# Help me decide on fast EV



## major (Apr 4, 2008)

foxr said:


> So it's between a 2015 500e and a 2014 spark ev. I can't for the life of me find anyone that has modified these things for performance. I mean is it that new or is every last watt already being used? For instance what would happen if you took fiat's 9:1 reduction gear and put in a 6:1? Any other thoughts input is appreciated as I've been 2 weeks without my abarth!


Hi foxr,

What's you idea of performance? Top speed? Quickest 1/4 mile? 0 to 60? Cornering? Economy? 

Likely every last Watt is not used in the OEM configuration. The designers were probably more interested in overall appeal, value, safety, reliability and corporate profit, not necessarily in that order.

With your example 9:1 change to 6:1, hard to say without knowing more technical details. Obviously acceleration would suffer. Top speed may increase as the OEM top speed is likely beyond the peak of the power curve. But the 33% ratio change may put the load curve-power curve intersection on the other side of the peak and gain nothing or even lose speed. 

The skill set needed to modify the EV is considerably different than for the ICE powered vehicle. Although network communication and programming skills will help or may be necessary in both cases.

Buy one (EV) you like and dive in.

major

{edit} http://www.nedra.com/

You might check these guys out. At least one of their members runs a Leaf and may have modded it.


----------



## Karter2 (Nov 17, 2011)

Not a production EV project, but this thread will give you some idea of what is involved ..and the potential...in modifying a stock EV motor/drive train.
In this case its a Leaf motor that the owner has more than doubled the power output just by modifying the electrical systems....no mechanical mods .
http://www.diyelectriccar.com/forums/showthread.php/1988-crx-diy-controller-and-nissan-178169.html


----------



## dcb (Dec 5, 2009)

also note that in front wheel drive mode, traction is going to be limited, which limits the usefulness of increasing the power output (plus no limited slip wheel torque sharing).


----------



## Karter2 (Nov 17, 2011)

^^^??
I can recall that being said many years ago when fwd ICE cars first started racing (Minis, Escorts, etc) and they even stated that 160 bhp would be the maximum usable limit for any fwd car.
Well, we all know how that worked out !
400+ bhp is not uncommon for fwd circuit racers, and dont even think about fwd drag strip specials !
Sure , clever diffs and traction control etc can be used, but not essential if you want the power for speed rather than max accelleration.
But , traction control is fairly common on most cars now anyway, even EVs, and i wouldnt be surprised if electronic "smart" diffs dont become available for some of these EVs.
( i think that Arlo mentioned he was going to fit a locker diff into that Leaf transaxle ? )


----------



## dcb (Dec 5, 2009)

I guess what I'm trying to say is in a production fwd car (with a fixed, muy difficult to change ratio, that is already close to the traction limit, throwing more current at it won't help it launch much harder. More volts would help it accelerate longer though, as would more current if you can use a lower ratio.

Arlo has done some amazing things with that car. If it is lighter and has a different weight distribution than a leaf it could use a different ratio for better performance (as opposed to tire smoke) though.


----------



## Karter2 (Nov 17, 2011)

I suspect Arlo is simply using his tires as a quick makeshift "dyno" for testing his controller and system mods.
It is also a good way to visually demonstrate the potential available to interested followers.


----------



## dcb (Dec 5, 2009)

but as far as buying an EV with minimal mods to make it perform better, I kinda like the spark. It has a 400 ft lb motor (bar wound no-less). they swapped the 3.17 ratio for a 3.87 in 2015, so get the lower one if you want to throw more current at it. apparently there is a "limiter" too (vid in link)? and reported at 7ish second 0-60 with room for improvement, much better than my leaf, but the leaf IS nice and roomy .

http://insideevs.com/2015-chevy-spark-ev-highlighting-changes/

but ultimately fwd is never gonna approach 1g acceleration, cuz physics. Unlike rwd, where the torque is trying to lift the entire car in the air, fwd is trying to lift the drive wheels in the air.


----------



## Karter2 (Nov 17, 2011)

dcb said:


> but ultimately fwd is never gonna approach 1g acceleration, cuz physics. Unlike rwd, where the torque is trying to lift the entire car in the air, fwd is trying to lift the drive wheels in the air.


