46rh to 400, will it live?

Engine, Transmission & Driveline

  1. justthatguy

    justthatguy New Member

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    I've been high and low on the internet, and I can't really find a definitive answer. So, I'll lay it out here.

    I have a 73 fury, and I have a 400 that I am planning on 4 to 500 ft lbs of torque. I also have a 518 I was planning on using in my 71, but I think considering how nice and decently original that car is I am going to put one of my 727 stash in it, hooked up to a warm 360 magnum.

    My 73 also needs an engine, and I have a basically brand new 400 that will probably get a torque cam and maybe some higher compression pistons to fix the 8 to 1 problem. I would like to set this car up as follows:
    4 to 500 ft lbs at the flywheel, split the difference at 450 for a round figure
    4:11 or 4:56 final drive
    Using stock rockers in engine and possibly a/c so no high rpm here
    Possibly the Holley sniper efi with cable trans link
    Jvx(I think?) Adapter kit to hook a 518 to a big block
    Possibly a shift kit

    I'm not looking for speed or a race engine, I just want the car to swiftly accelerate with some semblance of fuel economy.

    I would really like to have the rear gear short, as it would help with the acceleration. With overdrive, it would basically be turning low 3.xx or high 2.xx engine speed with a 1 to 1 and that's exactly what I want. I'm not towing, and I'm not flooring it in overdrive.

    Will a stock 46rh live with a shift kit? Or am I looking at a hopped up 700r4? It's cheaper to buy a ready made 700r4 than it is to have a 46rh built it seems.
     
  2. C Body Bob

    C Body Bob Old Man with a Hat

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    Have you been over on FBBO ? I’ve read several threads over there over the years on the A500 & A518 swaps. Also MOPAR muscle mag has done some. MOPAR action too. Seems there is a company out west thinking Phoenix area that offered built versions. SMS trans or something. I doubt a stock one would last long.
     
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  3. monaco75

    monaco75 Senior Member FCBO Gold Member

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    The 47rh was put behind the 2nd gen Cummins trucks, and were able to take a little abuse. In stock form at that power level, I’m not sure if it will last very long. But should have no problems after a few upgrades/performance rebuild.

    in a heavy 3/4 ton truck at 500hp, the input shaft, output shaft, and stock converter start to let go. A car should not have as much effect, being lighter, but a c body is no pin up girl either...
     
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  4. Mr onetwo

    Mr onetwo Active Member

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    Valve body and shift points in Cummins 47rh are wrong for a gas motor. Some 47rh stuff can be used to upgrade a 46rh.There is a ton of info on the net about upgrading a 46rh.
     
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  5. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    46RH transmission has problems with the torque convertors failing. The lining on the locker fails and spreads abrasive friction material all over the rest of the transmission. This eats up the hard parts, especially the overdrive and bearings. That is one of the reasons these transmissions are so expensive to rebuild. There are some aftermarket convertors that are sturdier, but the basic problem still remains. You will also be defeating the whole purpose of the overdrive by going to 4.11 or 4.56 gears, your engine will still be beating itself to death at highway speeds. A better alternative would be to use an A 727 and add the gear vendors overdrive to that transmission. In that way you eliminate the problem with the mess made by failing locking convertors and you will save some significant funds on not having to by a big bell adapter to fit a 46RH. You will still need to modify the drive line and the rear transmission mount. You can run 3.55 gears with this setup and still have good out of the hole and highway drivability. As with any significant engine build, you will probably need a higher stall speed convertor and valve body modifications to match your new engine's torque curve to the transmission.

    Dave
     
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  6. CBODY67

    CBODY67 Senior Member

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    (Wondering whom the information source is that claims that much torque and that much gear is needed? Or are these just "talking points"?)

    Aren't there some tail shaft housing-to-floor pan clearance issues with the OD section of the A518 family trans?

    Just some thoughts,
    CBODY67
     
  7. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    On a C-Body it is a tight fit but it will clear the floor pan. The rear transmission mount can be fabricated to drop the tail shaft a half inch or so if needed without hurting anything.

    Dave
     
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  8. justthatguy

    justthatguy New Member

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    The source is me, I want that much torque. I want to not feel like I'm going to get run over merging on a highway. I'm really happy with 420 ft lbs in my 11 r/t charger, which is similar in weight.
     
  9. justthatguy

    justthatguy New Member

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    I'd really like a gear vendors but just the unit is more than I have in the entire rest of the project. I also would like efi and my old lady tells me it better have ac too, so I'm a bit shell shocked at cost already
     
  10. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    I feel your pain. Look at it this way, you will more than spend the cost of the gear vendor unit on a 727 the first time you have to rebuild a 46RH.

    Dave
     
  11. CBODY67

    CBODY67 Senior Member

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    The next question might be "What gear does the trans kickdown into at the speed you're getting on the highway?" Plus "What rpm is the engine at when that downshift is done?" Then, "Are you moving or stopped when you see that gap open up?"

    Reason for the questions above is that the rpm the engine is at during these kickdown activities needs to be an rpm where the engine is making power. With the "1-ton gears", I suspect the trans will be in the upper gears of any trans at the speeds you're moving. Not enough gear and you'll be at the lower end of the torque curve.

