# 1985.5 944 Tesla Swap Megathread



## Classic Style (Nov 28, 2020)




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## BKaye (Nov 18, 2021)

Hey @Classic Style! Would love to hear more about this build as I'm hoping to start a similar project in the next few months. Did this thread move elsewhere or is there more info somewhere else I could check out? Thanks!


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## gregski (Sep 6, 2011)

"Megathread" your modesty precedes you, lOl, I'm in, ha ha


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## Classic Style (Nov 28, 2020)

gregski said:


> "Megathread" your modesty precedes you, lOl, I'm in, ha ha


HAHAH! My ambition precedes me more like  Oh well. 



BKaye said:


> Hey @Classic Style! Would love to hear more about this build as I'm hoping to start a similar project in the next few months. Did this thread move elsewhere or is there more info somewhere else I could check out? Thanks!


I haven't added anymore info anywhere else honestly. Work, life, and project have taken up most of my time, so I haven't posted, or made as much progress as I'd like.

Here's the general update:








This was the position of the motor as it was previously mounted. That position was a mistake, and it needed to be rotated forward about 10 degrees to properly feed the lubricant pump inside the differential case. We did that, and thus lowered the motor about 1 cm from it's previous position. This necessitated the rear battery box to be lifted by 2 cm to give proper clearance for the motor torque-shifting under acceleration so it didn't impact the battery case and cause long-term problems. 









We picked up those fancy differential-to-930 adapters from Zero EV UK. Much cheaper than anywhere else, even having them shipped to the US and paying in GBP instead of USD. We picked up the CV joints off Ebay, and they all came with annoyingly short bolts, so we had to buy an entire set of bolts that were 60mm instead of the 50mm that came with the CVs. I mean, seriously, 2 threads were showing on the back side, nowhere near enough to handle the torque this thing's gonna be dishing out. Be mindful of that.

We also had to get special 944 to 930 adapters from Lindsay Racing out of OKC. You have to call them to special order them. Took about 3 weeks to get. I think we cut the new 930 axles to 22.5" in length, but definitely do your own measuring.









Next up, we worked on getting the Tesla Model S (and I guess BMW) iBooster master cylinder assembly hooked up to the car. Fun fact: the 944 vacuum booster mount to the firewall has _the exact same bolt pattern_ for the brake booster as the iBooster does. Score! The only modification we had to do was change the plane of the mount to be more parallel with the firewall than it is by default. What you see in the photo is pre-modification. Also, you need to grind the nipple off the end of one of the two bolts from the ibooster, otherwise it contacts the firewall and doesn't sit square. I'm talking about .075" off the end of the bolt. Nothing to write home about.









SimpBMS: We chose to use the SimpBMS solution on this car, and are almost done wiring it up. I found a super handy post from the solar panel forum (blanking on it at the moment) that gave a good breakdown of the wiring, cause I really lacked a basic understanding that was necessary to understand SimpBMS' manual. It's like the manual was written with the intent to be exclusionary, even though it's open source.  
Anyway, I picked up a bunch of these audio-style jacks that allowed me to wire through as a bulkhead connector, and easily disconnect the battery boxes from one another. I suck at soldering, but made it work. I hope to have SimpBMS wired up in the next weekend or two as time allows.

Also, I'd like to take this moment I suck at aluminum fabrication and welding. That is a tough trade to get good at. Mad respect for anyone that can do that and make it look easy.









HVAC: We were planning on installing and using a universal A/C and heater core system you can find easily off eBay for a few hundy. Those turned out to be more work than adapting the 944's OEM system. Here's the plan:

Wire up a battery coolant heater and tiny pump inline with the heater core that can be switched on via the polykup vehicle control to generate heat. Yes it's less efficient than the PTC, but I don't care at this point. Making an entire HVAC system around one component is less efficient for me given my previous comments about welding and fab.
Use the Tesla High voltage A/C compressor (PWM edition) controlled by an Arduino that receives CAN signals from the polykup and interprets them into a PWM signal. Aside from the CAN interpreter aspect, I already have an Arduino coded up and successfully outputting the PWM signal to control the A/C compressor. I have shared that code elsewhere on this site. 
Replace all the OEM solenoids and valves with Arduino-controlled, can-interpreted servos to do my bidding (buahahaha).

Steering (no photo, sorry)
Got the Prius column mounted, not really happy with the setup at the moment. Was going to use the Prius stalk, but I think I'm going to opt for using the 944 stalk instead, even though I've completely gutted the wiring for the car. I had this idea of using arduinos to manage all the signals from the stalk and run it through a controller, but I found I'm creating too many failure points in an already highly customized vehicle. (in Yoda voice) Need to simplify is strong with this one.









