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Discussion Starter #1
I previously had a thread for a 944...but I had an opportunity to buy a 911 roller. It needs fenders, so why not put some big ones on it so I can get giant rear tires to hook up all that Tesla power...

Attached are some pictures of the car and the picture from the maker of the body kit.

The plan is still to use the two Chevy Volt battery packs. There is more room in this than the 944!
 

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I assume that the "RSR" part is a reference to the body kit, and this is not an actual 1973-1974 race car. What year or series of 911 is this? One of the pre-1989 (before the 993 type) cars, with strut front suspension and semi-trailing arm rear suspension, both with torsion bars?

(Edit note: corrected "trailing arm" to "semi-trailing arm")
 

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I assume that the "RSR" part is a reference to the body kit, and this is not an actual 1973-1974 race car. What year or series of 911 is this? One of the pre-1989 (before the 993 type) cars, with strut front suspension and trailing arm rear suspension, both with torsion bars?
I am MFOR1000's father and found the car on a local Craigslist ad. It is a '79 911SC so it does have the torsion bar suspension. It did come with the doors, the glass, the hood, the front fenders, seats, gas tank, bumpers, and assorted bits and pieces. He negotiated an excellent price for the car. As soon as I saw the ad, I sent him the link knowing that this was the type of car he was looking for.

He ordered an RSR kit that will make the car look like the white car in the photo above. Those fenders will allow him to install some meaty tires for better traction. It should be a fun car when it is completed.
 

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It is a '79 911SC so it does have the torsion bar suspension.
Thanks - that's the vintage I was guessing. The suspension may end up being important to how the EV components package in, but that vintage of 911 is very similar to a 944, so whatever was planned might work without much change.

It did come with the doors, the glass, the hood, the front fenders, seats, gas tank, bumpers, and assorted bits and pieces.
With any luck some of those (gas tank, and parts replaced by the RSR kit) can be sold to recover some of the cost. :)

He ordered an RSR kit that will make the car look like the white car in the photo above. Those fenders will allow him to install some meaty tires for better traction. It should be a fun car when it is completed.
I think it will need relatively wide rear tires just for good balance, since the rear-mounted motor and mid-to-rear-mounted battery will leave this car tail-heavy.
 

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I think it will need relatively wide rear tires just for good balance, since the rear-mounted motor and mid-to-rear-mounted battery will leave this car tail-heavy.
At this point, he thinks he can mount one set of batteries in the rear and the other set in the front with none in the middle. So the weight distribution may not be much different than a stock 911 which has nearly 60% of the weight on the rear.

However, the total weight will probably be higher. The front torsion bars are easily adjusted for height. Adjusting the rear torsion bars is more difficult. There are adjustable trailing arms available which would make the rear adjustment easier.
 

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At this point, he thinks he can mount one set of batteries in the rear and the other set in the front with none in the middle.
My understanding of the plan for the 944 (which has a tunnel for the drive shaft in its torque tube) was to basically duplicate the stock Volt configuration, with central tunnel and rear seat sections of the "T" pack. The 911 doesn't have much of a tunnel, so it makes sense to change to rear and front packs.

So the weight distribution may not be much different than a stock 911 which has nearly 60% of the weight on the rear.

However, the total weight will probably be higher. The front torsion bars are easily adjusted for height. Adjusting the rear torsion bars is more difficult. There are adjustable trailing arms available which would make the rear adjustment easier.
I agree that the total weight will probably go up (it always does in long-range EV conversions). With a front battery pack replacing the fuel tank, perhaps the net increase will occur mostly on the front axle, reducing the 911's significant rear weight bias (and minimizing the spring adjustment challenge).

Front pack placement should be interesting:
  • the stock fuel tank location is entirely ahead of the front axle and below the trunk floor; it is awkwardly shaped (not a problem for the fuel tank which is just shaped to fill the space, even moulding around the spare tire), and
  • the trunk (from the firewall to the front, including over the tank) has a very high floor due to the bizarre structure and brake master cylinder location of the 911 (and presumably a design to make a flat-floor trunk over the tank and spare).
Do you go too far forward in the awkward space, or too high in the trunk space... and perhaps gain a trunk in the rear?

Then there's this one...
A Tesla battery pack mutes this classic Porsche 911’s flat-six engine
... which fills the entire front trunk and tank/spare space. I can save you ten minutes of the video attached to that article - just jump to 2:28 for a view of the front pack (of Tesla Roadster modules), which is the only technical content of this typical two-guys-chatting promotional video.

