# getting lowest WH/mile from a roadster



## valerun (Nov 12, 2010)

Hey Guys, 

so the client calls up and [basically] says: "I want you guys to build a Tesla out of my BMW Z 3". Well, maybe just letting up a bit on a 0-60. I think he would be ok with 5-6 sec. Other parameters pretty much same: 180 - 200 mile range (city / freeway mixed cycle), AC system. Money no object.

My question to you guys is: with all the tricks (LRR tires, lowering, AC system, regen), what is the lowest possible WH/mile one can reasonably get from this type of a car?

V


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## piotrsko (Dec 9, 2007)

valerun said:


> My question to you guys is: with all the tricks (LRR tires, lowering, AC system, regen), what is the lowest possible WH/mile one can reasonably get from this type of a car?
> 
> V



At what speed?


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## EVfun (Mar 14, 2010)

valerun said:


> so the client calls up and [basically] says: "I want you guys to build a Tesla out of my BMW Z 3".


So I'd tell him to basically go out and buy a Tesla -- it would be cheaper. I'f he is still up for it... well... damn near anything can be done with enough money.


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## valerun (Nov 12, 2010)

piotrsko said:


> At what speed?


"normal driving". I guess that means 20-30% in city, 70-80% freeway.


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## valerun (Nov 12, 2010)

EVfun said:


> So I'd tell him to basically go out and buy a Tesla -- it would be cheaper.


Yeah, only he has a Tesla already LOL ;-)



EVfun said:


> I'f he is still up for it... well... damn near anything can be done with enough money.


even 200 miles in a Z3? that car is small and heavier than Lotus Elise (Tesla's donor)... Even if we use the highest energy density batteries, AC, and LRRs, it still will be near-impossible... Any other tricks?


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## piotrsko (Dec 9, 2007)

I am guessing that you are now having to learn all about aerodynamics and fluids.

and I don't see weight an issue except for city driving with its attendant stop start issues.


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## drgrieve (Apr 14, 2011)

The Z3 is pretty poor for cd (.37) but has a small frontal area which helps. 

Not sure how much blocking the grill and putting in a body pan would help. You could run some aero tests with ICE using some temporary mods to see if it helps (the 60 miles to 50 miles timing test). This would also tell you your WH/mile.

Perhaps look into getting a carbon fibre hood and a hard top also.

How much heavier than stock does the client want to go - that is an important question.


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## tomofreno (Mar 3, 2009)

It will require both high energy and high power cells, former for range latter for 0 to 60 in < 6 seconds. So maybe some lithium polymer cells such as Kokam. I would start by taking some careful measurements and seeing how many kWh of cells can be fit in the car. Then based on mass and Cd*A product relative to a Tesla, estimate possible range with the size pack you can fit. Cycle life of the Kokams is probably less than LiFePO4 cells, but sounds like he can afford to replace the pack more often. I think the "tricks" like closing off the grill will be relatively small effects.


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## valerun (Nov 12, 2010)

sounds like the name of the game is higher energy density here. With a 200-mile pack, any lithium battery (even prismatic LiFePo4) will give enough power for 0-60 in <6 sec...

So what are the highest energy density cells? Also, volumetric energy density (Wh/Liter) matters just as much as mass energy density (Wh/kg) for a small car like this. 

Piotr - you were cryptic about aero and fluid dynamics. Did you have any specific ideas in mind? Would love to hear.

V


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## dtbaker (Jan 5, 2008)

one of the biggest bang for the buck I've seen on eccomodder forums is rear-wheel skirt. smaller ones include:

- smooth front hubcaps
- closing front grill
- bellypan
- remove side mirrors (go with video and plead ignorance if stopped)

a more unusual mod might be a custom softop that runs back to the trunk lid, altering the profile to more of a LeMans style coupe which usually puts the turbulence behind the car.... common body alteration in the 60's before they even used wind tunnels.


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## Bowser330 (Jun 15, 2008)

+1 on Lipo, the kokams are pretty lightweight and consume less space.

Check this out...
http://www.superlatticeinc.com/hedcell.html
http://www.superlatticeinc.com/downloads/SLPB53460330.pdf (70AH cell data)

3.7V Nom
4.2V Charged V
70AH (5C Burst = 350A)
1.7kg
363$ ea.

81 in series = 300V Nom (340V Charged V) (Can use Soliton-1)
3 in parallel = 70AH * 3 = 210AH * 5C = 1050A Burst

243 batteries = 88K$ USD, 909lbs. , 63kwh


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## valerun (Nov 12, 2010)

Bowser330 said:


> +1 on Lipo, the kokams are pretty lightweight and consume less space.
> 
> Check this out...
> 
> 243 batteries = 88K$ USD, 909lbs. , 63kwh


Thanks Bowser - these ARE sweet cells. Being LiPo, however, they got to be at least a bit touchy, no?


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## piotrsko (Dec 9, 2007)

wasn't being cryptic. It has been my experience that the fluids guys are better at drag reduction than the flyboys, possibly because their medium is more viscous with strange boundary layer characteristics. 

I saw one of these vehicles in a Walmart parking lot (go figure). Not a lot of space for large and bulky batteries. Also looks like they could use a belly pan, and some spoilers [flow diverters] front, sides, and back to clean it up for + 50 mph driving. Can you convince your client to go with a station wagon perhaps?


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## Bowser330 (Jun 15, 2008)

valerun said:


> Thanks Bowser - these ARE sweet cells. Being LiPo, however, they got to be at least a bit touchy, no?


Im no expert, but from what I heard, yes, there is more risk than using lifepo4 batteries...

http://currentevtech.com/Lithium-Batteries/Thundersky/Thundersky-160ah-cell-p26.html

3.2V (3.6V charged) = 94 batteries in series, charged = 340V, nom = 300V
160AH ea., 12.35 lbs ea. 200$ ea.

94 in series 1 in parallel = 1,161lbs, 48kwh, $18,800


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## steven4601 (Nov 11, 2010)

Have you seen Tim Catelier's Z3? He's got as much batteries in it as possible without taking extreme measures. 

evz3.blogspot.com

The space for the old gas tank can also be used for some batteries, but it will require you to remove the subframe. (I also removed the z3 subframe just to get the old fuel tank out)


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## valerun (Nov 12, 2010)

Bowser330 said:


> Im no expert, but from what I heard, yes, there is more risk than using lifepo4 batteries...
> 
> http://currentevtech.com/Lithium-Batteries/Thundersky/Thundersky-160ah-cell-p26.html
> 
> ...


Bowser - thanks. Although we are a CALB shop (for now, anyway) - having tested both of these and also learning from Jack Rickard. You can have those at $1.25 per AH, as well.

I just heard from Jack re Sinopoly battery (former TS) - they supposedly are going for $1/AH pricing above 10000AH (this is one high-performance conversion so easily within reach for many of us). Anyone has any ideas how to actually buy those?

V


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## EVfun (Mar 14, 2010)

I looked at the Sinopoly web site and found the new 60 amp hour cell listed. It still appeared to have about 2.5 to 3 milliohms of internal resistance. I'm running 60 amp hour Winston cells (early 2010 Thundersky, pre-split with the Yttrium formula) and they have about 1.3 to 1.5 milliohms of internal resistance. That is a lot better for getting amps out. I can hit them for 300 amps and they stay above 2.9 volts. The Sinopoly show 60 amps puts them under 3.0 volts for much of the discharge cycle. To much sag in my opinion, I would stick with Winston or CALB cells at this time.


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