Trial fit the dash in without the stalk on the column. Yeah, the vinyl's cracked to all hell. It wasn't that bad when I took it out of the car almost 5 years ago (cries), but I'll do something about it later when the car is running. Maybe. I'm going to 3D print a replacement plate to cover the A/C/Heat controls cause I'm going to control all of that through the polykup.









Here's a beautiful bastardized photo. 944 car, white face gauges, Toyota prius electric power assist column, 944 stalk (no cruise) and a steering wheel adapter from Toyota (which barely fits at all) to an NRG quick-disconnect steering hub. ♥ Now I have to find the plastic housing that goes over the stalk, and make some sort of set-screw or retaining clip to keep it from spinning on the column over time. 

I think that's all for now.


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## 57Chevy (Jan 31, 2020)

Neat project. Have you driven with the iBooster working? Somebody online said that the ABS module works out the pressure which is needed for load feedback, not sure if this is true. Haven't seen anyone drive with one to see how the pedal feels.


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## brian_ (Feb 7, 2017)

Classic Style said:


> Next up, we worked on getting the Tesla Model S (and I guess BMW) iBooster master cylinder assembly hooked up to the car. Fun fact: the 944 vacuum booster mount to the firewall has _the exact same bolt pattern_ for the brake booster as the iBooster does. Score! The only modification we had to do was change the plane of the mount to be more parallel with the firewall than it is by default...


It's not just Tesla (all current models) and BMW...
iBooster donor vehicles
This list is not complete - it doesn't even include BMW. 

Since the iBooster unit is mounted at various angles from horizontal in different vehicles (which changes the reservoir), as well as having different mounting bolt patterns (and possibly different cylinder bores), it's worth looking at what is available to find the best match in a particular conversion. It may also be worth considering other electrically-boosted master cylinders (some are listed in the link above).


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## Classic Style (Nov 28, 2020)

Very cool resource. Thanks Brian. I wish I'd known about it prior to starting this journey  

57Chevy, no I haven't driven with it yet. Project is still in the mid-stages. I'll let you know what I find when I can though.


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## brian_ (Feb 7, 2017)

57Chevy said:


> Have you driven with the iBooster working? Somebody online said that the ABS module works out the pressure which is needed for load feedback, not sure if this is true.


Anyone considering the iBooster might find this informative (or at least entertaining):
Inside Tesla's Brake Booster. And How To Use It On Any Car.

A braking system using all of the capabilities of the Bosch product line would include the iBooster, the ESP® hev module, and an ABS controller. Bosch's integrated power brake can be used instead of an iBooster and ESP® hev module. Any of these combinations potentially involves additional sensors and programming... but the iBooster can work by itself, without needing ABS (but also without integrating with regenerative braking).


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## 57Chevy (Jan 31, 2020)

brian_ said:


> the iBooster can work by itself, without needing ABS


It appears to operate in limp/failure mode which is ok I guess for basic applications. I had a look at the can messages and it outputs a flag for pedal at rest-position and also a value that increases with pedal movement so regen should be fairly straightforward based on this value. 

The ABS/ESP module is a bit of an unknown as to how it operates with parts of the system missing. The ESP side requires steering wheel position which comes from the indicator stalk module (SCCM) but I don't know if the ABS can operate stand-alone from the ESP since it doesn't need steering position. I hope it can as I need ABS but not ESP. Alternatively the Bosch Motorsport ABS module is exactly the same thing with different firmware so that might be a plan-b if the OEM ABS isn't going to play nicely

It does make me wonder when OEMs are going to realise that four motors can provide all the brake, skid, traction and stability control functions, and dispense with friction brakes entirely.


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## brian_ (Feb 7, 2017)

57Chevy said:


> It does make me wonder when OEMs are going to realise that four motors can provide all the brake, skid, traction and stability control functions, and dispense with friction brakes entirely.


When driving safely doesn't require redundancy, and everyone trusts electronic systems in cars to be infallible. 

But seriously - most EVs don't have adequate regeneration power to provide sufficient emergency braking ability, from all speeds and at all battery charge levels. Many are only 2WD, and a second drive unit is much more expensive and heavier than a pair of brakes.

Friction brakes in any vehicle (EV or not) could be simpler if electrically-operated calipers were used, such as the Siemens VDO Electronic Wedge Brake or the electromechanical wheel brake of the 2013 Audi R8 e-tron. That would eliminate all hydraulics including the master cylinder, but even that has not commercially succeeded yet, presumably because there isn't enough trust in the electronics. Electromechanical calipers are so far only used for parking brakes.

OEMs are well aware of what can be done... and just as importantly, what would be required to do it.


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## Classic Style (Nov 28, 2020)

Do you guys find it necessary to run a separate contactor for your HV distribution, or do you feed off the motor side of the contactors?


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