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Rear-engine Conversion Kit

A conversion kit to move a front-wheel-drive car's engine and transmission to the back
  (+4, -1)
(+4, -1)
  [vote for,

I keep coming back to this problem. The current prevalence of front-wheel-drive cars means that most cars have a fairly low limit to performance tuning, whereafter traction under acceleration becomes problematic.

One solution is to move the engine and gearbox to the back of the car, thus producing a mid-engined layout, as the drive on front-drive cars is usually taken from the hinder part of the engine/gearbox assembly. However, in order to retain use of the rear seat and instead forego the hatched load space (some load area becoming available in the now-vacant engine compartment), I propose a kit that flips the gearbox upside-down to produce a true rear-engined layout, with the engine and gearbox behind the rear-wheel centreline. Flipping the gearbox has the advantage that all the gearchange linkages etc. remain pointed in the general direction of the driver, and are therefore easier to adapt.

Wary of savage oversteer, I was reluctant to consider this, until I did some math and found that doing this to my Mk1 Golf would change the weight distribution from 64/36% to around 48/52%, which is hardly suicidal. In fact it is ideal for many forms of spirited motoring.

Later recalculation: the figure of 120kg was based on information for an early EA827 1500, less starter and clutch, and is therefore a bit light. Recalculating for a more realistic 160kg gives 43/57%: hairier but still not exactly lethal. The iron EA827 is heavy for an econobox engine: this done to something with an aluminium engine might deliver less rear bias.

In addition to a bolt-in subframe, the kit will include the requisite engine-to-gearbox adaptor plate; a firewall/engine cover/partition; cutting templates; all the necessary pipes, hoses, linkages, and sundries like brake proportioning valves; and a DeDion axle that runs across the front of the engine/gearbox assembly, located and sprung off the subframe. A DeDion axle has the right camber characteristics for drag racing, and a narrow-track version could be optional for large-rubber applications.

Engine access would be if anything better than stock, especially if the subframe is so designed as to allow a lot of the rear sheetmetal to be cut away if one should desire to do so. The resulting look has some considerable appeal: a bit of rake, roof-top scoop, wheelie-bars emerging from amidst divers mechanical gubbins under the taillights. Nasty.

Ned_Ludd, Nov 20 2007

Renault 5 Turbo 2 http://www.clubalpi...lassifieds_sale.asp
Factory version of idea using LeCar instead of Golf [MisterQED, Nov 20 2007]

Pontiac Fiero http://en.wikipedia.../wiki/Pontiac_Fiero
not obvious from wiki but this is exactly it: FWD setup dropped in the rear [AutoMcDonough, Jun 16 2011]

Smyth Performance g3f build blog http://g3f-jlphil.blogspot.com/
Guy named Phil building the beta version of the Smyth Performance G3F, which takes a Jetta and turns it into a mid-engine 2-seater sports car. [cajunfj40, Mar 29 2012]


       I'm not sure how you arrived at your weight distribution, I reckon a Mk1 Golf weighs about 800Kg. Of that, about 200Kg is the engine and transmission. removing 200Kg from the front axle and adding it (and more for the subframe) to the rear would change the 64/36 distribution to a lethal 39/61! Far from cutting away sheet metal at the rear, you would probably need to add more than you remove to give the sfiffness required to support the extra power.   

Twizz, Nov 20 2007

       Or you could turn all the seats around and drive in reverse.
hippo, Nov 20 2007

       I was working on 840kg and 120kg, respectively, and factoring in the leverage derived from the fact that the engine is a short distance ahead of the front wheels, and would now be a short distance behind the rear wheels. I did not consider the effect of moving the spare wheel to the front, though.   

       Keep in mind that a lot of heavyish stuff stays at the front, like the battery and radiator, whose effect is multiplied by the polarity of its location.   

       Indeed, all this will increase polar moment of inertia somewhat, which has advantages and disadvantages.   

       The idea was that the result of the subframe would be structurally to replace sheetmetal with tubing: but as regards stiffness, any sort of rearward weight bias argues for very little roll stiffness at the back. If any additional structural stiffness is required it is therefore likely to be distributed along the entire wheelbase (think roll cage) with no consequent effect on weight distribution.
Ned_Ludd, Nov 20 2007

       Have you ever heard of a fiero, or a toyota MR2? Do some research and it will dispell your mistaken assumption that maintenance will somehow be improved.   

       I would also take issue with the assertion that FWD cars do not perform well. In general I suspect this has far more to do with the fact that in general a FWD design is primarily used for budget automobiles due to the great savings from manufacturing. The situations in which a FWD car is actually at a disadvantage to a RWD car are limited and there are a number of situations in which a FWD car would in fact excel over its RWD counterpart. In reality the best avenue is to pick the configuration that best meets the needs of the driver in a particular situation.
jhomrighaus, Nov 20 2007

       I used to have a Porsche 924S - beautiful thing, front engine, rear-drive, with the transmission (gearbox to us Brits) sitting above the wheels at the back - giving it near perfect 50/50 distribution; it was the best poised car I've ever had the joy of driving. Quite lovely.   

       I'd get another one, but I live in London now, and with all the traffic, it would be like keeping a horse in a windowbox.
zen_tom, Nov 20 2007

       [jhom], note the word "however" in the second paragraph, and the sentence that follows it. I have heard not only of the Fiero and MR2, but also of the MGF and Boxster, whose engines are reached by threading coat hangers through grommet holes.   

