 2", just did not have enough engagement in the tranny for me) depending on your trans tail. I needed a new one anyway and got the Ford end put on it to make all parts meshed perfectly. I got the third member from Valley Spring for cheap. Parts are garunteed.

    And yes OPH, it all depends on what money and parts you throw at these things. The parts and pieces I research and pieced together will be (and so far ar) capable of withstanding the 500+ ftpds I am throwing at it. I have not thrown my stickies on yet, I will reply and give my results. My point was that 9's are really nice to work on, and if you need parts in a pinch, or really want a upgrade, they are everywhere. However, you do have alot more sperience than me, just going but what I have learned.
     
  10. GRIMM

    GRIMM Well-Known Member

    can a 12 bolt be built to sustain the power with around the same amount?

    im iffy on the whole 3% hp loss in the 9" gears, and then the 9lb bonus also...
     
  11. oPh

    oPh Well-Known Member

    12 bolts & 8.5 10 bolts can be upgraded to withstand low 9 sec passes. With over 550 horsepower & an adj 225 nitrous set-up, have local customer in the 9.70's on a well built 8.5 A-body rear. Similiar deal, have another customer in 3700 lb Buick knocking on the 9's with a bolt-in axle HD 12 bolt. Both have been running these numbers for years.

    Neither rear, or any 12 bolt, for that matter, will come close to bolting in a '69 Wildcat, so unless you are willing to spending some serious coin on rear chassis work, why even consider a 12 bolt???
     
  12. GRIMM

    GRIMM Well-Known Member

    Because im a GM man :D

    i guess the way ill be going is 9" then, what price would you say is reasonable for:

    case, nodular iron third member with daytona support, 3.50 detroit locker posi, good disc brakes, 35 spline axles with 5 on 5 pattern.
     
  13. GRIMM

    GRIMM Well-Known Member

    both differential companies i contacted said not to go with a 12 bolt.
     
  14. oPh

    oPh Well-Known Member

    The no 12 bolt response makes sense, am sure the tech reps understand the upper arm mtg problems if trying to go 12 bolt.

    Pricing will vary depending on who does the job. Back to earlier referall to a good local chassis shop. Most chassis shop builders fab & build a lot of 9" rears, & are a best value, if you are local. Many have accts with Strange, Mark Williams, Moser, & various disc brake kit suppliers.

    Just my .02, but IF a national 9" vendor like Currie, does not have a '69-70 Wildcat-Electra housing to pattern off of, then there's not much of a reason to even consider using them. If that national vendor does have a valid pattern to work off of, might be a good deal... just have to remember you're paying shipping. With quality rear disc set-up like the Wildwood big bearing Ford set-up, I'd bet high 2000's low 3000's is not out of the question.

    Got Posi?
    :3gears:
    Roger
     
  15. GRIMM

    GRIMM Well-Known Member

    ok, ill ill look around for a chassis shop.

    thanks for the help
     
  16. bobc455

    bobc455 Well-Known Member

    I assume this is a race-only vehicle?

    -Bob C.
     
  17. GRIMM

    GRIMM Well-Known Member

    wrong :D

    street mainly, very fast street.

    what we do with it, cruising on the weekends.

    But taking it to the track after this is going to be mandatory for my health!

    only occasionally, just long enough for them to forget my times and allow me to run without a cage, ill have to see what i can work out for a harness.

    now that i am planning on lower ratios, 3.50's probably, although im thinking as low as 3.40, what converter should i get since it will be used to cruise alot?

    cam is a TA 294-98F.
     
  18. bobc455

    bobc455 Well-Known Member

    The reason I asked is that the old rule of thumb is that although the 9" is stronger, the 12-bolt is more efficient. Maybe you don't really care about efficiency.

    -Bob Cunningham
     
  19. CTX-SLPR

    CTX-SLPR Modern Technology User

    I vote built 30-spline 8.5" 10-bolt. Impy SS's that are just as heavy if not heavier and making simular horsepower numbers are running on the stock 8.5 with a good LSD, welded tubes, aftermarket axles, and a TA cover. Its lighter and more efficient than either the 9" or 12 bolt, but it doesn't have the "top end" power capacity of them either. This is what I'm going to be putting under my 3800-4000lb '64 Riviera with a 700hp Turbo6 in it.
     
  20. GRIMM

    GRIMM Well-Known Member

    thats a possibility.

    reason i didnt/cant go with a 12 bolt is because it would be too hard/expensive to fabricate to make it fit.

    9 bolt is easier.
     

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