I've recently just done a complete EV race car design project on behalf of a well known but not so big manufacturer, can't name them for now unfortunately due to NDA. You guys are definitely on the right track with used motors, because lightweight and efficient automotive use motors are not cheap. I think 5000-7000gbp is a fair target budget for a conversion like this.
The main things to consider are: what do people interested in this project and this budget want? Performance, range, weight and space lost would be the main things I consider.
Let's focus on the 2011 Leaf powertrain as an example. We will first go through some nerdy math so we can put the performance into perspective.
1. Performance, quickest accelerating off the shelf
A2 is a FSI about 9.8s 0-60. 110hp, 155Nm. 5 speed manual. You need to use 3 gears to reach 60mph. For how quick it can accelerate we need to consider the gear ratios and final drive which will give us axle torque. We won't calculate wheel torque since we aren't changing it.
Torque curve here
https://www.audiworld.com/news/02/geneva/a2/a205.jpg
Final drive GSK transmission: 3.933:1
1st gear: 3.455, 2nd: 2.095, 3rd gear 1.387
Axle torque at maximum engine torque would be 2106, 1277 and 846Nm respectively at 4500RPM
Since the torque curve isn't flat, for 2000RPM from the graph, it is roughly 82.5% of the above axle torque figures. 89% for 3000RPM and 5500RPM. You get the idea.
The Leaf uses a 110hp, 280Nm motor. Single gear final drive 7.937:1 direct input form motor I assume (common).
Torque curve (all motors will look like this due to back EMF), EV's are most efficient at lower speeds:
https://www.researchgate.net/profil...r-parameters-for-a-Nissan-Leaf-vehicle-20.png
To figure out where this motor operates at 60mph, we need tire size: 631mm. Result: approximately 6500RPM, motor torque at this point= 120Nm.
Time to figure out the axle torques at different speeds.
0-26mph: Axle torque = 2222Nm
40mph: 1388Nm
60mph: 952Nm
Now what is the point of these axle torques, it is to give you a roughly idea of how the car feels at these different speeds. Using 1,2,3 gear for the A2 because they would be the gears you use for max acceleration these speeds listed above.
Leaf motor has more torque, of course. But I wanted you guys to know that it's not a huge difference at the axle.
To calculate acceleration, we still need to figure out the approximate weight of the vehicle.
A2 FSI listed unladen weight 1085kg, take 40kg out for fuel, 15kg for fuel system, and let's assume 245kg for all engine and gearbox stuff which we will remove, puts us at a nice 300kg. We will keep the 12V battery for accessories. Our car now sits at 785kg.
https://www.marklines.com/en/report_all/rep1786_201811 , 2010
battery pack assembly ~300kg, half of which are actual batteries, other half are wiring, protection plate, mounting system etc
https://www.quora.com/Why-are-electric-cars-so-heavy-The-Nissan-Leaf-is-1-470-kilos , the weights of the charger, inverter and motor were 27kg, 15kg and 82kg respectively.
We also need a dc-dc converter to deal with the 12V system, ~30kg and another set of wiring to mate to the A2 ~10kg.
We also need a cooling system for the motor, inverter and battery pack, so let's call it 50kg
Now I'm sure we probably need a few more bits, and to be accurate and conservative lets call it another 35kg
Total weight ~1300kg < this is assuming we put the whole battery system in somehow, perhaps distributed in engine bay, in front footwells, in place of fuel tank, in bottom of boot, I'm sure we can fit it somehow, or let's at least assume so for sake of this (already spent an hour typing).
We are about 220kg lighter than the first Leaf! I think it's reasonable, maybe slightly lower than reality cuz we would need some brackets and stuff. But close enough, let's move on.
I'm excluding driver weight.
So time for some more math. F=m*a, acceleration = Force/mass, Force is calculated from Torque /distance, distance in our case is wheel radius which will not be changed, and since we are just comparing for how much acceleration boost we will use torque to visualize it. We will call this the acceleration factor and not confuse you with units, but the higher the better.
