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Thread: Big Block Swap Questions

  1. #1

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    Big Block Swap Questions

    Will a Mopar RB series engine fit into our little trucks without the modification being too severe? I want to put some big V8 power in my truck, but I don't want to have to modify the frame. Will it work if I fabricate some new engine mounts and find a tranny that will fit as well? Or is there significant work that needs to be done by a professional? Any and all help is much appreciated.

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    I think the Mopars fit real well as far as I know. The guys with V8's are probably still asleep, but they will stop in sometime. There's easily 6-8 guys that stop in pretty regular. Meanwhile check out some of the build threads of the swaps.

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    V-8 swap was easy, just needed to fab up some engine mounts and make a new tranny X-member. You "might" need to do a little cutting to the tranny opening on the fire wall (not sure with the Dodge tranny bell housing). You will need to relocate the rad either under the header panel or in front of it. Scavenge some exhaust manifolds that will clear the steering and frame,and have the front of the drive shaft shortened with a Dodge(ford,Chevy) yoke welded on.

    Took me about 3 weeks to do my swap and get everything working right.

  4. #4

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    xmember doesn't need to be changed if you mount a 318 or 360 to a small block 727 or 904. The 727 will require firewall and floor mods. The 904 will fit without mods, bolt up, use the OE speedo cable and everything. It's just a harder trans to find a V8 version of since it was used on smaller engines. I'd love to put a 5.7 hemi in one with a 727 with O/D. The 5.7 is a small block. You can buy a carb intake from dodge and run a MSD box to fire both plugs per cylinder at one time. That engine puts out about as much as big blocks with less weight. It just needs rod and springs replaced with stronger ones before you put it in the truck. That'll be pushing 350hp in a 3000 lb truck (fully loaded with a/c, p/s and full tank of gas + me) and that's more than enough power for these. If you could find a way to keep and control VCM under these conditions you could probably get wicked HWY MPG. Don't forget the 5.7 block can go up to a 6.4 but you'll pay for those engines. May as well bore and stroke the 5.7 and you've got the same engine as the 392 or 6.4

  5. #5

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    Glad to hear and thanks for all the help. The big blocks are a lot easier to find and less expensive in my area so that's why I was looking at them instead of the small block. What kind of transmission fits well with that if I want to keep my truck a manual instead of switching to an automatic? If I can find a small block for a decent price I'd go wit hthat just to make life easier, but with what I've found so far it looks like I'm going big block.

    Fordubishi- How much work were you doing on the swap daily for the three weeks? Was it three weeks of nothing but working on the truck or three weeks of a couple hours in the evening and weekends?

  6. #6



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    Fordubishi is in flood conditions near home. Traded his truck for a rubber raft and ducky until the flood waters subside. He stops in regularly.

  7. #7


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    about 3 weeks working 3-4 hrs a night and 6-7 on the weekends. that also includes running to the junk yard looking for parts.

  8. #8

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    The 440 will fit, the radiator has to be relocated in front of the core support though. You'll need an aftermarket radiator though, or the radiator for an A-Body (HD/AC cooling package) or one for a B/C/E Body. I have a HD C Body Radiator in my D50 and it sits between (tight against) the headlights.

    The transmission tunnel needs to be reworked/modified near the firewall, the SB 727 barely fits after working the tunnel entrance over, the BB is even bigger. You can use a BB 727 or an A833 4-Speed, the NP435/445/540 truck transmissions won't work, the shifter is too far forward (would actually be inside the dash). You could also use a 904 or an A518 Overdrive if you cut the bellhousing off and install an Ultrabell.

    I had a 4x4 MA904/TF904 hybrid transmission in my D50 for a couple years before I replaced it with a 727. I was getting 19mpg out of her with a heavy right foot, 33" tires and an engine from an old drag car. Now it sits on 40" tires and I'm afraid to see what mileage it gets

  9. #9

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    Does anyone know if a Keisler transmission will work? Their transmissions are designed for cars so I shouldn't run into the issue with truck transmissions with the shifter coming through the dash, but I'd have to go to a divorced transfer case. Any thoughts?

