BB 727 to A518 Conversion

Discussion in 'Transmission and Drivetrain Tech' started by carfreak6970, Nov 14, 2017 at 7:52 AM.

  1. carfreak6970

    carfreak6970 Well-Known Member

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    Hello,

    So when I get bored at work I peruse eBay Motors and craigslist to see what vehicles are out there. I came across a 76 Charger that was fairly optioned out, in nice condition that had a 400 2 barrel on it. It checked all the boxes of a vacation road trip car: A/C, power windows, cruise control (yes I like to be pampered hahaha), and just all around different. But this got me thinking.

    With this being a big block, it complicates a transmission swap to the A518 since I believe the A518 never came attached to a big block. Now I know they make bell housings and adapters to adapt the A518 to a big block. But since the A518 is essentially a 727, couldnt you remove the guts from a big block 727, and install the tail shaft and the innards of the A518? That way you can get the over drive and possibly the lock up torque converter

    I know there will still have to be floor modifications and the drive shaft would have to be shortened, but shouldnt the cases between the two be the same with just a different bell housing?

    This is just brain storming to calm an idea I had this past weekend hahaha

    Thanks
     
  2. KickDown

    KickDown FABO Gold Member FABO Gold Member

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    Unfortunately it's not as easy as that. But what a great thought!! Essentially you are correct that the basic housing will accept some of the 727 parts. Where the cases differ is at the rear where the OD housing bolts onto. With the 518 housing there is a recess for the OD Clutch piston, also the govenor support is way different. You will also need a different flex plate if I remember correctly. Rusty Rat Rod is the Guru on the 727/518 conversion. He will point you in the right direction.
     
  3. carfreak6970

    carfreak6970 Well-Known Member

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  4. replicaracer43

    replicaracer43 Old school member

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    I believe someone makes a bellhousing to put the 518 behind a big block. Basically you cut off the factory bell, and the new one attaches with the front pump bolts, I "think"
     
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    • carfreak6970

      carfreak6970 Well-Known Member

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      replicaracer43, you are not incorrect. I have seen those before. But if I would go through with this swap I would rather not have to slice up a transmission case.
       
    • RustyRatRod

      RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

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      Now that I don't know, but @Bighead440 can probably tell you.
       
    • Bighead440

      Bighead440 Member

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    • RustyRatRod

      RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

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    • 67Dart273

      67Dart273 Well-Known Member

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      The case is substantially different. The OD models have additional passages, and they are even different I believe, between the RH (hydraulic) and RE (electronic)
       
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      • rumblefish360

        rumblefish360 so close yet so far away

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        I think the bell housing removal to weld on a new one is the “Ultra Bell” set up.
         
      • TrailBeast

        TrailBeast Slightly Twisted Member

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        I think Del covered a lot of it in post 9.
        I think you would find that it would be a lot easier and lest costly to add an aftermarket OD to the big block trans.
         
      • replicaracer43

        replicaracer43 Old school member

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        I think it bolts on after you cut the old bellhousing off, but "ultra bell" does seem to ring a bell, hahahaha
         
      • replicaracer43

        replicaracer43 Old school member

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        You think you can add a aftermarket OD cheaper than the cost of a 400ish dollar bellhousing? Do tell......
         
      • rumblefish360

        rumblefish360 so close yet so far away

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        Well, I don’t know about any of this but if I had nothing to start, it would be the adapter (JVX) and the trans (518) and what else???
         
      • 67Dart273

        67Dart273 Well-Known Member

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      • RustyRatRod

        RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

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      • jas0162

        jas0162 Well-Known Member

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        I
         
      • jas0162

        jas0162 Well-Known Member

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        oops. I bought the J and W bellhousing and installed it on a 518. I think it was about 350 bucks. Cut your factory bell off and this thing bolts to the pump bolts. Not too tough
         
      • jas0162

        jas0162 Well-Known Member

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        I have seen adapters for the small block bell, but the one I saw had you cut off part of your block so the starter would fit
         