The bigger rear tires are still desirable, even in a stock 911... although there are limits to that, as the usual "fix" for the oversteer which made 911's (and Chevrolet Corvairs) dangerous is a high roll stiffness bias to the front, which leads to lifting the inside front tire in hard turns, making the car into a three-wheeler (which needs sufficient front tire size to make this work).
 

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The bigger rear tires are still desirable, even in a stock 911... although there are limits to that, as the usual "fix" for the oversteer which made 911's (and Chevrolet Corvairs) dangerous is a high roll stiffness bias to the front, which leads to lifting the inside front tire in hard turns, making the car into a three-wheeler (which needs sufficient front tire size to make this work).
Like this photo I took at the 1981 Porsche Parade autocross in Asheville, NC!


 

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i don't know if Joey is on our DIY site, but he has done an excellent EV conversion of a 911. Here he described how he increased the diameter of the front and rear torsion bars to carry the extra weight of batteries, etc.

http://eporsche911.blogspot.com/2013/06/front-suspension.html

The front adjuster bolt is primarily used to preload the torsion bar during assembly and to make slight ride height adjustments to match left and right sides for alignment.
 

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Discussion Starter #11
Very helpful info guys!

I took a lot of weight out of it today. I removed the sunroof mechanism. I have a simple steel panel to bond back in it's place. That is supposed to buy me back about 30 lbs.

I also removed all the sound deadening material in preparation for sand blasting. That was pretty heavy too, I should have weighed it. I'm going to try to do without, as I'm used to pretty loud cars and there will be no engine noise. I don't know how bad the road noise by itself will be. I can always add sound deadening later if I get annoyed.

I also started doing recon on the rust situation. There was no rust under the sound deadening material on the pans...it looked like new under there.

It has some rust at the rear attachments of the front fenders and at the rear bases of the doors. From what I've read, these are typical spots. This is where water and dirt get trapped. It also has some at the base of the windshield, especially on the left side.

I did a decent amount of cutting on the left fender attachment per the picture. I ordered another fender attachment panel since the lower part of it would be difficult to fabricate. I'm going to make my own patch panel for the inner part I cut out. Fortunately, the inside of the frame and the rocker were in excellent condition.

The right side fender attachment may only be surface rust, I'm not going to cut it out. I'll see what it looks like after blasting.

The rear bases of both doors were pretty bad. I had to cut a lot out. I'm going to wait to do more until after I cut the quarter panels off for the new ones. I think I'm going to wait to blast till then, since with those quarters gone we'll really be able to clean it up in there. I also think I'm going to make a shield to prevent dirt from getting in there...it was packed tight between the panels. From these holes, I could see inside both rockers at the rear and I believe they're in great shape.

I'll do what I have to to make this thing solid. I am considering putting a cage in it....there goes all my weight savings!
 

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I also removed all the sound deadening material in preparation for sand blasting. That was pretty heavy too, I should have weighed it. I'm going to try to do without, as I'm used to pretty loud cars and there will be no engine noise. I don't know how bad the road noise by itself will be. I can always add sound deadening later if I get annoyed
I had a race-prepared Honda with most of the sound-deadening material removed. I think you'll be adding at least some of that back. ;)

I'll do what I have to to make this thing solid. I am considering putting a cage in it....there goes all my weight savings!
I hope you're able to leave the decision on the cage, or at least the details of the design, until you have a battery configuration worked out, so that everything works together.
 

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The front adjuster bolt is primarily used to preload the torsion bar during assembly and to make slight ride height adjustments to match left and right sides for alignment.
Very good point. :) Torsion bar adjustments are like changing the threaded collar setting for the coil spring on a coil-over shock, or changing spacers between an axle beam and leaf springs. It does not change the stiffness of the spring (although it can change the effective stiffness a bit by changing the leverage), and if the suspension is carrying significantly more mass the spring (and shocks) should be stiffer.
 

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i don't know if Joey is on our DIY site, but he has done an excellent EV conversion of a 911.
...
http://eporsche911.blogspot.com/2013/06/front-suspension.html
Interesting project - thanks for the link. :)

Unlike most air-cooled VW and Porsche conversions that I've seen, this one uses the space on each side of the electric motor (in the stock engine location) for batteries (and even a few above the motor), and as a result - even though this project from a few years ago is using prismatic LiFePO4 cells - it does not need to use any rear seat or trunk space for battery.

