# 740i E38 ...EV maybe?



## rex1825 (Jan 14, 2014)

Hello guys,

Somehow I am lucky so to say, but I have my doubts and a lot of questions.
Firstli, I have a BMW 740i E38 model '01 for more years, and I am really fond of it ...honestly I'd like to never change it. And I did consider converting it to EV for long time, but since eMotors and Batteries are the biggest problem for this heavy car, I simply never got into it.

Now, I had really luck to get Tesla Model S 85kWh standard model in my possession, but problem is that car had really bad accident and I was lucky as said that battery, controller and motor it self didn't got anything from that accident. Those three things are in tact and I got them really cheap  

I am planing to use eMotor, battery and controller for my 740i and I do expect a lot of work here, but I am willing to do all that.

So here are few of my concerns and questions.
First thing, I wanted to limit torque to the eMotor to 440NM, I need confirmation if I need to mess around with controller and experiment a little bit, or is there easier way to do that?
Next thing, I wanted to use only first 6250rpms of eMotor, since that is what I got from my ICE, and it's the juiciest part of Model S motor itself. Shall I consider it different?
Now why am I willing to do it this way, well, I want to hook up eMotor to "ZF 5HP24" with "GS 8.60.2" controller. But transmission is made for max 440NM and ~6300rpm, which gave the M62TUB44 engine that was attached to it.
I know I'll have to sort some things off with car electronic, but I'm not concerned about that, just want to know if it is possible to hook up eMotor to that tranny and that at least it gives some life?

Another thing that I wanted to know, since I am little "not informed" regarding all this EV stuff, will I be able to get more range from battery if running that eMotor on 2500-3000rpm? Since while I was looking at mileage to speed chart it did look like Model S is giving most out of battery when running around 20mph and that is this rpm range. I know that aerodynamics won't be same, but is there any chance to get more range out of this solution? Or is it better to hook it up directly as it is in Model S (don't look at work needed, firstly it is range in my mind)?

One other thing, I did some preparations to the vehicle since battery pack is around 600kg and eMotor with other stuff is around 100-120kg.
My 740i had ~1890kg, I was planning to get 750iL suspension and brakes (2100kg vehicle) but I am also considering giving it Model S suspension and brakes (this is maybe better solution). I got engine, exhaust and fuel tanks out of the car and it has around 1450kg, so it is ideal so to say for transformation. I will however need to change a bit shaft of the car if gearbox will stay.

So, I just want your thoughts about all this, any suggestion and info that I asked for? I'm really not so deep in this eMotor stuff so I need help.

Cheers and thanks


----------



## Duncan (Dec 8, 2008)

Hi Rex
You are really lucky - those are excellent bits

In your shoes I would be looking at throwing away the IC bits and fitting the complete rear suspension and drive train from the Tesla

Using your old gearbox is unnecessary and will prevent you from utilising the power from the Tesla motor while sapping energy and reducing range

The reason that the Tesla gets more range at lower rpms is simply aerodynamics - drag goes up with the square of airspeed


----------



## rex1825 (Jan 14, 2014)

Duncan said:


> Hi Rex
> You are really lucky - those are excellent bits
> 
> In your shoes I would be looking at throwing away the IC bits and fitting the complete rear suspension and drive train from the Tesla
> ...


...well, if it's like that, I presume that energy consumption will be around 4x bigger running on 80mph regardless of eMotor rpms, and estimated range would go to around 350-400 miles.
Huh, it's a no go like on ICE, is it? 

Well, good thing is, I'll get rid of 50-60kg on tranny and shaft.

Now if I go with Model S rear axle and complete motor department, wheels on E38 are smaller then on Model S for about 1"!
E38 F: 235/50R18 R: 255/45R18
Model S one I got are F/R: 245/45R19
If I'm gonna use Model S tires, I'll need to get spare front right rim, since that side was heavily damaged. Also if I want to use Model S suspension rear, I'll need to get front up too, so again right side I'll have to get spare.
Well, I'll have less work to do, since I'll use whole electronic thingie from Model S, + suspension ground clearance.

But I think I'll stay with BMW's rims  And I'll get around 2% less max speed

Well, at least I got the main things.

Cheers...


