Lightweighting and aerodynamic optimization of a subcompact car.

So i had a real snafu on my hands with this battery that would save me 20lbs..

There was literally no fitting it in the battery tray.. at any orientation.
I had to do some fabrication but i currently live in a rented apartment and my angle grinder is loud AF and Dremel not powerful enough to cut metal.

I liked using a dremel over an angle grinder though because it's a million times more agile. I found out about the flex shaft and decided to get one, as well as the new brushless Dremel which claimed to be the most powerful of the lineup.

This new Dremel is super quiet, has more than enough torque to go through thin aluminum and steel, doesn't overheat, and the flex shaft lets me make very precise cuts in not too long of time. I totally love it!



After building a battery brace for my existing tray, i made a mistake when putting it back together. Apparently these two massive ECU connectors are designed to latch in in a particular order. I didn't use that particular order, and bent 3 of the pins on one side.

Now i know from experience that if you bend a pin too much, it will snap and now you need a new expensive part. You may be able to fix it without weakening the metal but you would need specialized tools to do that and you should be as gentle as possible.

I called a bunch of ECU repair places and nobody was willing/able to help me.
I called my local electronic stores to see if i could get a very flat and narrow needle nose pliers without a gripping surface so that i could effectively clamp them straight, and they couldn't find anything.

A new ECU from Toyota would be $1200 installed, which isn't too bad, but still sucks considering that $0.05 of metal is my problem.

I hunted around and found out that Aven 10335 was the perfect plier for the job.
Aven 10335 6" Stainless - Steel Flat Nose Pliers - ESD Safe Grip - Smooth Jaws

And also, i got a tip off the net to buy some 0.5mm mechanical pencils ( very close to the perfect diameter for the pin ) and use them for the final straightening process.Aven 10335 6" Stainless - Steel Flat Nose Pliers - ESD Safe Grip - Smooth Jaws



With some careful clamping and bending i was able to get the pins within 0.5mm of where they were stock, then i used the mechanical pencil to smooth out the pin further in a second pass, so that it didn't catch on the connector and then proceed to bend again. Tiny particles of pin came off and this tells me i'm right in doing this second pass to make the pin smooth again.







Car fired right up, no warning lights or other questionable behavior, seems like i nailed it!

Now it's time to get those lighter rims installed and see if we can actually eke out that 1-2 extra mpg.

The car build has been stalled because some idiota hit my car in the parking lot, smashing in the trunk, but luckily the damage didn't protrude too far.
Insurance says it's a total loss but i think the auto body shop quoted way too high.

I decided to take the car back, and got $10k payout for it. Got another quote afterwards for $3k to pull it back into shape. The remainder pays off a credit card!

If bodyshop dude is going to do paint work on the trunk then i'm going to have him add this spoiler i bought that comes off the Japanese hybrid model that supposedly is oriented around improving aerodynamics.

Maybe i could get him to weld some underbody aero panels on too, it never hurts to ask, lol

Lucky you if you can get a decent insurance payout and keep the car.
I'm done with ICE, but my little diesel gets 45 mpg. I await a cargo battery electric minivan, though all I see in the US is ego driven toys!

gromike said:

Lucky you if you can get a decent insurance payout and keep the car.
I'm done with ICE, but my little diesel gets 45 mpg. I await a cargo battery electric minivan, though all I see in the US is ego driven toys!

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Any '99 or earlier kei van is road legal everywhere, and they seem like they'd be (relatively) easy to convert to battery-electric. That's my plan, updated to when I actually need one.

Well, the body work is now done. $3000, and all the important structural parts were replaced, with the body panels bent back into shape and repainted. The result looks like new except for one corner of the trunk looking like it was built on a friday.

I had the body dude install the spoiler for the Japanese hybrid model that i found on ebay while he was at it.

We also swapped out those 16's for 15's. The steering feels more mushy, but ride quality has improved a bit ( a little car like this needs it ) and the butt dyno registers a minor gain. Strangely, the clutch feels better and i think that's because of the wheel weight and diameter reduction. It makes these jello stock motor mounts seem stiffer than they actually are.

The downside so far is mushier steering, but that's allright in exchange for the 1-2% power boost. It needs a lot of help in a straight lines, not in corners.



Well it's 100F out here and the car must be driven with the AC in full blast. A 12 mile trip around the suburbs resulted in 51mpg average which was quite surprising because usually i'd get in the mid-upper 40's. The car is more pleasurable to drive with the AC on thanks to all of these modifications.

This braille race battery does die after 2 weeks of not being started, but when the battery is charged, it starts better/quicker than it did new. I think the replacement for the braille battery will certainly be a lithium so i can get a better weight reduction and more battery amp hours.

