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"New" EV: 1973 Saab Sonett Conversion

113574 Views 121 Replies 20 Participants Last post by  Aethora
1973 Saab Sonett Conversion w/Nissan Leaf Drive System

Status Update 1/12/16:
- Obtained a running/driving salvage 2012 Nissan Leaf
- Completed Leaf teardown, demonstrated system functioning outside the Leaf
- Removed outdated 96V DC PbA based system from Sonett
- Sonett teardown to frame nearly complete

- Make more accurate measurements of Sonett frame, and Leaf components to finalize placement and fabricate necessary mounts and brackets.
- Initial focus will be to make bare Sonett chassis drivable / functional for continued testing of Leaf Drive System re-use.
- Phase I will likely be similar to Leaf tabletop demo, retaining Sonett brakes, hubs, and steering with modified drive shafts to adapt Leaf transaxle to Sonett hubs. Components from Leaf to include Motor, Inverter, VCM, BCM, DCJB, On-Board Charger and Charge ports, Shift Control, Power On Control, wiring harnesses (inc 12V fuses, relays), liquid cooling system, some display and control instrument / switches.
- Phase II will likely aim to fully enable regenerative braking, may incorporate Leaf braking system (master cylinder, brake controller, ABS controller, calipers, parking brake controller), hubs and wheel speed sensors (preferably in modified Sonett knuckles to avoid suspension changes), possibly adapt steering sensors and electric power steering.
- HVAC and other creature comforts (audio, door locks, Nav, Telemetrics, electric heater) will probably be incorporated throughout phase I and II as practical / convenient.
- Final phase will be to work on restoration / cosmetics once function and fitting of components are complete.

Original Post:
Well, after about 10 years of EV dreaming, I finally took the plunge :)

I've always had a soft spot for these odd-ball Saab's, ever since owning one (that I could barely keep on the road) back in the late 90s. When researching platforms for a conversion, I was rather pleased to discover that they seemed to be an excellent candidate. With a curb weight of 1800 lbs, a Cd of 0.31, and a miniscule cross sectional area (22% smaller than 1st Gen Insight), they were fun to drive with the stock ~60 hp engine while averaging 30-35mpg in a day when 10-15mpg was typical. They were also designed as racers, being proven as a great platform for performance enhancements and doing quite well in their SCCA and rally classes.

I wasn't planning to start my search in earnest for another month or two, but when this example came up for sale locally, I couldn't say no ;)
It was about the same price that I would have spent on a fair condition runner in need of complete restoration, but had already had a simple DC conversion done in the 90s and a significant amount of work had gone into restoring the frame/floorpans and mechanicals as it passed through the ownership of two different vintage Saab restoration gurus. If nothing else its a great rolling chassis to build on, with a bonus that the old conversion has been maintained and rebuilt well enough to still be used as a commuter in the mean time.

The conversion is definitely a bit of a time capsule from a bygone era ;) From what I gather it was based on a kit from either EV America and/or Solar Car Corp in FL with a custom adapter / coupler designed by Saab Quantum designer Walter Kern to the original 4sp freewheeling transmission (used clutchless). It uses a 6" GE Series Wound DC motor (looks to be the 11.6HP commutavan motor) with forced air cooling, a Curtis 1221B-7401 controller set for 300A max, and a 96V flooded lead acid pack. Looks like it was originally set up for 16s 6V batteries, but changed over to 8s 12V at some point. Have to start in 1st gear to get it rolling, then 2nd will do just about everything except freeway speeds. Haven't tried that yet ;)

It seems like its gone through several incarnations, mostly reusing the original components. Original conversion was done '92-93 by Bud Clark of J&B Imports in CA following Walter Kern's design. System was removed and significant restoration of floorpans and mechanicals was done in 2009-10 by Jack Ashcraft in OR. Motor and Controller were rebuilt by subsequent owner in 2013, and funky split 55V chargers were replaced with a Delta-Q unit in 2014. 5/8 batteries are Trojan T1275s from 2014, 3/8 are US 12VXCs from 2009 that are getting pretty weak. Still good enough to drive it 13 miles home on surface streets and come to rest at 12.2-12.3V though (vs. ~12.6 on the Trojans).

I'm planning to get those last 3 old batteries out of there, and add some instrumentation (probably cycle analyst and a modified Celllog 8S) and keep using it for my daily 15 mile RT commute while starting plans for a major update :)

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To drop the battery, I'm assuming I'll need to get some sort of jack/lift and have the Leaf up on jack stands for clearance.

