Will a Stock 489 handle 700hp?

Mopar Racers Forum

Have you had a stock 8.75, 489 hold up to 700hp while racing?

  1. Yes

    11 vote(s)
    28.2%
  2. No

    28 vote(s)
    71.8%
  1. flyfish

    flyfish C8H18+N2O = :-D

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    Sounds like the amateur back brace install warped the housing.
     
  2. pittsburghracer

    pittsburghracer FABO Gold Member FABO Gold Member

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    I voted no because 700 horsepower is hard on any rearend if the car is raced often enough. Not 700 horsepower and I’m not sure which 8 3/4 center section my son is running but he raced weekly running from 10.11 - 10.30’s for 3 years with zero issues. 3200 pounds, caltracks, transbrake use, and radial tires. Housing is not back braced, stock caps, spool, Doctor Differential axles, and 4.10 gears. He tried to put new gears in it every three years. His last set had three plus years on them and a racing Friday needed them for his 9 second big block footbrake car. They have 2 more years of limited racing on them and are still going strong. He hopes to update to a fab 9 inch in the near future. Neither car is probably near 700 horsepower but that’s not to bad out of what some consider a junk rearend.
     
  3. justinp61

    justinp61 Well-Known Member

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    I voted no because I broke the 4.30 gears in a 742 on the second pass my 408 hooked up. The car was 3240#, 727 and went 1.38 60' the first pass it hooked. The gear set had maybe 60 1/8 mile passes and a couple thousand miles behind a 340 that ran 7.24.

    After I went through the 727 making sure nothing was hurt the 8 3/4 was rebuild and the complete rear end sold. I mini tubbed the dart, then called Strange and ordered a new S-60. If I were doing it today it would have a 9" under it.
     
  4. 70DusterBob

    70DusterBob Well-Known Member

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    I agree with you 100%.

    Thanks
     
  5. 70DusterBob

    70DusterBob Well-Known Member

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    I'm planning on running the following set up:

    408 High Performance BluePrint Engine
    727 Race Trans
    Manual forward shift TCI
    8-3/4 Race 489 w/3:23's Duchman race axles
    I believe the tires are 235/50 series race radials.

    Plus, I am experimenting with a proto that increases low end torque significantly. I mean significantly.

    I was expecting not to have 700 on the top, but a lot on the low end which is harder on the diff than the 700 at the top. I have never heard of a diff breaking at the top, though I am sure it has happened, most of them break on the low end/take off.

    The 3:23's are for highway, this is a street strip car and the mileage is 8-9 w/o the proto on it. I can't go to 6-7 with race gears. I don't plan on racing it every weekend, but I need to prove that it decreases et's by so much. I plan on putting it on a chassis dyno. I don't know if I should keep it off the track and just do the chassis dyno with a professional tuning the timing/carb before and after the proto or if I will really need the et difference to sell it to racers.

    I am really good at vaporizing fuel, but I am not as familiar with all the ins and outs of racing parts, and how increasing the low end torque will affect the engine and drive train.
     
  6. Miszny

    Miszny Well-Known Member

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    9" has more parasitic loss, dana is the most effective rear end.
     
  7. pittsburghracer

    pittsburghracer FABO Gold Member FABO Gold Member

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    What the heck is a proto.
     
  8. justinp61

    justinp61 Well-Known Member

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    Prototype, maybe?
     
    • Agree Agree x 1
    • pittsburghracer

      pittsburghracer FABO Gold Member FABO Gold Member

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      prototype of what??? Lol. Must be a damn space shuttle
       
    • replicaracer43

      replicaracer43 Grumpy Old Man

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      Do a search on him...its comical.
       
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      • tjpatte

        tjpatte Well-Known Member

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        Yep, prototype carb thingy.

        Edit, repli beat me to it!
         
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        • replicaracer43

          replicaracer43 Grumpy Old Man

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          I wonder why hes asking about "700" horsepower, when now it sounds like he has a blueprint crate 408. No carb gizmo is gonna make that develop 700 HP
           
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          • pittsburghracer

            pittsburghracer FABO Gold Member FABO Gold Member

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            Gotta be like a top fuel blower to get 700 horsepower out of a blueprint engine.
             