    Here's an example. A few times in the 1990s, I rented a couple of Chevy TrailBlazers with the SOHC 275 horse 6-cyl and THM700 automatic. There's an onramp on southbound I-35E in Dallas, which is shorter than normal (fine in the morning and evening rush hours as the traffic is not moving past 30mph, usually). The sight lines are not that good as it's on a curve, so "staging speed" can be critical. On the TB, if I slowed to 30mph to stage (slower than those behind me liked), when I saw a gap and hit WOT immediately, it would downshift into the 3.06 low gear and fly until it upshifted to the 1.74 2nd gear. But if I ended up staging at 40mph, (which more-pleased those behind me), then it downshifted into 2nd gear and the rpm was at the bottom of the torque curve . . . not good. So, to me, THESE are the dynamics which should be considered in the package you put together. Not specifically how much torque the engine has, per se, but at what rpm on the torque curve will the engine be at when all of this is happening.

    Not unlike the beloved "20 mph roll" during clandestine unapproved activities. If one car has a 4-speed automatic and the other one has a 3-speed automatic, when the time comes, the 4-speed automatic car will put the engine at a higher rpm for that initial jump as the 3-speed automatic car will likewise be in low gear, but a 2.45 ratio low gear rather than a 2.75-3.06 low gear. Plus the newer 6-8 speed automatics usually have a 4.__ low gear, with 2nd gear being close to 2.45. At least in the GM and Chrysler automatics. To me, if we put a small modern V-6engine in front of a 3-speed automatic, then we'd see just how much of their great performance is related to the many-gear automatic trans until the engine rpm gets higher on the rpm band, I suspect. Proving the old adage "If it won't go, gear it."

    Personally, I think it would be neat as heck to have an 8-speed behind the 383/330 in my "70 Monaco. IF the trans would operates as slick as the new 8-speeds do in the LX cars I've rented (both V-6s and R/T Chargers). Which is rated at about 425 lbs/ft of torque at 3200rpm. I suspect it would be a "new symphony" as the trans went through those gears at WOT, as the speedo needle headed for the triple digits.

    But to me, the real benefit of the 8-speed automatic is how it acts in normal street/highway driving. Never really putting the engine under load to speed up a bit or do an easy pass of slower cars . . . at less total throttle input than might be needed with a 3-speed automatic. Which made the old "part-throttle downshift" function so nice.

    Just some respectful thoughts,
    CBODY67
     
  12. furious70

    furious70 Active Member

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    You're not going to have 500ft lbs without significantly more work than described in the 400, so it'd be a moot point.
    I have an a500 behind my turbo 383. While I treat it pretty fair and it was built like a race 904 is, it hasn't failed me yet.
     
  13. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    A hi-torque cam, such as an RV cam will give you some added pump on the low end. If you are talking about a conventional flat tapped cam with stock valve gear it will start to run out of wind at around 4000rpms, well below the possible peak horsepower of the 400. You could also use an Edelbrock performer series cam, but with that option you are into having the heads ported for best performance and you would need to upgrade to adjustable rockers and better exhaust with a performance carb and manifold upgrade. There is no inexpensive way to get a 400 to anywhere near 500 ft lbs of torque. A stroker kit could get you there pretty fast but you are then into a build that will run you at least $7500. You should probably continue to do research to see what is available and at what cost to make an informed decision that fits how much you want to spend. You would want to also find out which crankshaft you have before doing any upgrades. A lot of 400 engines were produced with nodular iron shafts which are less than ideal for a performance engine if you are going to build something short of a stroker engine.

    Dave
     
  14. twostick

    twostick Senior Member

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    My buddy had a 518 behind a 484 Hemi. No problems. Good clutches etc and some diesel hard parts in the OD section I think.

    Kevin
     
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  15. justthatguy

    justthatguy New Member

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    It seems to me I'm probably better off with a 360 as just heads cam and intake puts those well into 400 ft lbs. I'm referencing Hughes engines here, and their junkyard build. If I was building a big block it would probably need to be a 440.
     
  16. justthatguy

    justthatguy New Member

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    The plan was something around 2300 to start building torque and peak somewhere around 3500. That's probably all it would ever realistically see hauling a car this big. I know the 5.9 can do it and I also know it's easier to assemble 5.9s to do it, more compression and better heads(I'm going to reference the engine quest heads here) out of the box on a stock ish rebuild. Plus they're easier to find and much cheaper than a comparable 440. Might be interesting to try a 6.4 hemi if the prices ever come down.
     
  17. justthatguy

    justthatguy New Member

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    I think probably the best thing is a 408 5.9 hooked to a 700r4. It's probably the cheapest way I can think to do it.
     
  18. cantflip

    cantflip Old Jagoff with a Hat FCBO Gold Member

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    Did you try 50mph?? A little tire squeal in a turn is nice sometimes. :lol:
     
  19. CBODY67

    CBODY67 Senior Member

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    The ramp and the feeder street were not long enough to do 50mph. It is on a rh curve, which limits visibility of freeway traffic. Maybe I needed more hormones and the TrailBlazer's high-feature SOHC 6 needed a small turbo?

    CBODY67
     
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  20. furious70

    furious70 Active Member

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    Not sure the Chevy trans has any advantage to an a500/42rh in your setup