Of course packaging with be different with the Tesla drive unit (instead of DC motor and stock transaxle), and with Volt batteries instead of the prismatics, but it's still an inspiration. Unfortunately, while it's almost possible to imagine a full Volt pack in the front (consuming all of the fuel tank and trunk space), I certainly don't see another one in the back with a motor there as well... so I assume that the back seat will be sacrificed.
 

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Discussion Starter #16
Wow, nice AC kit. I'll definitely consider that when the time comes. Frankly, I'll be glad when I'm worrying about stuff like that! I don't suppose you have a 380V heat version?

For heat, a friend suggested using aftermarket seat heaters. He thought those might be enough to get by for a while.

Today was spent reorganizing the garage for this project...the clutter was driving me crazy...

After that, I welded up a cradle for the Tesla motor to use on my transmission jack. Attached is a picture for anyone interested in doing the same. I tried to keep the CG in line with the shaft of the jack so it will be stable. I'll put the drive unit on it tomorrow and see if I need to add any more support.
 

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Discussion Starter #17
I tried out the cradle for the Tesla drive unit. It worked great. Very stable. The chain ran over the front and it didn't move.

I mocked up the position in the car and took some pictures. It fits in there pretty easily. The driver's side shock is close, but I think it will be fine. I'm just going to need to make a low profile mount for that side.

I placed the bottom of the motor at floor level and where I think the axles will be at ride height. Nothing precise yet, just getting an idea what I'm in for.

For the final mockup, I'll need the suspension with tires and wheels and no torsion bars so I can set the suspension to ride height. I may drill these shocks so they won't produce any force and allow me to use them more easily for mockup.

It looks like I will be able to get all three modules from one Volt pack back there. The big one behind the motor angled up to the rear bumper. The second largest one on top of the motor, and the small one behind and on top of the big module. I may need to angle or lay down the small one to have enough room to clear the decklid.

I hope to make a sealed box to enclose all the batteries. Then have airflow go through the grill on the decklid for the motor and battery coolers. I think I can make the bottom of this box double as a diffuser to clean up the aero under the rear of the car. I may even make a panel to go under the motor to the floor pan to clean things up more and protect the motor.

It looks like there is lots of room in front of the motor for the cooling pumps.

I should also have room next to the small battery in the back up top for a contactor and electronics box that will be easy to get to.

I also found 'the guy' to do the blasting today. He does work for all the local Porsche shops. He has even blasted parts for the all aluminum Gmund coupe that was rebuilt locally....certainly he can handle a little 911 SC... He said he doesn't need a rotisserie. He can lift the car high enough with some padded forklift arms to blast the underside. I'm going to make some casters for it so I can take the suspension off. I don't think I have a lot of work to do under there.
 

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For the final mockup, I'll need the suspension with tires and wheels and no torsion bars so I can set the suspension to ride height. I may drill these shocks so they won't produce any force and allow me to use them more easily for mockup.
You might consider pieces of threaded rod (with a cheap rod end on the bottom) as shock replacements, to hold the suspension at any desired position. You could put some tubing around it to model the shock body for clearance. Just possible ideas...
 

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It looks like I will be able to get all three modules from one Volt pack back there. The big one behind the motor angled up to the rear bumper. The second largest one on top of the motor, and the small one behind and on top of the big module.
I'm puzzled... the first generation Volt battery has 9 modules (7 large + 2 small), and the second generation Volt battery has 7 modules (3 large + 4 small). So what does "all three modules from one Volt pack" mean? By "pack" do you mean just one part of a Volt battery, either the part in the tunnel or the part across the back?

Also, you're talking about three sizes of module:
  1. The big one
  2. The second largest one
  3. the small one
... but in any given generation of Volt, there are only two module sizes.

For reference, here's a description from GM of both generations of Volt battery:
Chevrolet Volt Battery System

________________________

Edit:
I think I have this figured out. You're probably using the Gen 1 Volt battery, which has
  • seven large modules of 12s3p = 36 cells (in 19 plastic frames per module), and
  • two small modules of 6s3p = 18 cells (in 10 plastic frames per module)
and
  1. seeing three large modules plus one small module bolted together across the back and calling that the big module (42s3p = 126 cells)
  2. seeing two large modules plus one small one bolted together at the front of the tunnel and calling that the second biggest module (30s3p = 90 cells)
  3. seeing two large modules bolted together at the back of the tunnel and calling that the small module (24s3p = 72 cells)
... for a total of 96s3p = 288 cells (and 196 kg), a full first-gen Volt battery. I suppose the boundary of what to call a "module" is determined by electrical connections by GM (to get 9 modules), but it could be done by physical construction (to get 3 modules).
 
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