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Thread: 4cyl to v8 swap

  1. #1

    Default 4cyl to v8 swap

    i am doing a swap/build on an 84 mustang coupe, currently a 4cyl automatic car, will be receiving a 5.0 and 5 speed. what i need to know is major differences in cross members (engine and trans) between the v8 and 4cyl variants, and if either can be re-used with the swap. ive been told i can re-use the engine cross-member just with the v8 mounts, is this correct? the trans i know will be out of an 88 gt, engine may be from same car. also, floor clearances: will i be cutting up the tunnel, or just bashing with a hammer? thanks. will have many more questions as i dive in and realize i am missing something. thanks for help and patience!

  2. #2

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    I believe the floorpans were the same by 1984 so I don't think you would need to do any bashing. I know the early floorpans had issues with this but by 1984 they were putting 5 speeds in them from the factory. The engine crossmembers are the same. Use the double-hump dual exhaust transmission crossmember from the '88 and you should be fine.

    Look at post #104 in this thread for information regarding the trans tunnel and then #109 for some pictures thereof.

    http://vb.foureyedpride.com/showthre...s-begun!/page5
    Last edited by homer302; 01-18-2017 at 02:21 PM.
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  3. #3

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    looks like the hump is more for adding the boot- wont be a big issue for me when getting it driving, may become a necessity when i start driving the car semi-regularly. thanks for the info!

  4. #4

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    Uhh, nope, that is not what it says at all. The hump is for transmission clearance because the 5 speed was larger.
    Liberty once lost is lost forever.

    John Adams
    July 7, 1775

  5. #5

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    maybe i need to read through the thread some, looked to me like cutting was needed to clear, and the hump addition was more to cover the portion of the transmission now exposed, as well as facilitate mounting of the shifter boot.

  6. #6

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    Difference in x-members, besides maybe the transmission x-member's single exhaust "hump" and maybe it's fore-aft location, are no different. V8 mounts and block brackets, yep. Years ago, I got wrecking yard mounts and block brackets from a '79 Fairmont wagon for my 4-to-8 Capri. As mentioned above, no bashing should be necessary, and if you get bashing on a sweet '84 coupe you're not going to be very popular around here, lol. If anything, the standard transmission takes up less space in the tunnel than an automatic does. A 1972 Mustang FMX transmission went into my '80 Capri, and a wee bit of sheet metal love with a ball peen hammer was only required in the area where it's kick-down bracket was.
    Last edited by Walking-Tall; 01-18-2017 at 07:37 PM.
    Mike
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  7. #7

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    the floor will not need to be bashed at all. the 5 speed will go in. the double hump cross member is for running dual exhaust. k-frame is the same 4cyl/v8. just need v8 motor mounts. no cutting will need to be done on the entire swap.

  8. #8

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    I have been building my 81 t-top coupe for a few years now. was a 4cly car. now has a 5 speed with 408 stroker. no cutting was done.

  9. #9
    FEP Senior Member
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    Automatic cars have a different hump than the 5 speed manual cars. When I converted my 86 to a stick, we had to cut the front of the shifter about an inch. Even the ashtray is different from auto to stick.

  10. #10

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    yes different hump. but the swap will work with out major cutting or bashing. minor trimming depending on the shifter being used. and it would be covered by the boot/carpet and console anyway.

  11. #11

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    If the ash tray is indeed different that is not an issue, i can simply remove it, wouldnt be using it anyways. I dont mind mild floor cutting, so clearing the shifter shouldnt be too bad if thats all ill need. with regards to the crossmember, i think ill stick with the stock i4 one for now and see if i can make it work. switching to dual exhaust is not a high priority for me, id be fine running a larger diameter single pipe out the side or rear of the car. thats assuming the only difference between the two is the exhaust humps, ive not seen the two side by side so i dont know if they are roughly the same

  12. #12
    Moderator wraithracing's Avatar
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    As stated above, the swap is basically a bolt in affair. I would recommend either buying this: https://lmr.com/item/LRS-7277A/1979-...on-Tunnel-Hump or cutting the hump out of the donor car and installing it in the coupe. This will allow you to properly use the transmission shift boot https://lmr.com/item/LRS-7277E/79-04...ith-Metal-Ring and give you better clearance around the shifter. You will need to make so cuts of the floor around the shifter for clearance otherwise it will be almost impossible to pull the shifter with the transmission in the car.

