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Discussion Starter · #1 ·
I started the initial enquiries about doing this back in summer 2019 but, by the time I started getting my facts together, covid arrived, work went crazy and it just went to the back of the to do list.
However, I’ve spent a little bit of time pondering it again recently as I do want to start moving forward with it.

my original plan was to source a decent DC motor but, they do not seem to be as plentiful here in the UK as elsewhere in the world so that ended that idea.

I then started looking at conversion kit - netgain and they seemed expensive for what I wanted to do?

However, due to the extra couple of years I’ve been dragging my heels, the price of used EV motors seem to have become far more reasonable and it seems the obvious route to go down. The same appears to apply to batter packs, etc.

At this point, my main stumbling block seems to be the fact that I want to drive the vehicle through the rear axle via the torque tube fitted as standard but, identifying a motor that isn’t a dual drive seems to be an issue.

I know the obvious answer would be to convert the rear axle from an EV but, it doesn’t seem that simple as essentially, the rules in the UK would make it problematic and the vehicle would potentially needed to be inspected as it had been ‘significantly altered’ and there’s no guarantee it would pass - and I’d have a vehicle I couldn’t drive!

An engine/drive conversion is far easier to get sorted so, ideally, I need to utilise the torque tube?

Im not that bothered about turning the car into a beast, it only had 120bhp when new so if I would up with a similar amount of power - say from the 88kw Nissan Leaf, I’d be more than happy and wouldn’t need to worry too much about uprating the brakes etc.

Any suggestions or direction gratefully received!!
 

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At this point, my main stumbling block seems to be the fact that I want to drive the vehicle through the rear axle via the torque tube fitted as standard but, identifying a motor that isn’t a dual drive seems to be an issue.
What do you mean by "dual drive"? Do you mean that all you are finding are drive units which include the motor, reduction gearbox, and differential, so that there are two output for axles? You don't want the reduction gearbox from that anyway, so the two axle outputs are not the only issue.

I know the obvious answer would be to convert the rear axle from an EV but, it doesn’t seem that simple as essentially, the rules in the UK would make it problematic and the vehicle would potentially needed to be inspected as it had been ‘significantly altered’ and there’s no guarantee it would pass - and I’d have a vehicle I couldn’t drive!
That would be converting to a complete drive unit, rather than "rear axle". Other people from the UK and other European countries have mentioned this regulatory issue.

An engine/drive conversion is far easier to get sorted so, ideally, I need to utilise the torque tube?
If you keep the original transaxle, the motor will likely only fit where the engine was. So you need the shaft which is inside the tube, and something has to handle the torque reaction to driving the shaft, which in the 924 is this tube.

Most motors will be too large to fit anywhere but where the engine was, but if you could mount the motor further back then you could use a shorter version of the torque tube. Maybe the torque tube could be cut off immediately ahead of the rear suspension torsion bar housing, and the motor installed behind the front seats, immediately ahead of the torsion bar housing? It looks like there might be room...
Wheel Tire Car Land vehicle Vehicle


Im not that bothered about turning the car into a beast, it only had 120bhp when new so if I would up with a similar amount of power - say from the 88kw Nissan Leaf, I’d be more than happy and wouldn’t need to worry too much about uprating the brakes etc.
As far as I have seen, the versions of the Leaf have been rated at 80 kW, 110 kW, and 160 kW (not 88 kW)... but that does make sense.
 

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Discussion Starter · #4 ·
What is "the vehicle"?
A Porsche 924 2.0 model with a dead engine.
What transmission is in it?

What's redline on the ICE?
What do you mean by "dual drive"? Do you mean that all you are finding are drive units which include the motor, reduction gearbox, and differential, so that there are two output for axles? You don't want the reduction gearbox from that anyway, so the two axle outputs are not the only issue.


That would be converting to a complete drive unit, rather than "rear axle". Other people from the UK and other European countries have mentioned this regulatory issue.


If you keep the original transaxle, the motor will likely only fit where the engine was. So you need the shaft which is inside the tube, and something has to handle the torque reaction to driving the shaft, which in the 924 is this tube.