      • AJ/FormS

        AJ/FormS FormulaS clone 367-3.55s 3.09-1.92-1.40-1.09-.78od

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        What speeds are you thinking of cruising?
        It's a BB......roadtrip car......
        Have you given thought to just putting hiway gears in the back?
        Or maybe it already has 2.45s?These cruise at about 75=2280,and 65=1980 which is about the same as the A518 and 3.55s..
        The 2.45 rear gears likes a lower first gear, like what's in the A500 and A998/999. But 2.45s and overdrive cruises at about 75=1580,which the BB can do, but 65=1380, which it might not like,in terms of fuel mileage, especially not a 40 year old engine/carb.
        The next closest gear is a 2.76. With overdrive, that cruises 75= 1780; and 65=1540; still a bit low for the old low compression 400. Not too low that it can't do it, but too low for increasing fuel mileage.
        All rpms are zero-slip.
        There comes a point in the rpm band when lower rpm does not yield DEcreased fuel consumption. I don't know exactly where that is with a Lo-C 400.But I could guess at maybe 1800 PURE GUESS. If that were true, then to cruise 75@1800 would be, the above 2.76s and overdrive.But again at 65 you'd be out of the "zone".
        Now, if you bumped up the compression, new story.
        What hi-compression does is allow you to cruise on the top of transfers instead of on the bottom of the mains.
        The TQ carb does really well on the bottom of the mains, as does the Q-Jet, and to some extent the AFB/AVS.These are all metering-rod carbs and you can tune that part of the fuel delivery pretty lean. But Holleys and their type are not so endowed.And the low-speed circuits on them are almost invariably rich, and nearly impossible to change.After all they have a racing heritage.
        I once cruised an 11/1- 360 at 65=1590, and got phenomenally low fuel consumption with a Holley 600,leaned out specifically for the trip.
        Timing is the big thing.
        With falling rpm comes falling centrifugal timing, and falling vacuum can timing. Once you start cruising below 2000, getting adequate timing becomes very difficult, and so the engines efficiency takes a dump, and fuel-economy along with it. Timing can fall to say 18 to 20 in that range, where the engine may want 30 or 40,or more. And there is no way to give her what she wants, and still have her survive under power, short of computerized timing controls.
        Without the timing, you have to drive deeper into the throttle, and that wakes up the mains.
        The best solution is more compression. Lots more.
        But that gets you into hi-test gas on the power circuit. And since the fuel bowls are usually common to both circuits,you have to run hi-test all the time, and so now it costs more dollars per mile because of that.
        I tend to favor a minimum cruise rpm of 2000, with lots of Dynamic compression. To get 65=2000 you need 2.45s. Then crank in as much timing as she'll take. Then start leaning it out. The higher your compression ratio is, generally,the leaner you can make it.
        2.45s usually mean lo-performance on take-off, and that is why those lo-po 318s have a 2.74 low gear. This gives a starter gear of 6.71. This is about the same as the 727s 2.45 low-gear and 2.76s. So putting 2.45s behind a trans with a 2.45 is like suicide, on take-off. Thankfully your 400 brings much-needed low-rpm torque to the party.Easily enough to pull that crummy 2.45 x 2.45 starter gear. But don't try that with a slanty,lol,like I did.
        The GVOD would cost you well over $3000 installed.Probably closer to 4G.
        For about the same, you could fix your compression.And slide a lil cam in there at the same time.Not enough to affect your low-rpm performance, but enough so that when you hit passing gear, it actually makes a difference.
        I have never heard anyone say "my hi-compression engine sux".
        If you keep the 2bbl, it's probably a metering rod carb,and that's a good thing as they are adjustable. And in this case, if it's a Holly it's gonna be pretty lean already. If the car has 2.45s or will get 2.45s, then that carb is almost guaranteed to be too-lean. Unless you crank in the timing, or crank up the compression. They are adjustable.
        Happy HotRodding
         
        Last edited: Nov 16, 2017 at 5:51 AM
      • TrailBeast

        TrailBeast Slightly Twisted Member

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        If the bell was all there was to it then no, but we all know how things like this go in real life.:D
         
      • carfreak6970

        carfreak6970 Well-Known Member

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        Holy Cow guys! That is a lot more information I figured I would get from this post. Thank you!!

        it kind of stinks to hear that I cant use the BB 727 case for the A518 tail end.

        AJ brings up a good point of just changing the rear gears to get the mileage. However like you said you ruin the vehicles take off gear at that point. I was thinking of using a 3.21 gear or maybe 3.55's. However the engine would at least get a 4 barrel carb. Maybe down the road the engine would be tore into for a bump in compression and a little bit more exciting cam. But the torque curve of the engine would definitely need to be studied to find out which combo would be best.
         
      • TrailBeast

        TrailBeast Slightly Twisted Member

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        It's a small block trans, but this is one of the reasons I opted for the Dakota A500 trans.
        It bolts right up and has a lower ratio first gear than the 904 or 727.

        There are a lot of considerations when doing these kinds of swaps that a lot of people don't realize until they are into it.
        These are some general possible details.
        Flex plate to converter differences (obviously)
        Linkage changes
        Speedo cable length
        Cooler lines and fittings
        driveline length (obviously)
        Driveline angle
        Cross member mods (obviously)
        E brake cable routing
        Exhaust routing
        Possibly floor mods

        This is why I said earlier that sometimes an aftermarket OD is a better choice for some.
         
      • Bighead440

        Bighead440 Member

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        *gasp* 200-4R is what we use for clearance on retrofits. We have one behind a 392 Gen1 Hemi in a rat-rod '29 Ford with 4.11 gears and it's a highway beast!