A few options I've been looking at:

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Nice, good find!
Slow progress, starting to disassemble the dash and center console to expose the connections to all the various controllers. Decided to play it safe and follow the manuals instructions to disconnect all the of the airbag / per-tensioner cable connectors at the far end before removing the airbag controller in the center, which has slowed me down quite a bit. Most are a PITA to get to. The first instruction for the passenger side airbag is "remove dash" ;)

Plan is to get everything stripped down but still drivable. Then (maybe by this weekend...) drop the battery, rewire the pack, and re-install temporarily in the interior to test. Then start unplugging all the sensors/buttons/controllers that I'm not planning to use to make sure it still runs/drives as expected.

Then I can start gutting out both cars :)


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That's more like it :)

Was able to run my first "partially disassembled" test run today. With the Airbags and Airbag controller, steering wheel switches, AV Control Unit, AV Cluster switches and combination meter / upper meter all removed I was still able to start up, shift between all the gears, drive with full power and regen (monitored with LeafSpy) and charge. Still have more stuff to disconnect, but so far so good!

I may actually end up using some of this stuff, but am trying to see just how far you can go in stripping the Leaf system down and still having full drive / regen / charge functionality. Will post more details on DTCs etc in the reusing the Leaf system thread:

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The Sonnet I and II are both a fine choice for EV conversion. They have a CdA similar to a 1st gen Insight, and make an even lighter "glider" than the 1st gen Insight by a few hundred lbs. Their low frontal area gives them a noticeable advantage over other light-weight front-wheel drive cars such as the Honda CRX or Geo Metro that are commonly converted.

My biggest gripes with the Sonnets are their rarity and their use of front wheel drive, but had I come across one when I was searching for a donor chassis, I'd have grabbed it at the right price. It's a more efficient choice than my GT6, making it an ideal candidate for a "long range" conversion.

I remember browsing the EV Tradin' Post and seeing a similar conversion for sale for a similar price, but I already had a partially-completed conversion at that point.

I suspect you will get by with ~150 Wh/mile at 60 mph on flat ground with minimal wind, if you keep a very light foot. This is with no aeromods, and tires with a Crr of 0.009.

With aeromods and lots of techniques paid towards efficiency, you could reduce that to a value approaching 100 Wh/mile. The Sonnet has such a delightfully-low frontal area, which pays dividends towards reduced power consumption from air-drag, and it's drag coefficient was 20 years ahead of its time when compared to the "average" new car sold for that time.

A 24 kWh pack will open the doors to EV conversions(such as yours) getting range and straight-line performance competing with Tesla's base Model S, and well exceeding the Leaf by all performance measures from which the conversions' components were derived.

The right chassis, with good aero and low weight, is key. Less is more.

A Leaf drivetrain is of similar performance to an AC Propulsion AC100 drivetrain when run at its maximum recommended operating voltage/current. In a light-weight car, it will go like hell... Alan Cocconi's CRX loaded with roughly 1300 lbs of lead could still do 0-60 mph in roughly 7 seconds with that AC100... Your car will have a similar amount of power to, and the greater half of 1000 pounds less weight, and nearly double the usable kWh available, when compared to Cocconi's CRX.

I just hope you can do enough suspension adjustments to get the traction you will need, or alternatively, don't ever break your CV-joints. Even if you have to limit the torque to stock ICE level due to wasted traction and/or broken components(Saabs of this vintage are typically very solidly built), it will still be a very fast performer. I don't think you'll need to limit it though... which case you may have a real monster to contend with. :D
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Thanks TC, it should be an interesting combination :)

I'm hoping to keep finished weight under 2000 lbs, but we'll see how it goes. The guy who worked on the car in ~2009 said it was weighed at ~1300 lbs empty (no electric or ICE components). I'm guessing with its current 96V lead acid system its about 2200-2330 lbs. I picked up 4 550lb capacity scales off Amazon ($30 ea), so once I start tearing it down I should see where we stand.

The steering/brakes/suspension/drive shafts are definitely where I have the most uncertainty. My original plan was to just to get some custom drive shafts built up, and keep everything else stock. Possibly with some custom springs and adjustable dampers. Things are pretty up in the air on this front currently.