Most motors will be too large to fit anywhere but where the engine was, but if you could mount the motor further back then you could use a shorter version of the torque tube. Maybe the torque tube could be cut off immediately ahead of the rear suspension torsion bar housing, and the motor installed behind the front seats, immediately ahead of the torsion bar housing? It looks like there might be room...
View attachment 128504


As far as I have seen, the versions of the Leaf have been rated at 80 kW, 110 kW, and 160 kW (not 88 kW)... but that does make sense.
By dual drive, I’m probably using the wrong terminology but, I refer to the two drive shaft outputs but, obviously, I only need one to connect to the torque tube - or be adapted to connect to the torque tube.
From my desire to keep the conversion ‘simple’ and avoid the regulation nightmare, the electric motor will have to be placed in the engine bay.
 

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By dual drive, I’m probably using the wrong terminology but, I refer to the two drive shaft outputs but, obviously, I only need one to connect to the torque tube - or be adapted to connect to the torque tube.
The problem is that if those two outputs are for the axle shafts, they are driven through a lot of reduction gearing - an overall reduction ratio from motor speed to axle speed of about 7:1 to 12:1 for typical EVs. Feed one of those to the transaxle of the 924, and even in top gear the transaxle will multiply that by a further 3:1 or so (depending on transaxle model and ring-and-pinion ratio), resulting in a car that spins the motor to its top speed at a road speed appropriate for a city street - not a highway.

In earlier threads it looked like the plan was to use a 1986 924 S, but that would have a 2.5 L engine rather than a 2.0... so just as an example, the 1986 924 S would have a 5-speed transaxle (assuming it's manual) with a 0.857 fifth gear, 3.889:1 final drive, and thus 3.33:1 overall reduction gearing. Multiply that by the 8.193:1 gearing in a Leaf transaxle, and you have about 27:1 overall, so with the Leaf motor at 10,500 RPM the wheels would only turn 385 RPM, or with the stock 195/65R15 tires (830 revolutions per mile) a road speed of 0.464 miles per minute or 28 MPH.

You can use the transaxle that comes with a motor salvaged from a production EV (and deal with regulatory issues), or the transaxle that came with the car, but not both unless at least one of them is significantly modified.
 

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Discussion Starter · #8 ·
Bolt the motor to the transaxle, ditch the tube
What motor is suitable?
The problem is that if those two outputs are for the axle shafts, they are driven through a lot of reduction gearing - an overall reduction ratio from motor speed to axle speed of about 7:1 to 12:1 for typical EVs. Feed one of those to the transaxle of the 924, and even in top gear the transaxle will multiply that by a further 3:1 or so (depending on transaxle model and ring-and-pinion ratio), resulting in a car that spins the motor to its top speed at a road speed appropriate for a city street - not a highway.

In earlier threads it looked like the plan was to use a 1986 924 S, but that would have a 2.5 L engine rather than a 2.0... so just as an example, the 1986 924 S would have a 5-speed transaxle (assuming it's manual) with a 0.857 fifth gear, 3.889:1 final drive, and thus 3.33:1 overall reduction gearing. Multiply that by the 8.193:1 gearing in a Leaf transaxle, and you have about 27:1 overall, so with the Leaf motor at 10,500 RPM the wheels would only turn 385 RPM, or with the stock 195/65R15 tires (830 revolutions per mile) a road speed of 0.464 miles per minute or 28 MPH.

You can use the transaxle that comes with a motor salvaged from a production EV (and deal with regulatory issues), or the transaxle that came with the car, but not both unless at least one of them is significantly modified.
Ok. I’ve had a good crawl under the car and although it’s a guesstimate at this time, it looks like if I removed the gearbox and the fuel tank which lives above it, depending on the overall dimensions of the donor motor, I could mount it in place of the gearbox and then just have to overcome the issue of the driveshafts but, I’m guessing that there are specialists out the who can sort the issue of the driveshafts out?

If I could achieve this, it would still mean the car was RWD and although I have no idea of the weight of a suitable EV motor, I’m guessing the it wouldn’t be more than the weight of the gearbox, a full fuel tank and a percentage of the weight of the torque tube. This would mean I could have the whole of the engine bay to use for batteries etc and hopefully keep some of the well balanced characteristics of the 924?
Am I heading in the right direction?

