DIY Electric Car Forums banner
1 - 11 of 11 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
So I am new to this forum and working on cars in general, but given extra hobby time by the current climate, I've been reading up on how cars work and how I might fulfill my dream of having a hybrid sports car.

The plan would be to get a 2020 Toyota Supra and install a ZF plug-in hybrid transmission. The new Supra is a rebadged BMW sharing a similar engine and identical transmission to a regular BMW sedan, and BMW makes hybrid versions of their sedan using that transmission, which means I'd be able to find one off of eBay. The speakers behind the rear seat (which, incidentally, the reviews describe as "terrible" anyways) would be removed make room for batteries and the power electronics. A pair of the many fake vents would be opened up to cool the battery pack. A whole new ECU would be needed to control this system, but hopefully I could remap one off of a hybrid BMW.

The goal of the whole exercise would be to make a borderline supercar that would rival an NSX in performance without breaking 6 figures total, all the while maintaining enough trunk space to roadtrip with.

I don't plan on doing this any time soon since I'm currently an expat with no room for working on cars. I have a masters in electrical engineering and can program in a couple of languages, so I don't think the steps identified so far are insurmountable. How daft of an idea is it?
 

·
Registered
Joined
·
187 Posts
That sounds very awesome, very expensive, and pretty tough. Mostly in terms of controlling the transmission and packing everything into a small space. Since you're already thinking about BMW transmissions, why not get one of their batteries? 9KWh (fairly small), sufficient power for the hybrid transmission, and nice and dense so that they might actually fit.

Looking around at ZF hybrid transmissions. I found this: BMW’s iPerformance plug-in hybrid electric vehicle (PHEV) powertrain architecture – x-engineer.org
They quote 83Kw with a maximum of 250Nm. Not bad numbers. Motor has constant torque to 3170RPM, at which point it hits constant power.

Unlikely to rival an NSX (that has 500HP from the engine) but still good power.
It looks like the motor gets coupled directly to the engine with a couple clutches in there too, not exactly a simple drivetrain but it could work.
 

·
Registered
Joined
·
532 Posts
Your car is the same weight as a Bolt EV, which comes with a 130kW motor, iirc. So, it'll suck compared to a Bolt for acceleration and top speed.

Figure out what you want. If it's NSX performance, the ZF is a nonstarter and you need to start thinking about getting a 400-500HP motor in there. Yes, there's the torque of a lower horsie emotor, but what's the point if it can only make a run at Bonneville's golf cart speed record?
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #4 ·
That sounds very awesome, very expensive, and pretty tough. Mostly in terms of controlling the transmission and packing everything into a small space. Since you're already thinking about BMW transmissions, why not get one of their batteries? 9KWh (fairly small), sufficient power for the hybrid transmission, and nice and dense so that they might actually fit.

Looking around at ZF hybrid transmissions. I found this: BMW’s iPerformance plug-in hybrid electric vehicle (PHEV) powertrain architecture – x-engineer.org
They quote 83Kw with a maximum of 250Nm. Not bad numbers. Motor has constant torque to 3170RPM, at which point it hits constant power.

Unlikely to rival an NSX (that has 500HP from the engine) but still good power.
It looks like the motor gets coupled directly to the engine with a couple clutches in there too, not exactly a simple drivetrain but it could work.
I haven't gotten to the battery in my planning, partly because I don't have much of an idea of what constitutes a good or sporty battery. If the BMW battery is usable, it would be nice since I could look for a salvage title BMW 330E and pull out all the pieces. It would definitely be cheaper than buying the parts individually.

The NSX has 572 BHP while a stock Supra has 335 BHP (nominally, the community says Toyota is sand bagging and it's more like 390). With some intake and fuel injection bits plus some tuning, I've seen people get them above 450 BHP. Combined with an electric motor, I'm hoping to get around ~550 BHP, with 200 kg of weight difference between a stock NSX and Supra to get there. Not enough to beat an NSX is a straight up genital measuring contest, but close enough to satisfy my inner child.

Your car is the same weight as a Bolt EV, which comes with a 130kW motor, iirc. So, it'll suck compared to a Bolt for acceleration and top speed.

Figure out what you want. If it's NSX performance, the ZF is a nonstarter and you need to start thinking about getting a 400-500HP motor in there. Yes, there's the torque of a lower horsie emotor, but what's the point if it can only make a run at Bonneville's golf cart speed record?
Read again, I'm trying to put both a 450 BHP motor and a ZF transmission mounted motor in there :)
 

·
Registered
Joined
·
187 Posts
I haven't gotten to the battery in my planning, partly because I don't have much of an idea of what constitutes a good or sporty battery. If the BMW battery is usable, it would be nice since I could look for a salvage title BMW 330E and pull out all the pieces. It would definitely be cheaper than buying the parts individually.