Knuckles / Hubs / Spring / Dampers: The stock saab setup is dual A-arm, with steering arm and calipers behind the axles. The Leaf is MacPherson struts with steering arm behind, caliper in front. Both use twisted beam rear axle.

Brakes: It looks like at a minimum the Leaf MC unit has to be brought over to enable regen. Using the Leaf pedal box would probably simplify things as well in terms of the throttle / brake position sensors. Stock saab are single piston floating Lockheed calipers in front, drums in back. Drums are hard to find, rotors only solid are avail, standard pads and shoes still avail. Leaf has dual piston floating calipers on all 4 wheels, rears seem to be common mounting with mid-2000s 350z/G35. Fronts are common with Altima I believe. Fair amount of performance rotors / pads seem to be avail.

Steering: Saab manual rack and pinion, 15.5:1, 2.7 turns L2L. Leaf electric power assist 15.7:1, 3.3 turns L2L. Steering sensor may be needed to get regen.

Wheels/Tires: Saab has oddball 5x170mm bolt pattern, very limited wheel options. Stock wheels are narrow (5") limiting tire options, stock were 155R15. Going to Leaf hubs would potentially open up a lot more wheel / tire options.

I don't know quite where to head with all that. One option might be to get the stock Sonett knuckles machined to accept the Leaf hubs, and just get the Leaf drive shafts shortened. Then perhaps get some custom brackets made to upgrade calipers (maybe just to the Leaf calipers). Same basic idea on rear axle I guess.

I'd also thought about trying to get the Leaf knuckles modified to match up to the Sonett lower A-arm and steering arm, but that sounds tricky....

Any thoughts in this realm appreciated, definitely not my area of expertise ;)

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Well, its up in the air :)

I've got 24" of clearance from the rocker panels to the floor, so hopefully the battery will clear underneath. I ended up buying the harbor freight 1000lb hydraulic lift cart (~$180 after sale price + coupon), which is ~11" compressed. The battery info I've seen is 10.4", so in theory I should have an inch or two to spare ;)

Hopefully will start dropping the battery tonight!

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Battery is out!

No major issues. HF hydraulic cart worked well, with one issue. Normally the handle folds down for storage, I modified it so it would fold out so I could position the table right in the center of the battery. Apparently having the handle not in its vertical position causes issues with the cable release handle, so I wasn't initially able to pump the table up with the handle reclined. Messing around with the cable position I was finally able to get it to go, never had any issues having it hold steady under load, just finicky to get it to pump up with the handle down.

The additional jack in the first pic was just to support the front of the battery as I released the bolts in case I misjudged the center of gravity. The cart was positioned about 3-4" to the rear from true center to account for the greater weight in the back. That seems to work out fine, there was no pressure on the jack as I dropped the battery. Used the engine hoist to lift it off the cart and slide a work table in under, so I'm ready to crack the case and start re-wiring!

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I'm looking forward to seeing what you do with the Brakes/Wheels situation. I'm working on my own 73 Sonett conversion (still in the planning stages, haven't bit the bullet on conversion materials yet).

I'm trying to keep as much stock as possible (especially dem soccer-balls), but if you find a viable upgrade to the brakes, I'd be very interested to hear it.

Also, if you go away from the stock wheels, I might be interested in the soccer-balls...
Will do. I personally like the soccer ball wheels, but I just don't see how I can get enough rubber on the road to handle 200+ ft lbs of torque with that skinny a wheel. I'm just as interested as you are to see how that part works itself out ;)

Bare in mind that the torque from an ev is delivered smoothly and you can get away with a narrower tyre given the abilities of modern tyres. I'd suggest you plan to keep the stock wheels and only try changing them if you have a problem once the car is finished and running.

Sorry londubh
Good point tw. The stock engine in these cars was only putting out 65hp / 85 ftlb though, so this is a pretty massive increase. Substantial upgrades were fairly commonly done for SCCA and autocross, but wider wheels and tires were often discussed as one of the first and most significant handling improvements.

The problem is I'm going to have to make a fundamental choice here pretty soon. When I get the drive shafts built I'm going to have to pick between the Saab and Nissan hub splines. If I stick with Saab there are almost no alternate wheel choices given the oddball 5x170 bolt pattern. Makes brake rotor choices very limited too. Of course changing to the Nissan hubs simplifies the drive shaft to really just a shortening exercise, but introduces lots of other potential complications in terms of fitting. Seems like thats probably the way to go though.