FSI A2 1, 2, 3 gear, 1085kg
Max acceleration factor: 1.94, 1.17, 0.78 for the gears respectively at 4500RPM
3000RPM, 5500RPM: 89% of above (1.72, 1.04, 0.69)
Can calculate for the other RPMs yourself if you want but most RPMs will fall in this region for we when we pass at max acceleration.
Leaf powered A2: 1300kg
Max acceleration factor:
0-26mph: 1.71
40mph: 1.07
60mph: 0.732
So what can we conclude from this? The FSI A2 can provide a punchier feeling at specific RPM and speed ranges in the first three gears and accelerate quicker there. However the Leaf A2 is very similar and even better at 60mph than the FSI. The EV will not require any gear shifts and will be quite useful for whenever power is demanded, not everyone can instantly and perfectly downshift their A2 to the correct gear. I estimate overall, the Leaf motor will feel just a little quicker than the FSI but accelerate to 60mph quicker by 1 second to ~8.8s because the leaf which is 220kg heavier at 1520kg does 9.8s. I personally is happy with this performance, very reasonable.
Batteries and Range:
Since the Leaf 2011 model only has 24kWh and does 109miles on the NEDC loop, and we want people to support this project as much as possible, we should at least target this.
With a similar Cd and likely similar frontal area, we can assume similar drag.
Let's be optimistic and say 85% range is still available from these used batteries, now we have 109*0.85= 92.65miles. This is what the ~150kg of battery can provide for the total weight 1520kg in today so let's do a rough factor estimate:
150kg battery = 92.65miles for 1520kg
1300kg/1520kg = 0.855
92.65miles/0.855 = 108.36miles, since the powertrain isn't optimized for the A2, let's just say it it can do 100miles conservatively
100miles I think is a range that is realistic and worth doing the work for, for people who drive their A2 a lot (short trips) and love A2s.
Further:
Batteries have come a long way since 2011, many things need to be considered, battery chemistry for safety, power density, energy density and cost. Tesla model 3 cells are quite a good balance. But I think it will be quite the liability to make our own battery packs, especially consider the consequences of battery failure and considering the relative ease of obtaining proven safe packs from a Leaf.
What I am most inclined to do (as a Motorsport Engineer)?
I would get a Nissan Leaf, literally move all the batteries, cooling pump, motor, gearbox and anything drivetrain, powertrain, battery electrical into an A2. Make the HV battery able to charge an A2 12V battery and keep the A2 12V battery. I would use the Leaf's throttle pedal, brake pedal assembly and cut up the floors of the A2 (space frame so the floors are super thin skins, can easily make new removable covers) to mount as much batteries as possible under the car, one pack in the boot, one under the bay if possible. I will try to fit all of the batteries in otherwise I don't think it's worth my money or time, the batteries themselves are only 150kg anyways.
The complexity we can minimize by going this route is maintaining OEM Leaf motor control, thermal control (very important), battery protection and drivability. This is not something you can make as good as OEM or as nearly as safe yourself. The last thing you want is having your 13000GBP A2 catch on fire and have to explain to insurance about it.
Would I consider other cars?
Not really, not for the price targets we have for now at least. Maybe an i3, but you're paying more for the carbon fibre if anything..
What do I think it will cost?
5000GBP for a Leaf with good batteries, 1000GBP for Cooling system pipework and radiator, 500GBP for a used welder, 500GBP for metals, 2500GBP for misc. All these rates are based on if I do my own work. No clue how long it will take (probs 300+hours) and if we assume 50gbp/hr, it's definitely not worth paying people to do this. These are based on experience in putting engines in cars where they don't belong ?
Would I pair other batteries with a Leaf motor?
Maybe newer Leaf batteries, but not other cars cuz of the reasons above.
Took me 2 hours to type it out, hope it helps haha. Needed a break from my school work?.
*disclaimer, all of above are my personal opinion for the sake of a discussion, all work should be carried out by and under consultancy of EV and HV system professionals.
) The converted A2 would still have the poor quality of ride, as has been mentioned and certainly when compared to the BMW i3