----------



## dougingraham (Jul 26, 2011)

Your best bet would be to use the entire Tesla drivetrain. Driving the original transmission with the Tesla motor will reduce overall efficiency of the system. Using the BMW's original transmission and differential will most likely be a 5-10% loss of range although this might be the easiest way to do the conversion.


----------



## rex1825 (Jan 14, 2014)

dougingraham said:


> Your best bet would be to use the entire Tesla drivetrain. Driving the original transmission with the Tesla motor will reduce overall efficiency of the system. Using the BMW's original transmission and differential will most likely be a 5-10% loss of range although this might be the easiest way to do the conversion.


...I did see few more things, the overall aerodynamics of BMW E38 vs Tesla Model S is something like +10% to power usage. So from start, if I make direct swap without gearbox and all stuff, I'll get 10% less range due to the aerodynamics and additionally smaller wheel size.

Did get some numbers regarding Wattage needed for Model S to run on specific speeds 

km/h Wh/km
64 128
80 146
96 172
112 205
128 244
144 290
160 343
176 403
192 469
208 543

And simple calculation: speed(km/h) x usage(Wh/km) = Wattage(Wh)

I think I'm getting somewhere here already.

Reviewing all this, I think I can manage to get something around 15% loss in range, so estimated range would be around 500km driving around @ avg 80km/h on full battery load.

I think that's not bad at all.

...one thing more, eMotor that I have is the weaker version in Model S 85kW, so it is the 362hp/440Nm, so I can hook it up directly to transmission. And even with that additional loss of 5-10% through tranny, I'd get a 740i with 350+hp.
So max range would be around 450-500km.

Cheers...


----------



## Duncan (Dec 8, 2008)

But I think I'll stay with BMW's rims

Before you make that decision check that the BMW rims will fit,
Not so much now but rims used to have to get bigger to clear the bigger brakes

Not to mention the PCD (Pitch Circle Diameter) of the wheel studs


----------



## glaurung (Nov 11, 2009)

If you intend to use Tesla drivetrain make sure that rear axle can stand the load of big Beamer. Quite interesting conversion
Regards, Harri


----------



## tylerwatts (Feb 9, 2012)

Very interesting conversion Rex. Do you have some pictures of the 740 underneath and Tesla motor axle? I am thinking you can build a de Dion rear suspension, using the Tesla motor parts and BMW suspension. 

This sounds like a brilliant project, and I wish you the best!


----------



## rex1825 (Jan 14, 2014)

I'll try to record all what I'm doing, and I'll post links to my YT channel when all finished, it will however take some time to do it, so be patient 

I did however weight in midtime vehicle without, engine, fuel tanks and accessories, exhaust and tranny with shaft. Car has around 1350kg... 

But still I think giving a try with tranny. I'll get at least speeds up to 260-280 when needed 

Cheers...


----------



## Roderick (Dec 8, 2013)

How's the project coming along? 
I've got a same trans on my Jag which I'm going to convert in next year and this project has so much potential! 
btw, what's your plan with dealing using Automatic trans? (I believe they are)


----------



## rex1825 (Jan 14, 2014)

Roderick said:


> How's the project coming along?
> I've got a same trans on my Jag which I'm going to convert in next year and this project has so much potential!
> btw, what's your plan with dealing using Automatic trans? (I believe they are)


...well, for now, I was able to attach battery on the car, and tested it with some additional weight to see if new suspension will going to work. And all passed as I wanted, problem that I have right now is shaft of the car, need to bring it for about 15 cm higher, and that is my mayor problem right now.

Also did test the emotor connected to transmission over torque converter and it was all ideal. No problems at all and I was so pleased 
The reduce power emotor from Model S is perfect for this automatic transmission.

Hope I'll solve problem with battery and shaft, else I'll have big problems putting this together. Probably will need to do some additional work on the innerroom middle console and part where shifter is to be able to get shaft bit higher.

Cheers...


----------



## tylerwatts (Feb 9, 2012)

That sounds excellent Rex! Do you have any photos please? This is going to be a wonderful vehicle some day!


----------



## Roderick (Dec 8, 2013)

any progress with your build?? 
I am looking forward to pictures of your build too!


----------