Its hard to describe just how tall and skinny the stock 155SR15 tires are by modern standards ;)

Here's a set on an MG:

The Michelin XZX's on my Sonett are in nice shape, but date coded 1993 so I'll definately have go tire shopping. Its actually getting a bit tricky to find modern tires that will fit on the narrow 4.5" wheels and clear the fiberglass fenders. There are a few options that work, the best choice seems to be 175/65R15 as discussed in this blog:

Here's an example of a Sonett setup for autocross (engine upgraded to ~150hp) with hubs changed to allow 6.5"x15" minilights with 205/50 tires squeezed in under stock fenders. Brakes are upgraded to 4 piston Wilwood Dynalite calipers using custom brackets. Custom springs are about 1" lower than stock.

Shock options are getting hard to find too, seems like best option used to be Koni gas over adjustables but at this point I think only KYB gas are really available.

At some point I probably need to just bite the bullet and call up Jack Lawrence at Motorsport Services and see what he recommends and can still get. I can already hear my wallet screaming though ;)

Here's a picture of Jack's Sonett back in the day :)

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I've always loved this shot of a Sonett being run "naked" to shed a few more pounds for the last run of the day :)

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Here I go giving you ideas that may take things off the market for me... but it looks like 99 wheels are 15x5 with a 4x114mm bolt pattern. That means if you could go to that sort of hub/brake setup, you could have one set of wheels for when you're opening it up, and have a set of Soccer balls from a 99 for more economic cruising?
Re - Tire width

Modern cars have wide tires for the looks - not performance
One of the car mags did some testing on different size tires on a VW Golf GTI way back when and found the best lap times were with 165 tires - wider tires were slower

Also the wider the tires the more critical the suspension
Old Aston Martin's used Crossply tires - upgrading them to Radials was a NO NO as the suspension angles meant you got less grip

Overall I would be surprised if the wider tires were actually faster
Tire compound - that is much more important
Point taken, Duncan!

I had seen this a while back, and while they did note an improvement from 1/2" wider wheel for the same tire size, the biggest difference in cornering grip certainly seemed to be from compound differences.

That said, as you indicated I'm assuming much of this is suspension geometry dependent. For the case of the Sonett's suspension, at least anecdotally from past autocross / SCCA driver reports, it seems like it responds well to a wider wheel/tire. This was generally noted to have more impact on cornering flatness / roll than adding a front anti-sway bar.

This is far from my area of expertise, so I do appreciate the comments very much!

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Those tests were on a skid pan
On an actual track I would not expect to get as much benefit

With the old taller narrower tires the tire itself would move more - which is probably why the autocross drivers reported an improvement

I have built my car for this type of event - but I'm not taking it very seriously!
My aims were
Low center of gravity
- most important -
and if you are electrifying you can get a seriously low center of mass

Tires to be "square" on the road at 1/2G cornering, 1/4G acceleration
(you can't get them square all of the time)

Springs to give a natural frequency of about 100cpm

With the lower C of G I find that I don't need the anti roll bars (anti sway) at all but the Subaru suspension I'm using has the mountings for them front and back so I may use something later

Several decades ago I had a mini with a 2 litre twin cam in the front
On that car I found that a single sprint on concrete would eat my front tires so
I used second hand track tires (slicks) - much cheaper! lasted longer! and lots more grip

Track tires
First owner uses for one event - maximum performance
Second owner uses for one season
Third owner (me) gets them for $10 each and uses until the canvas shows

Use your nice wheels/tires on the road and get another set of cheap wheels with slicks for the track

This does depend on class entered - because the mini had the "wrong" engine they put me in the unlimited class so tires were open slather
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Battery teardown is progressing slowly. Taking the time to label all the connections so that I'll have a better chance of getting it all back together correctly ;) Already found several inconsistencies with the service manual, but think I'm getting a handle on it. It did help once I figured out that there are two battery types (A older, and B newer as identified by the disconnect plug type) but also types 1 (older no warmer), 2 (older with warmer), 3 (newer no warmer) and 4 (newer with warmer). I have a type A/2, but there is only one drawing of the battery internal schematic in the manual which may be a type A/1. In addition to not showing any of the battery warmer wiring, the drawing shows the HV current sensor in the Bat Junction Box on the battery negative lead, while mine appears to be on the battery positive lead as verified with a multimeter. Once I figured that out everything made more sense, as I had been using the sensor location to define bat +/-.


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