    I highly recommend the dual hump crossmember such as OEM, this: https://lmr.com/item/LRS-5059/mustan...djustable-8293 or even this http://www.buystifflers.com/1982-199...smember-2.aspx

    You can run a single large diameter exhaust, but since that is not common on most Mustangs, I doubt you will save any money compared to either using a stock dual exhaust set up or aftermarket parts. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
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    1982 GT Stalled RestoModification
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    1986 GT Under going Wide Body Conversion Currently

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  13. #13

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    Seems like everyone is making an issue out of a non issue. Installing a new floor hump is not needed at all. It can be swapped as it is. Just minor clearance as needed. The boot will also work.

  14. #14
    Moderator wraithracing's Avatar
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    Quote Originally Posted by badnightrain View Post
    Seems like everyone is making an issue out of a non issue. Installing a new floor hump is not needed at all. It can be swapped as it is. Just minor clearance as needed. The boot will also work.
    Never stated that you couldn't do the swap without the hump. I stated that I highly recommend it for street cars as it does a better job of fitting around the shifter, giving clearance and a nice flat surface for the shifter seal to seal properly on.

    I have one car that I didn't do the hump swap on and several that I did. In my experience its worth the added effort. If you experience varies, that is perfectly fine, I don't believe any of the comments above stated that it was required. Also the link provided above shows the hump being installed in my 82 GT just FYI.

    Oh one last point, the shifter boot can be made to seal on the Automatic tunnel, but again it doesn't fit properly nor seal properly without either modifying the metal trim or adding additional sealing foam, tape, etc. I just went thru this with my Road Racer as it was originally an AOD car that now has a 3550. I had to add foam tape under the sides of the metal trim to make it seal against the floor pan. Not a huge deal, but again modifications are needed. Ultimately it will get the 5 speed hump, but I couldn't put my hands on my spare one, and I got impatient.
    Last edited by wraithracing; 01-19-2017 at 12:35 PM.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  15. #15

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    Sounds like i need to add that to my to do list, once running this car will be my summer daily so i would rather spend the little bit of time and money keeping the fumes out properly. not worth suffocating to death to maybe save some time and money.

  16. #16

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    I have a 4cyl standard that I am trying to convert to an automatic. I, too, am having difficulty determining what modifications need to be made for everything to fit properly while maintaining a stock look.

  17. #17
    FEP Super Member xctasy's Avatar
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    Ultimately, Vee-Eighting IT is simple with Fords, but not quite as simple as it is with brand G or M or C.

    With Fords, its kinda like Subway, except sometimes you can't have the topping just the place you like it because it won't go with the basic burge bun. Its like Cheif Ramsey comes out Psycho and tells you your being difficult, no one puts stuff like that on a Burger, for G""d sakes.

    With Fords, the basic burger bun is customised a little, and different kinds of Vee Eight spice gets put in.

    transmission humps,
    axles,
    and crossmember differs a little.

    The 5.0/AOD topping will always fit, but you might have to do a little bit of repostioning the anchovies.


    But you can put anything with anything if you find out what has to be shifted or changed.


    Induction and gearing cause a little bit of strife.

    With AOD's and the engines induction system, it gets a little more tricky becasue until 1986, the Automatics and Stick shift v8's had entirely different shift rods and actuators to and from the engine to trans. The whole induction system, including the intake manifold, varied to kow tow with the transmission

    From 1979 to 1985, if it was an Auto, the V8 stuff was raided from other luxuary Lincolns, LTD/ Crown Vic/ Gran Marq (Panthers).

    If it was a 1979 or 1982-85 V8 Manual, the carbs got raided from the F series Trucks, the gearboxes from the fat old 70's square rigger Granadas, Datsun 280ZX-Turbos and AMC inventory.Litterally slapped together with love on the production line with Hot, stolen inventoy gearboxes.

    There was a high degree of customisation in order to use truck or luxuary car parts. If it was a soft spec 5.0 or 4.2 auto, it used freely availalbe big car parts. If it was a performance 5.0, it used truck spec parts, but not everywhere.

    So when you put in a V8 where an I4 was, you've got to be particular about what gearbox/transmission/axle combination, as well as what kind of induction (carb/throttle body injection/port injection) combination you have to use.

    So if you want, say, a B&M Hammer shifted AOD in your 5.0, you'll have to decide what carb/throttle body or EFI your going to use.


    Words like C3/C4/C5 or C6 or 4W70 are used for Ford automatics, its not just AOD's, and they go together with different parts to make it "hitch"

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