8" vs 9"

Discussion in 'Technical' started by Jason M, Jan 26, 2004.

  1. Jason M

    Jason M Hibernatin for the Winter

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    Just read in another post that the 8" is not quite as stong as an 8.8" and I realize a 9" is way better and parts are definitely easier to get for the 9" rather than parts for an 8". But in all fairness the is the 8" that much weaker? I realize if your running gobs of horsepower your gonna want a 9" rear-end. But what kinda life can you expect out of one running a mild 302?

    My main reason for asking is because I want to put a mild 302 into my car this year and I just had the 8" rebuilt with 3.55's and a Auburn Locker (last one in stock the place had...... been on the shelf a few years LOL) The only thing I didn't replace were the shafts cause I don't have the kinda money Mavaholic has to put moser ones in (I read the article long before I ever came to this website Dennis) I would have loved to though.......

    BTW I have a heavy foot and like to mash the throttle at times, so would I have been better off putting in an 9"? It would have cost me more in the long run and I am sure it would have been worth it but if I am only going to be running a mild street machine and maybe the occansional trip to the strip. A 8" should be able to handle all this right?
     
  2. mavman

    mavman Member

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    as long as you have an automatic, less than 500 HP, and street tires, the 8" will last a long time. They're tougher than people give them credit for. The weak link is the pinion. I ran one behind a 420 HP 302 for ages with 10.5x28 slicks, dad ran the exact same rear in his fairmont for a few years (same rear end...I went to a 9"). Also have one in the street mav--which at one time made over 500 turbocharged HP and a ton of torque. It's still together as well, even with the stock 2.79 gears. I did swap to 3.55's once to run it at the strip, but swapped back to the 2.79's as they are better for that much power. Besides, the max rpm with that motor was 5500. It would peg the speedo in 2nd l:D
     
  3. don graham

    don graham MCG State Rep

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    feb. 2004 issue of super rod magazine says "if your running under 500hp on the street, you really don't need a 9 inch. ":)
     
  4. CometGT1974

    CometGT1974 Gearhead

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    Yea, the 8" is actually quite strong but don't listen to everything that you read in magazines. One article in Hot Rod said that anything over 300 hp. is too much for an 8"!! :rolleyes: I went in the 6's in the 1/8th several times on my old 8" and I think John Ford is still running his 8". I think alot of it has to do with weight, our cars are on the light side so the 8" will last longer than if it were in a heavy car. Once you get up to around 500 hp I think you're rolling the dice!!
     
  5. Thack

    Thack vision advicator

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    I have broken the 8" twice in my mustang. I have stuck with it becauase I had the alburn pro and didn't want to waste it. My mustang weighs 3110 lbs and makes 308 RWH 346 RWTq

    The first brake was from me not having my under ride traction bars on. The rear wheels hoped and killed the rear but, left a cool looking design on the rear end housing. The second time was shifting from first to second spanking a BMW m5.

    I have always broke the ring gear caps, on this last rebuild I used ARP stud kit and haven't broke anything sence it's been four yrs now.
     
  6. Mavaholic

    Mavaholic Growing older but not up!

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    I dont have money, I have credit!!!
     
  7. T.L.

    T.L. Banned

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    The Ford 8-inch is stronger than a GM 10-bolt...
    :D
     
  8. bmcdaniel

    bmcdaniel Senile Member Supporting Member

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    It makes a big difference if you have a light car and/or tires that will turn over easily rather than slicks or really wide tires. If the tires can spin they bear the abuse more than the rear. But if they hook something else has gotta give.
     
  9. CornedBeef4.6L

    CornedBeef4.6L no longer here

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    Having run a MAE posi unit for 3 years in an 8inch I feel they are reliable. MOtre reliable than 5.0l blocks from what I have seen and experienced. Good Luck. Upgrade the axles comes recommended have twisted one at the splines but other than that she is doing just fine,
     
  10. PINKY

    PINKY .....John Ford.....

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    I have a 9" in mine, but I am running 28 spline axles. I have 1.39 sixty foot time(Once) and regular 1.40-1.41 all day long with no trouble at all. I also run a mini-spool(which is not the preferred choice) but until I break it, I will continue to use what I have.
    Weight has alot to do with the longivity of parts, my car is kinda light, so that helps a bunch. Also, I do not run a trans-brake, which would destroy my set-up I have right now. But it would be cool to put it on the back bumper.........once.
    Those little 8" rears can and will hold alot of power, its just like everything else, if you build it right, with the right parts it will last.
     
    Last edited: Jan 27, 2004
  11. Mavaholic

    Mavaholic Growing older but not up!

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    OK, I'm not a automatic guy, so what is a trans break and why is it so hard on the rear?
     
  12. PINKY

    PINKY .....John Ford.....

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    A trans-brake is one of the coolest things ever created for drag racers........
    I do not know mechanically how it works....something in the valve body or something......
    anyways, what is, is you have a button(momentary) that when it is pressed(it activates the transbrake) and that causes 1st gear and reverse to lock together.
    So, with the button pressed, you mash the pedal, and it will set there and bounce at whatever rpm you have it set for(2 step). I know guys that have it set for 7,000 rpm. So there setting there at 7,000 with the pedal to the floor, let go of the button(transbrake) and reverse disengages, your rpm limiter is deactivated and all of the sudden you have just launched at 7,000 rpm........AMAZING!!!!!!!!

    Thats why you see some of them cars with the front tires 5 feet in the air. Almost ALL of your "super stock" guys run them cause you have to meet certain engine, tranny and chassis specs/regs its a easy way to go faster.
    I have been told I could easily get into the 6.30's with transbrake, right now I am at 6.55 on foot brake..........but as you can imagine, its hard on parts and your tranny and I do not have the "stuff" for that kind of abuse............yet!
     
    Last edited: Jan 27, 2004
  13. CometGT1974

    CometGT1974 Gearhead

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    John, when you do decide to get a T-brake call JPT up in Michigan. The absolute best on C4 tranny's.
     
  14. bmcdaniel

    bmcdaniel Senile Member Supporting Member

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    With a trans brake the rear suspension is unloaded while the engine is reved at the line. It's a real shock to the rear when you let it loose. When you rev on the foot brake the suspension is already loaded and you don't get such a drastic launch.
     
  15. Jason M

    Jason M Hibernatin for the Winter

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    So what I am getting is that my 8" will probably handle anything a mild 302 can dish out, I am glad to hear that. I wasn't trying to be rude or anything Mavaholic.... just priced out a set of those axle shafts you have in the 73 Mav you have and I decided for the price I would take the chance..... unless I had motor like yours. The whole reason I wanted my great grandfather's Mav was because of your car.
     

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