Hmm?? ...Big call that !
Fwd cars have clocked under 1.5 secs to 60' on drag strips....which i suspect demands something greater than 1G to achieve ?
www.fwddragtimes.co.uk


----------



## foxr (Apr 16, 2015)

I ended up purchasing a 2015 fiat 500e because the spark was at least $2500 more used and It will be my semi-daily driver. Got it for $6400 with esport, gps, and sunroof. Shooting for decent 0-60 times. Already purchased konig dial in wheels(10.9 lbs) and plan on putting in lithium 12v at at 30+ pound loss as well as back seat chopped out, looking for other weighs(ways? lol) to lose some weight(in the car, I weigh 169lbs!)


----------



## dcb (Dec 5, 2009)

foxr said:


> I ended up purchasing a 2015 fiat 500e because the spark was at least $2500 more used and It will be my semi-daily driver. Got it for $6400 with esport, gps, and sunroof.


Nice bargain! fwiw, cars in this category run out of steam around 30mph, so you have your work cut out for you 
the spark is definitely a leg up though fwiw:
http://www.caranddriver.com/comparisons/final-scoring-performance-data-and-complete-specs-page-8




Karter2 said:


> Hmm?? ...Big call that !
> Fwd cars have clocked under 1.5 secs to 60' on drag strips....which i suspect demands something greater than 1G to achieve ?
> www.fwddragtimes.co.uk


shallow staging with big low pressure slicks on the front isn't your typical daily driver setup  And even then it is always going to be at an acceleration disadvantage off the line (though it can make use of downforce once you get moving).


----------



## foxr (Apr 16, 2015)

Now, I'm looking for written information about reduction gears, technical aspects, drawings anything to help me determine where the "sweet" spot actually is to improve 0-60 as Fiat has it max hp at 25mph and I have no idea why they did this. I'd like it to be between 40 and 60 mph not 25!
I.E. spark uses 3:1 fiat a 9.87:1 ....


----------



## dcb (Dec 5, 2009)

if you look at that car and driver link, the spark also makes 400 ft lbs, but peaks at ~2000 rpm, so similar performance torque wise.

400 ft lbs * 3.17 = 1268 ft lbs
147 ft lbs * 9.59 = 1409 ft lbs

and your fiat starts losing torque around 4000 rpm.

You can often put taller tires on too  your 185/55R15 are listed as 903.88 revs/mile. I think you are going to find that custom gears can be pricy.

typically you would just throw a higher voltage pack at it.

one other "trick" is to rewind/reconfigure the motor, i.e. if it is in wye, try to reconnect it in delta (and be prepared to deal with 1.73 times the current) but you will be able to hold torque to 1.73 * 4000 rpm. Or just give it a rewind with a higher kv rating (and a controller that can deliver). I'm assuming your batteries can handle the extra power too, but I've no idea.

with the higher kv rating, you can keep the pack at the same voltage, and draw more current from it, and get more rpm from the motor at the same torque. No idea what all that entails on a fiat.


----------



## foxr (Apr 16, 2015)

I thank you for your technical response on this. If you look at the graph here, it seems it doesn't really lose much power at 4k. I'm mechanically inclined but electrically declined? I can tear any vehicle apart but I'll need to invest the time to understand this as it's not a crankshaft. I prefer to do whatever is cheaper but need an understanding to obtain a proper path from beginning to end without 2 years of investigation. I've even thought about buying a drivetrain (used) just to tear into it and see what I've got to work with. Would be really nice to be able to simply reprogram what's already there and/or re-gear it like you said via tires and a possible gear.
http://www.fiat500owners.com/forum/66-fiat-500e/59290-why-our-500es-feel-so-fast-5.html


----------



## Karter2 (Nov 17, 2011)

dcb said:


> shallow staging with big low pressure slicks on the front isn't your typical daily driver setup  And even then it is always going to be at an acceleration disadvantage off the line (though it can make use of downforce once you get moving).


Sure, but the discussion wasnt about a typical daily driver,..we were refering to a max performance situation and the limitations imposed by physics...


> but ultimately fwd is never gonna approach 1g acceleration, cuz physics........


..a 7 sec qtr mile is impressive for any vehicle, ..fwd, rwd, or awd.

Foxr..... I suggest you read that thread of Arlo's again to get a feel for what can be done to improve the performance of an EV.
Unless you make some changes to increase the power output, your gains will be very limited.