The NSX has 572 BHP while a stock Supra has 335 BHP (nominally, the community says Toyota is sand bagging and it's more like 390). With some intake and fuel injection bits plus some tuning, I've seen people get them above 450 BHP. Combined with an electric motor, I'm hoping to get around ~550 BHP, with 200 kg of weight difference between a stock NSX and Supra to get there. Not enough to beat an NSX is a straight up genital measuring contest, but close enough to satisfy my inner child.
Very cool. I did read about the low HP rating, that's very Toyota of them. You will probably end up adding ~200kg of stuffs, between batteries, charger and bigger transmission.

BMW battery is quite usable due to its high power output, there's even some software that can talk to the modules and check the balancing and voltage levels. You need to be sure to get a 96 cell/360 volt battery, anything less will hamstring your motor.

Do you know if the transmission will actually fit? I'd be concerned about whether it will match up to the motor and how the clutches work - there doesn't seem to be much info in that department.
 

·
Registered
Joined
·
6,200 Posts
The feature of the NSX which this system would not duplicate is driving the front wheels - the NSX has a dual motor drive unit on the front axle. That's more important for handling and for energy recovery by regenerative braking than it is for acceleration, but it's still a factor to consider.
 

·
Registered
Joined
·
6,200 Posts
Looking around at ZF hybrid transmissions. I found this: BMW’s iPerformance plug-in hybrid electric vehicle (PHEV) powertrain architecture – x-engineer.org
...
It looks like the motor gets coupled directly to the engine with a couple clutches in there too, not exactly a simple drivetrain but it could work.
One additional clutch - just between the engine and the electric motor. In this version of the ZF 8HP transmission, the motor physically occupies the space which would normally be taken by the torque converter and torque converter lockup clutch, and the job of allowing drive by the engine when the road speed is too low for the engine to run is taken by the "launch clutch", which would presumably just be one of the transmission's normal shift elements upsized for the task (I think it might be clutch A) and it doesn't have as much to do in starting as a normal manual transmission clutch because the car normally launches in EV mode. This makes the hybrid 8HP simpler than but significantly different from the normal 8HP, and is the reason that Scarborough's plan of swapping the complete transmission is the more practical alternative to just adding an electric motor.

One detail that I noticed in a ZF product page:
Only 30 millimeters additional installation space compared with the standard transmission
So it will swap in reasonably, but the transmission mount will not likely line up.
This may only apply to the "plug-in hybrid" version (which has a bigger motor than the "full hybrid" version), but it's worth checking. The variations are described in ZF's transmission technology brochure.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #8 ·
One additional clutch - just between the engine and the electric motor. In this version of the ZF 8HP transmission, the motor physically occupies the space which would normally be taken by the torque converter and torque converter lockup clutch, and the job of allowing drive by the engine when the road speed is too low for the engine to run is taken by the "launch clutch", which would presumably just be one of the transmission's normal shift elements upsized for the task (I think it might be clutch A) and it doesn't have as much to do in starting as a normal manual transmission clutch because the car normally launches in EV mode. This makes the hybrid 8HP simpler than but significantly different from the normal 8HP, and is the reason that Scarborough's plan of swapping the complete transmission is the more practical alternative to just adding an electric motor.

One detail that I noticed in a ZF product page:

So it will swap in reasonably, but the transmission mount will not likely line up.
This may only apply to the "plug-in hybrid" version (which has a bigger motor than the "full hybrid" version), but it's worth checking. The variations are described in ZF's transmission technology brochure.
Interesting. How do people normally handle swapping a larger transmission? A shorter driveshaft? Or prodigious application of a hacksaw?

Also I recognize an electric car forum might not be the best place to ask about transmissions...
 

·
Registered
Joined
·
532 Posts
Meh...it's just gears.

I've had gracious auto wreckers that let me peruse their driveshafts to get the right lengths when I put a larger trans in for my ICE swaps - barring that, any driveline shop is adept at shortening a driveshaft and balancing it.
 

·
Registered
Joined
·
6,200 Posts
How do people normally handle swapping a larger transmission? A shorter driveshaft? Or prodigious application of a hacksaw?
Yes, a shorter propeller shaft is likely required, and as remy_martian suggests there are both swaps and service shops to address that.

The other aspect is the transmission mount. Most conversion projects involve some amount of bracket fabrication and body adaptation.

Also I recognize an electric car forum might not be the best place to ask about transmissions...
True, but it is not unusual for a conversion to involve a change in transmission, so this sort of mechanical challenge - even though it is not specific to electric drive systems - does come up in projects discussed in this forum.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #11 ·
The other aspect is the transmission mount. Most conversion projects involve some amount of bracket fabrication and body adaptation.
I can't seem to find a diagram or even a video to see what the transmission mounts looks like on a Supra, and having never properly worked on a car I can't picture it either. There is a part number for Supra transmission mount (rear) on Toyota's website, but it's grouped together with other drivetrain mounts with a diagram pic that looks suspiciously like a B58 BMW engine mount. The 330E transmission mount and the M340i tranmission mount (which uses the same engine and transmission as a Supra) look identical though. I suspect there's still work that needs to be done? The amount of clear and technically in-depth transmission swap videos on the internet aren't great.
 
1 - 11 of 11 Posts
Top