Re using the 2.0 over the ‘S’, the rationale is that the 2.0 car I have is a nice tidy car and ready for the road as soon as a conversion was done as opposed to the donor S which would then require a lot more work, including paint, after the conversion was completed.
 

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A Leaf motor (not drive unit) adapted to the transaxles seems simplest - no axle mods, and the 110kW/160kW get you a nice conservative boost in performance. You'll need to stuff a battery pack and the inverter/dcdc ("PDU") into the car, the former where the engine was and maybe down the torque tube tunnel.

You can use other motors as well and some may have adapters already made for that transaxle - I don't know what's out there.
 

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Ok. I’ve had a good crawl under the car and although it’s a guesstimate at this time, it looks like if I removed the gearbox and the fuel tank which lives above it, depending on the overall dimensions of the donor motor, I could mount it in place of the gearbox and then just have to overcome the issue of the driveshafts but, I’m guessing that there are specialists out the who can sort the issue of the driveshafts out?
I assume that you're talking about a complete drive unit here - the motor and transaxle that comes with it, not just a motor.

I don't know who can be trusted to sort out the axle shafts, but if you understand what you need there are certainly businesses which can build the required shafts.

If I could achieve this, it would still mean the car was RWD and although I have no idea of the weight of a suitable EV motor, I’m guessing the it wouldn’t be more than the weight of the gearbox, a full fuel tank and a percentage of the weight of the torque tube. This would mean I could have the whole of the engine bay to use for batteries etc and hopefully keep some of the well balanced characteristics of the 924?
Am I heading in the right direction?
A complete drive unit will be heavier than the transaxle, but not unreasonable for the car (given the removal of the fuel tank and muffler). This seems like a reasonable approach to me, provided that you can overcome any regulatory issues from replacing the transaxle, and if the drive unit fits with the car's rear suspension.
 

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Discussion Starter · #11 ·
I assume that you're talking about a complete drive unit here - the motor and transaxle that comes with it, not just a motor.

I don't know who can be trusted to sort out the axle shafts, but if you understand what you need there are certainly businesses which can build the required shafts.


A complete drive unit will be heavier than the transaxle, but not unreasonable for the car (given the removal of the fuel tank and muffler). This seems like a reasonable approach to me, provided that you can overcome any regulatory issues from replacing the transaxle, and if the drive unit fits with the car's rear suspension.
I’ve had quick look on eBay and if I’ve got my head around this - there is a lot to take in when you’ve never done it before - this is what I need, the complete unit - all I need to do is work out how to introduce it into the rear, mount it correctly and then overcome the driveshaft issues?

Automotive tire Motor vehicle Vehicle Automotive exterior Rim
 

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Well, kinda. It is a starting point. Goes downhill from there fast because unless someone did it before you, there bunches of the pesky hunh? moments still to come. That's why you feel so proud being finished. Remember, 90% of homebuilder airplanes never get to fly
 

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Discussion Starter · #14 ·
After a bit of digging, it appears the mai problem I’m likely to come up against here in the UK is the registration post conversion and whether the work would be accepted or, whether it would have to go through specialist approval which could make it very expensive and, no guarantee that it would pass.
I light of this, I’ve made an appointment to speak to one of the vehicle examiners who undertakes these checks to get some facts before I start doing anything!

from the reading I’ve done - disappearing down many rabbit holes - it make sense, if possible to mount at the rear, placing It essentially where the gearbox is now but, I think it’s classed as a significant structural alteration which is where the issues lie!
Let’s see what next week brings!
 

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In my opinion keep the complexity down. Obtain the Nissan motor and inverter. Remove gearbox from Nissan motor. Get a coupler made to fit between Nissan motor and original gearbox if its a manual. Get one of the available control boards to control the Nissan inverter. Then you can work on the rest of the car without the additional stress of redoing the entire driveline. On my RWD project I have a AC motor spinning the driveshaft via the original gearbox and its all been quite complex enough for me. Thats my 2 cents. Converting is probably more expensive than just driving a used Nissan Leaf but the personal value of making the car up yourself is priceless.
 
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