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            • 70DusterBob

              70DusterBob Well-Known Member

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              Replica, you have no idea what I am working on. There has never been a great inventor that is main stream. Everyone thought Tesla was a nut, Einstein was a nut, and I am a nut. I take your criticism as a compliment. You can't understand this, I can't explain it because I need not disclose it. Of course you can't understand it, and of course I can't explain it. Some people criticize what they don't understand. Please understand that I am an inventor, and a bit unconventional at that. That is why I think of unconventional things, make sense?

              It works, and I am doing my best to get it officially tested to prove my findings.
               
            • 70DusterBob

              70DusterBob Well-Known Member

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              Nooooo, it doesn't get 700 hp. It gets almost 2x low end torque between 2,000 -3,000 rpm.
               
            • 70DusterBob

              70DusterBob Well-Known Member

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              I said low end torque is harder on a diff THAN 700 hp up top.

              Dang u guys
               
            • flyfish

              flyfish C8H18+N2O = :-D

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              Being a scientist myself, I'm curious. Please follow up weather it works or not....I can also say, it if does work you should move quickly to patent the tech and get the gizmo to market...if you don't, someone else probably will, even if it is a novel idea, others may be thinking the same thing and get there first.....I've had the latter happen a couple too many times in my days.
               
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              • justinp61

                justinp61 Well-Known Member

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                You got me there.

                Possibly this?
                 
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                • 70DusterBob

                  70DusterBob Well-Known Member

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                  The app is in the Office, thanks.

                  And boy does it work. As soon as I get a dyno sheet, I'll post it.
                   
                • replicaracer43

                  replicaracer43 Grumpy Old Man

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                  Actually I DO know, because you have posted about it here in the past. And despite your misleading post, a 8 3/4 should be plenty durable on the street with street tires in your car.
                   
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                  • 70DusterBob

                    70DusterBob Well-Known Member

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                    Well i don't know what you are referring to about misleading post but I advanced my tech and more is going on than before.

                    But thanks.
                     
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                    • replicaracer43

                      replicaracer43 Grumpy Old Man

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                      So your "gizmo" will double the torque between 2000 and 3000 rpm?
                       
                    • 70DusterBob

                      70DusterBob Well-Known Member

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                      Close to it. I can't say 2x as an absolute, I'm saying it is close. If you were here Grumpy, I would let you put one on your car so it would open your eyes wide and you would go "wow".

                      I have tried to be as open with this as possible. I have facts and data I can't share with you guys. You keep probing me for information, I asked simply if a 8-3/4 would handle 700 hp... I got a million answers, a million questions, and your criticism. I asked a simple question. Let me determine if a 8-3/4 would work... Hmm, nope. I believe now I need a Dana. According to all the replies I've gotten, 700 is around the hp where a 8-3/4 would break under low rpm, take off, which is where I was wanting it to be strong. If I had said I was working on a gizmo that produced 2x the low end and wanted to know if a 8-3/4 would work, I would have caught all this flack at the beginning. How many people have a diff rated at 500 hp and have broken it with a 500 hp motor? Or a 700 hp diff with a 700 hp motor?? I am producing more torque than a 500 hp engine will produce normally, I calculated to think that maybe a 700 hp rated diff would handle it, and perhaps it won't. I don't take chances and don't want to spent $2000 on a diff that is going to break. That's all I was asking.

                      You have your answer. I will post the results. Please let this thread die.
                      Thanks,
                      Bob
                       
                    • replicaracer43

                      replicaracer43 Grumpy Old Man

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                      Oh man...I cant let this go....I have a small block that makes like 455 ft lbs in that rpm range. Are you saying your gizmo will get me 900 ft lbs?
                       
                    • B3422w5

                      B3422w5 Well-Known Member

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                      A true 700 horse is 140 mph at 3200 pounds. And no, a 8.75 wont live at that power.
                      I broke mine the first weekend i started going 10.30’s with a new combination at 3350 pounds. 128 ish mph. That might be a true 600. That was foot braking
                      Unless the car is real light, doesnt make a ton of power, or both, you are on borrowed time
                       
                      • Agree Agree x 1
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