  10. #10

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    If you're going to keep it a 4x4, the 727 is your easiest approach for a transmission. There's also a 4WD version of the Chrysler A833-OD 4-Speed that was sold to chevy for use in their 80's trucks, if you want a 4-Speed and 4WD. Since the A833 and A833-OD (the A833-OD is an Overdrive version that was introduced in the early 70's) use a linkage driven shifter, you can relocate the shifter anywhere you want.

    Expect to encounter some space issues with the conversion/swap (No worse than a Hemi in an A-Body, actually the Hemi in the A-Body is a little worse, the valve covers on that pretty much touch the fenderwells even after modifications on that swap). It wouldn't hurt to ditch the Power Brake Booster and use a "Hemi A-Body" Offset Master Cylinder adapter to move the master cylinder away from the engine a little

    Here's an LA series Small Block Mopar in my '84. The B/RB series big blocks don't take up much more space, they're only a little wider, a little taller and a little longer...they're a lot heavier though. A fully dressed (complete, with accessories) LA is about 540 pounds (roughly 500 if you swap to an Aluminum Intake), A fully dressed B/RB is roughly 720 pounds. Add an Aluminum Top End (heads and intake) to either one and you can knock 100+ pounds off the engine. Either way, it's going to be fairly nose heavy and with the stock IFS suspension, it's going to want to nose dive like crazy...comparable to dropping a Big Block in an A-Body. Those things are nose heavy and want to plow through turns, but man are they fun.

    The usual Muscle Car tricks apply to this situation if you want it to be a little more friendly. Relocate the Battery (under the bed, like a factory 4D55 Diesel truck), ditch the A/C (if equipped), convert to Fast Rate Manual Steering, go with an Aftermarket Aluminum Radiator, use Aluminum Bumper Brackets, etc to remove and shift weight further back.














    Even after beating the crap out of the transmission tunnel entrance, it still took me 10+ hours to wrestle the SB-727 up into the truck. And I had to cut away the side of the tunnel and part of the floor (fabricated a removable panel) to access the shift & kickdown levers. The V8 Swap was the best thing I ever did to the truck though, man did it light a serious fire under its butt
    Last edited by 74Dusted; 06-25-2013 at 02:37 AM.

  11. #11

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    Good looking truck, I am kinda set on the big block just because of price and availability where I'm at. I really want a 5-speed manual, but from what I've found the only ones that bolt up to the big block are the Keisler transmissions that I mentioned before, Do you think it would work to fit a car tranny and t-case under the truck to still have the 4wd or would there be a major fitment issue?

  12. #12

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    You'll still have to modify the tunnel to make either a 727 auto or a M/T work. The mopar m/t's used that mess of brackets on the side of the trans for the shfiter but you may be able to cut out the floor and weld in a hump like they did in the older cars. Their floors were extended for the shift brackets. If you're going 4x4 anyway do a 3" body lift. That should solve alot of the space issues with the tunnel.

  13. #13

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    I was just thinking about it and was wondering how much power the stock diff can handle. Will it hold with over 400 lb/ft of torque or will I need to swap it out for a beefier one? Thanks

  14. #14

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    I have one with a stroker 340 in it and I have a 9 in. ford rear in it. My trans tunnel is cut out and a fabricated one in it.Click image for larger version. 

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  15. #15


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    So what's run.

  16. #16

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    Best so far is 6.34,1.34 60ft. @ 108 mph in the 1/8 mile.

  17. #17

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    I've been thinking about it and I think when I do the swap I'll put a Dana 60 in the rear. Stronger than the Ford 9" only downsides are that it's a bit heavier and I would have less options for gear ratios, but I'm not too concerned with either of those.

  18. #18



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    use an 8 3/4 rear from an a body mopar - its the right width and the spring perches even line up with the leaf springs - plenty of gears and lockers.
    Pennyman1
    The best Dodge that Dodge never made
    Living the D-50 lifestyle since 1980

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