----------



## dcb (Dec 5, 2009)

foxr said:


> I thank you for your technical response on this. If you look at the graph here, it seems it doesn't really lose much power at 4k.


fwiw, I said torque falls off, that is the point where it stops accelerating like a rocket, and it falls off quickly. to get to 60mph faster you have to maintain torque longer (more volts or change the rpm/volt rating of the motor and hope the battery can supply the extra current, or change the gear ratio (and hope the motor and the battery can handle the extra current needed to get the wheel torque back up). We know the motor can handle extra rpm at a lower torque already.

So keep in mind that motors are generators. And that pack voltage doesn't really change but pack current does, and motor voltage changes with rpm and current with torque (and ohms law, volts = current * resistance, power (watts) = volts * current), and basically power in = power out.

The torque is flat initially, because current is limited here by the controller. As rpm picks up the voltage generated by the motor (back emf) raises to a point where the pack voltage can no longer push the same amount of current, and torque falls off. Anyway, you got your homework cut out for you. (but always keep traction limitations in mind when doing mods if you want to actually go faster)











Karter2 said:


> Sure, but the discussion wasnt about a typical daily driver


..ahem...


foxr said:


> It will be my semi-daily driver.


Trying to focus on the OP's situation here  production street car mods/tweaks, obviously not top fuel.

7 seconds is indeed fast for any car, and very sticky tires (or a rack and pinion) will help overcome the traction limitation of street tires. I agree that 1.5 0-60 foot requires more than 1g, there is also some extra fudge with roll-out too w/slicks on front, but not enough to put it under 1g.

edit: OP, as to "why"? because off the line is the best  you can navigate city traffic w/ease with a good 0-30 time.


----------



## foxr (Apr 16, 2015)

I would prefer the spark ev drivetrain I guess but in my much better looking fiat


----------



## dcb (Dec 5, 2009)

meh, aesthetics... form follows function looks good to me


----------



## foxr (Apr 16, 2015)

From everything including the graphs it appears that if one was to change the gear ration from 9.x to 4 or 5:1 then that torque number would still flatline to 4k and then start dropping which means the acceleration felt to 30mph could continue to a high speed such as 45 or 50 mph before dropping off, does this sound correct to anyone else?


----------



## major (Apr 4, 2008)

foxr said:


> From everything including the graphs it appears that if one was to change the gear ration from 9.x to 4 or 5:1 then that torque number would still flatline to 4k and then start dropping which means the acceleration felt to 30mph could continue to a high speed such as 45 or 50 mph before dropping off, does this sound correct to anyone else?


Yeah, but it'd be half as much.


----------



## Karter2 (Nov 17, 2011)

Altering the gearing is only going to get you some different compromise between speed and accelleration.
More top speed (maybe ,but there is a limit) but with less accelleration..
..or, more accelleration with a lower top speed.
I would also suspect the Fiat/Bosch have already spent a lot of time testing different gear rarios before they settled on the one installed.
If you want more all round performance, you will have to increase the motor power/torque, which means getting involved with stirring up those invisible little electric pixies, shifting them from the battery to the motor faster !
Consider it like getting more fuel into an ICE motor by re mapping the fuel injection ( or re jetting the carb) ....but you are dealing with amps and volts instead of gas.
Really smart folk might be able to reprogramme or even modify the controller to some extent, others might just decide to change the controller/inverter to a different one.
How quick are you at learning new tech ?


----------



## Matej (Dec 4, 2015)

Beyond making the car as lightweight as possible and tinkering with suspension, tires, and wheels, there is not much else you can do for performance on a modern car.

Unless you can crack the motor control software or someone releases some kind of a standalone controller management system for the car, but that is not likely.


----------



## dcb (Dec 5, 2009)

lower the motor kv rating and fake out the current sensors (reduce the current reported by %change in kv rating) and cross fingers?

Its a long shot with an oem controller that probably has a lot of motor params in it, but would be nice if it were relatively simple and worked. Simplest possible scenario is that somehow switching motor to delta from wye is easy and you just need a voltage divider on your current sensors.


----------



## Matej (Dec 4, 2015)

Or connect an additional high performance controller to the motor and battery pack which you can activate when you want.

Use the OEM system for regular driving and switch to the secondary controller when you go racing.


----------



## dcb (Dec 5, 2009)

Matej said:


> Or connect an additional high performance controller to the motor


have you seen a 500e? where you gonna put an additional controller?


----------

