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Thread: Front to rear engine conversion question

  1. #1
    Senior Member dman1409's Avatar
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    Front to rear engine conversion question

    Hi guys, im planing on moving my engine (peugeot 406 coupe) to the rear after welding in a frame.

    my questions:

    - What are the key measuring points i have to use for setting the correct hight / distance from front weels?

    - Are there any useful trics for determining the correct engine position and position of the mounts?

    - are there any standard rules for engine placement?

    cheers!

  2. #2
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    Quote Originally Posted by dman1409 View Post
    - What are the key measuring points i have to use for setting the correct hight / distance from front weels?
    - Are there any useful trics for determining the correct engine position and position of the mounts?
    - are there any standard rules for engine placement?
    There's a lot to consider when moving a front wheel drive cradle to the rear of a car. The engineers at Pontiac did just that when they built the Fiero… they took the front end of a Chey Citation, made a few modifications to it, and simply slid it backwards and designed the Fiero chassis around it. Even with the benefit of a chassis designed to take the engine cradle, they still got a number of things wrong. You're starting from a point much worse off.

    1. before anything else, get digital drawings of the chassis, engine sub-frame, engine, transmission, and suspension... if you can. You'll need these to know whether the engine/transmission assembly will be able to fit in the space you have, without cutting up your chassis only to find it doesn't;

    2. next you have to locate the engine/transmission assembly in the chassis front to rear, and up and down so that the output shafts of the transmission align with the axle centerlines of your hubs, and so that the hub centers align with the wheelhouse (fender opening). Modern CV joints can operate at an absolute maximum of about 26 degrees misalignment if you have to move things around to accommodate the space you have available, though 10 degrees is far more forgiving;

    3. next locate the engine and transmission side to side in the space you have to center the assembly as best as possible for weight distribution and to clear any frame components;

    4. once you done that, you'll be able to design a subframe that supports the engine/transmission at their OEM mounting points, and which connects the sub frame to the chassis, but it's unlikely you'll find anywhere on the rear chassis that's going to be strong enough to mount your new subframe to since it wasn't designed with a rear engine in mind;

    5. it's best to stick with OEM mounts and mounting locations on the engine/transmission since supporting this weight and damping vibrations is a whole other science;

    6. assuming you're planning on using the suspension from the front end of the car at the rear end, you'll need to design new strut mounts in the rear, and find a way to connect the steering tie rods to a fixed point on the chassis to prevent them from steering. If you get the mounting point wrong on the strut mounts, or on the tie rods, you'll get poor camber change resulting in poor handling, and/or poor dynamic toe change resulting in bump-steer. Both of these were problems on the Fiero; If you plan on using the front control arms on the rear, you'll also have to angle them differently than they were in the front in order to achieve anti-squat since otherwise they'll give you pro-squat. It's possible to design around these problems but it takes a really good understanding of suspension design, otherwise it's a crap-shoot with a far greater risk that you'll get it wrong than right.

    7. you'll also need to redesign the front suspension, an exhaust system, consider what you've done to brake bias, reroute the fuel lines, coolant lines, cabin heater and a/c lines, battery cables, throttle cable, transmission cables, and most of the wiring harness. Then you'll need different sway bars, relocate the gas tank, spare tire, and probably design a whole bunch of other smaller stuff like wheel well liners, brake lines, engine air intake & filter, accessibility of oil fill port, spark plugs, and on, and on.

    I don't know you at all, but the bottom line is that it will take a lot of ingenuity, fabrication skills, time, money, and space to accomplish this. If you're planning on going through this much work, you should honestly consider an engine upgrade as well. Keep us posted on your progress if you decide to carry through with your plan. Good luck!

  3. #3
    Senior Member dman1409's Avatar
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    Hey Blooz, Many many thanx for your detailed explaination!!! I really apreciate that! cheers!

  4. #4
    That is a pretty good analysis. One thing I might add and may not be an option for what you are trying to do. To make the swap a tiny bit more simple, do this to a car with an AWD/4WD option or a similar sized car and use that rear suspension. That way your hubs already have splines for the axles and you can use the existing rear suspension to remove all of the work needed to make the front suspension work, you would potentially just need custom length axles at that point.

  5. #5
    Senior Member Dangerrous's Avatar
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    take a look at JD's build on the extreme site, he's already done it

  6. #6
    Senior Member dman1409's Avatar
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    Quote Originally Posted by Dangerrous View Post
    take a look at JD's build on the extreme site, he's already done it
    I carefully studied it indeed... i even went to durham.. haha so i have a prety good idea of the framework but did not knew the rules of thumb for locating the engine... so i'm well happy happy with this aditional information...

    the bummer is Brexit... i need MOT in uk for my car... can get it street legal here except if it is legalised in a EU country.. so need to get her built and inspected before march 30th 2019

    thats a massive challenge...

  7. #7
    Senior Member dman1409's Avatar
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    Quote Originally Posted by drxlcarfreak View Post
    That is a pretty good analysis. One thing I might add and may not be an option for what you are trying to do. To make the swap a tiny bit more simple, do this to a car with an AWD/4WD option or a similar sized car and use that rear suspension. That way your hubs already have splines for the axles and you can use the existing rear suspension to remove all of the work needed to make the front suspension work, you would potentially just need custom length axles at that point.
    Thanx for you comment but as u mentioned thats not really an option as the pug is the best donor

  8. #8
    Senior Member ITALIANKNIGHTRIDER's Avatar
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    post a link to JD's build on the extreme site
    In the USA if you pay a company / person to start a plug, then it,s your plug and work ,it is not theirs to sell or trade !!

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