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Discussion Starter #1
Hi, I’m considering converting a Porsche 924 to electric.
In essence, this is mainly a fact-finding mission to establish feasibility.
For those unaware, the car is a front engined rear wheel drive vehicle, utilising a torque tube which is mated to a rear gearbox and differential.

My knowledge is very, very basic with regards to EV conversions.

In an ideal world, and to make it worth doing, I need to have a range of around 250 miles.

I have seen various conversions utilising various motors and battery packs and was wondering what the general thought was on this?

I’m aware that there will be many other issues along the way but, at this point, it’s a question of quite simply, what’s the best way of turning it into an EV?
 

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I'm not that experienced here - but I will say that achieving your range figure is going to be tricky (Not saying it's impossible, but 250 miles in a small car with precious little room for batteries is going to be a squeeze), let alone very expensive.

Apart from that - I've seen a few 924 conversions browsing through EVAlbum.com... Not sure if any members who are active have done one or something similar - If there are, they'll be your best starting point!
 

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In any vehicle with a rear transaxle like this, I think it makes sense to consider packaging the motor and any required reduction gearing at the rear, leaving the engine space clear for a battery pack.

I thought that the 924 had essentially the transaxle from an aircooled VW bus, turned so the input faces forward; however, after some reading I realize that early and late ones had an Audi transaxle which is sitting in its normal orientation, but the opposite end of the car, and a few in the middle had a Porsche transaxle related to the 911's 915 unit. Anyway, the end effect is the same, with the transmission portion behind the differential portion. If the torque tube tunnel is large enough and there is clearance to the rear suspension torsion bars, a motor could be mounted to the front of the transaxle, almost certainly requiring the removal of the transaxle's bellhousing (details depending on which transaxle, but I don't think any of these transaxle s have a bolt-on bellhousing)... if you want to keep the transaxle. Various complete EV drive units might fit, replacing the original transaxle. There are other, more custom, possibilities.
 

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Converting a sports car is a great idea

BUT it's the required range and batteries that will kill you - squeezing 250 miles of range into a small sports car is going to be very very difficult

Possible solution

Go for a lower on-board range and use a trailer mounted battery for long distance operation - the trailer battery can earn it's keep as a home storage system when not being a range extender
 

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Discussion Starter #5
Cheers for the thoughts, like I said, I know nothing about EV’s,I just like the thought of the conversion, hence trying to get to info.

Although a relatively small vehicle, there is quite a large bonnet area and with the fuel tank removed, there is potentially more room to utilise around the rear diff if required?

Regarding batteries, I was considering buying a pack from a accident damaged vehicle so has to have a known product capable of being up to the job?
In light of this, what range could I sensibly expect.

Is there an agreed method of selecting a suitable motor? The car stripped of all its engine and accessories is going to be fairly light?
 

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Hi Mike
My tuppence worth on motors

DC (forklift motors) - cheap, very powerful - unsophisticated

New AC - expensive and wimpy or incredibly expensive

Out of an EV - Best overall - but more complex

For my next car I will probably buy a crashed EV and try to use all the bits

For you a crashed Leaf would be pretty good or if you were a bit richer a crashed Tesla
 

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Discussion Starter #7
Powerful and unsophisticated sounds good!
I’ve looked at Tesla batteries and from the very basic knowledge I have at this point, they seem to be the way forward as they seem to be the best out there?

From the basic reading I’ve done, the controller is possibly the most important part so probably best that at large part of my budget goes into that for the long term gains?
 