       Note also the second sentence of the first paragraph. I am indeed talking about the needs of a driver in a particular situation, a very particular situation. To your probable next question, i.e. why I don't start with a rear-driven platform, the answer is that I like messing with stuff, which I'm sure you'll understand.
Ned_Ludd, Nov 20 2007

       I suppose I understand. That must be why there is a 65 MG Midget in my garage having a 2.5 Liter engine out of an s10 pickup being transplanted into it.
jhomrighaus, Nov 20 2007

       Well you can't argue with better weight distribution, but a LSD can sometimes make a FWD car on par with a RWD. I know some cars that have longitudinally mounted engines yet are FWD (old Acura RL), and while I don't know any that are transverse and RWD, there are some that are AWD (Mitsubishi Lancer EVO, new Acura RL). Perhaps it would be neat trying to send the power to the rear without changing the engine layout.   

       But I still do like the idea for this kit [+].
acurafan07, Nov 20 2007

       Certian GM cars and Chrysler Minivans have a FWD transverse layout with an AWD add on.
jhomrighaus, Nov 20 2007

       It's been done, but it is FAR from a kit. I personnally liked when they left the motor in the front of the golf and put one in the back for a crazy 300+HP four wheel drive hill climbing Golf. Cutting out that much metal from a unibody car could never be a kit unless you partially converted it into a body over frame car which is how it's done everytime I have seen it. The other issue is noise, smell and danger as placing a motor into the passenger compartment requires a firewall, etc. I think the weight distribution issues are workable. You will be moving the 10 gallon gas tank up front which is 60lbs+ wet weight. For reference look at the Renault 5 Turbo 2 (link) which is a factory version of the idea, though they did it with a LeCar instead of a Golf. I saw one of these at a car show and fell in love.
MisterQED, Nov 20 2007

       I think your best bet if you want a cheap rear engine car for racing is to buy an old VW Bug or Chevrolet Corvair and add some aftermarket performance parts. I think you'll find flipping the gearbox would be near impossible, and you might find it easier (if you have a single cam engine) to just make the engine run backwards.
discontinuuity, Nov 20 2007

       Cool, four wheel steering!   

       Why would anyone at the halfbakery want to do something the easy way? Why not just do it the hard way and keep the engine facing the same direction. Maybe you could make it have some kind of electronic gear selector.
BJS, Nov 20 2007

       [rasp], old Bugs are getting a bit thin on the ground, most either having had some form of understandable liberties taken or having been surfered or studented to near-death; and as for Corvairs, they're rare and exotic in my part of the world, and those who have them think they are sitting on goldmines. But I'm not specifically looking for a rear-engined car. I'm looking for a way to extend the tuning viability of available cheap hatchbacks.   

       I disagree about the impossibility of flipping gearboxes. Many earlier conversions used inverted gearboxes, especially those that used VW, Imp, Fiat, or Renault 'boxes in mid-engine applications. Then there are those stock-car Muncies and Toploaders lying on their sides. A conventional manual 'box's oil isn't circulated, it just sloshes around. That it doesn't much matter which bit is in oil and which isn't, as long as the oil/air proportion is within limits, is evinced by my Golf's synchros sitting on different shafts. Two are deep in oil and three shallow: flipping the 'box would just put three in deep oil and two in shallow. But, yes, flipping an automatic would be near impossible.   

       [jhom], yes, I like the idea of an AWD add-on. I've speculated on that idea: perhaps I shall revive it. I'd done searches for what's out there and found very little by way of technical nitty-gritty. Do you perhaps have a link or two?
Ned_Ludd, Nov 21 2007

       So are you turning the gearbox 180 degrees about its vertical or horizontal axis? How are you going to link it up to the engine again?
discontinuuity, Nov 21 2007

       I'm flipping it about the clutch axis. It'll be bolted up to the engine via an adapter plate, and all the usual ways of dealing with the extra length. So, the engine is in the same orientation as before, only the crank CL is about 8" behind the final drive CL, not 8" ahead of it.   

       I've looked: the water pump will have to be relocated, in the case of a Golf 1. I see this principle being applied to different cars, that will therefore throw up different little problems like that.
Ned_Ludd, Nov 21 2007

       While I like this idea, I used to have a MkI and the forward distribution of weight combined with FWD made for excellent snow driving in subarctic regions. Moving the weight backwards would be as bad as moving the engine backwards, if for instance you need to stop at a stoplight, facing up hill, on ice.   

       The only way to improve that would be to power the rear wheels. But I personally like the handling of a car that can fishtail easily (or do they call that something else these days?). If I could move the driver's seat on top of the engine I'd be even happier. Who needs the rest of the car anyways?
mylodon, Nov 21 2007

       i can see what you are wanting to do. you can get a good result in several ways. you can do a ditrect transplant of a front wheel drive engine and transaxle to the rear of the car. basically what was done with the fiero. or you can get a transaxle out of a mid engine car and mount it in the rear and leave the engine in the front, just moved back to the firewall some and connect the engine and transaxle with a tube and a driveshaft inside it. the free space in front of the engine frees up room to add oil coolers for the transaxle and engine. also frees up room for a second battery. in the end it is well balanced and handles great and little effort to build.   

       how do i know this, i love building hot rods for people and keeping them different. it is amazing what you can build from a salvage yard and reading what the big name builders are doing. follow your building dreams.
TAGAutoSports, Mar 28 2012

       <see linky> Baked, well sorta. There is a kit to make a FWD Jetta into a Mid-Engine 2-seater sports car. Smyth Performance G3F ~$10,000 "kit car" that uses a late model Jetta as a donor. TDI preferred. Uses the subframe, firewall, lower front half of passenger area (cut off behind rear doorjamb and about level with top of doors) and trunk lid/attachment. Bolt in spaceframe, new front and rear body panels and roof/windshield/doortops. Moves engine to behind front seats. Keeps factory Jetta interior/airbags/etc.
cajunfj40, Mar 29 2012


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