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924 or 924S? If the former you need to gobthe 944 route and get some discs on the rear. I have reinforced steel arms on mine so I ended up doing the 924 to early steel armed 944 disks but it bumped my track way out. Mine is a GT and I put the narrower rear 924 beam in mine (regretting it now of course) so I had to add the GTR arches. Do you have a manual rack, that would save you some work and makes life easy in the bay, it’s HUGE and shock and brake choice are endless. I currently favor the super cheap cayenne calipers and discs. I would for a road car swap the transaxle for a Tesla SDU. It’s self contained and leaves the boot free and clear, once you remove the gas tank and the floor there’s a cross beam you can suspend the motor off of while you fabricate the mounts.
I toyed with the idea of making it a single seater so I could put the batteries down each side of the seat but it was more work shifting the dash. Remaking the roll cage and while I have a few old formula 1 racks floating around it seemed a waste. I have the large motor in the rear because it’s designed to do a job, but the small motor would be a great install. You lose the torque tube and you have a cable speedo which later cars didn’t have. The battery’s are easily the expensive part and the most engineered in terms of cooling/heating. What ever advice given here will be redundant in 6 months as newer packs are available all the time. Possibly the best cost effective designed complete pack is the bolt one right now. It’s a good compromise of power density and output. The BMW i3 is also doing well so it’s worth looking around but pls. To spend 50% of your budget on the battery side. If I had to do it again I would do it that same way again right now, but newer tech is coming up used weekly.
 

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I agree that if going the route of using a motor salvaged from a production EV, and using the transaxle which comes with it (the motor and transaxle together are a "drive unit") the logical fit is a Tesla Model S/X drive unit, because the motor placement behind the axle packages best with the 924 suspension. A drive unit from the rear of a Tesla would fit better than one from the front (due to the motor height) and all you need is the smaller one from the rear of an AWD non-"Performance" car (thus the Small Drive Unit or "SDU").
 

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Discussion Starter #10
924 or 924S? If the former you need to gobthe 944 route and get some discs on the rear. I have reinforced steel arms on mine so I ended up doing the 924 to early steel armed 944 disks but it bumped my track way out. Mine is a GT and I put the narrower rear 924 beam in mine (regretting it now of course) so I had to add the GTR arches. Do you have a manual rack, that would save you some work and makes life easy in the bay, it’s HUGE and shock and brake choice are endless. I currently favor the super cheap cayenne calipers and discs. I would for a road car swap the transaxle for a Tesla SDU. It’s self contained and leaves the boot free and clear, once you remove the gas tank and the floor there’s a cross beam you can suspend the motor off of while you fabricate the mounts.
I toyed with the idea of making it a single seater so I could put the batteries down each side of the seat but it was more work shifting the dash. Remaking the roll cage and while I have a few old formula 1 racks floating around it seemed a waste. I have the large motor in the rear because it’s designed to do a job, but the small motor would be a great install. You lose the torque tube and you have a cable speedo which later cars didn’t have. The battery’s are easily the expensive part and the most engineered in terms of cooling/heating. What ever advice given here will be redundant in 6 months as newer packs are available all the time. Possibly the best cost effective designed complete pack is the bolt one right now. It’s a good compromise of power density and output. The BMW i3 is also doing well so it’s worth looking around but pls. To spend 50% of your budget on the battery side. If I had to do it again I would do it that same way again right now, but newer tech is coming up used weekly.
I have 3 cars to choose from, an S, a ‘83 5 speed and a ‘78 4 speed.

From your write up, the S is the more suitable vehicle but, I do have a complete 944 rear beam which I could fit to have the upgraded brakes if for any reason, if the N/A was a better base?

I think that fitting a complete rear axle from another EV could cause me some issues with regards to registration with the DVLA? It’s something I’d have to look into.
The GT is an interesting thought. I did a Carrera GT replica a few year ago. It would be nice to have another that we potentially quicker than the original!!
 

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For sure the S has better brakes and aluminium arms. The model s drive unit will replace the transmission and then you simply remove the torque tube and engine. That’s grossly simplified but you may get away with documenting it as a transmission swap. The 924 narrow track is quite nice and you gain little with the 944 in terms of space. I spent many years putting Rover v8’s into these cars and the 924s simply had the better brakes and was lighter, much lighter. The other thing is mine being a gt had a manual steering rack. Depending on your situation that might be ideal, I lived in inner London and parking was not the best, but my HSR never had power steering either and that was a beast to turn the wheel.
 
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