More later!

They sure don't give those batteries away...

gromike said:

Lucky you if you can get a decent insurance payout and keep the car.
I'm done with ICE, but my little diesel gets 45 mpg. I await a cargo battery electric minivan, though all I see in the US is ego driven toys!

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Which diesel do you have?

neptronix said:

Well, the body work is now done. $3000, and all the important structural parts were replaced, with the body panels bent back into shape and repainted. The result looks like new except for one corner of the trunk looking like it was built on a friday.

I had the body dude install the spoiler for the Japanese hybrid model that i found on ebay while he was at it.

We also swapped out those 16's for 15's. The steering feels more mushy, but ride quality has improved a bit ( a little car like this needs it ) and the butt dyno registers a minor gain. Strangely, the clutch feels better and i think that's because of the wheel weight and diameter reduction. It makes these jello stock motor mounts seem stiffer than they actually are.

The downside so far is mushier steering, but that's allright in exchange for the 1-2% power boost. It needs a lot of help in a straight lines, not in corners.

View attachment 355254

Well it's 100F out here and the car must be driven with the AC in full blast. A 12 mile trip around the suburbs resulted in 51mpg average which was quite surprising because usually i'd get in the mid-upper 40's. The car is more pleasurable to drive with the AC on thanks to all of these modifications.

This braille race battery does die after 2 weeks of not being started, but when the battery is charged, it starts better/quicker than it did new. I think the replacement for the braille battery will certainly be a lithium so i can get a better weight reduction and more battery amp hours.

More later!

Click to expand...

51 mpg is impressive with AC running! How did you measure that?
That picture with the reflections looks like it was side swiped by a truck after coming out of the body shop lol.

Zambam said:

Which diesel do you have?

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A 1.9L tdi in a 2006 VW Golf.

gromike said:

A 1.9L tdi in a 2006 VW Golf.

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Don't the TDI's get better than 45 MPG? I had a 92 IDI Jetta Ecodiesel Turbo for many years and it got 43 to 45 MPG pretty consistently. I also had a B4 TDI wagon for a couple of years.

I've been over 50 mpg, but I gave up keeping a detailed record of its fuel consumption. 45+mpg was what it always seemed to be.

nicobie said:

They sure don't give those batteries away...

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..yeah i think the next one, i will probably make myself... sans BMS.. why not do some manual balancing here or there with an RC charger after cherry picking the cells to be matched, yanno?

Zambam said:

51 mpg is impressive with AC running! How did you measure that?
That picture with the reflections looks like it was side swiped by a truck after coming out of the body shop lol.

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Yeah the car is a Mazda and it has a realtime and average fuel economy meter built in.
I also have a Scangauge II plugged in and it reports 5-10% higher fuel economy than what i just quoted. The reason is because the Mazda fuel gauge clips at 170mpg but there's many instances where i am in neutral at high speed seeing hundreds of MPGs while the car is idling.

Typically my yearly average on the Mazda fuel meter is 45mpg or so with lots of suburban driving and very little highway miles.. i coast a lot, and it's very easy to do because the car is very aerodynamic.

neptronix said:

..yeah i think the next one, i will probably make myself... sans BMS.. why not do some manual balancing here or there with an RC charger after cherry picking the cells to be matched, yanno?

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Starter battery replacement seems like a natural use case for A123 cells.

I have a smallish school bus with a 6.5 liter GMC diesel. It hasn't gone anywhere in a long time, and I need to re-up the starting battery. If I replace with a pair of group 27 batteries like it had when I got it, I won't have any further use for the batteries once I move the bus to serve as a shed at my new place. So I want to slap together a LiFePO4 solution that would be reusable for something funner.

I was thinking these would be applicable:

4S 2P would be good for 1200 cranking amps, cost $240 plus shipping, and potentially be useful for a 24V contraption later, even if the cells don't fit into the eGo scooter I would like to revive.

Clearly they're not the lightweight champs that your hypermiler suggests (19 lbs for 74Ah), but they pack a chunk of energy compared to a conventional starting battery that weighs twice as much.

Chalo said:

Starter battery replacement seems like a natural use for A123 cells.

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No kidding, but are those no longer produced? my second favorite would be some high whrs/kg Lifepo4s ( if i can get them.. ) or LTO for it's temperature resistance.

neptronix said:

or LTO for it's temperature resistance.

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Ah, as a lifelong Texan I tend to forget that cold weather is more than a rare concern for some folks.

Oh yeah, i've seen it as low as -18f over here. more typical low is in the 20's during winter.
And then in the summer we have similar heat to Austin but it's much drier but the sun is a lot more intense due to being at 4500ft.
High desert is a tough environment!

So here are the plans going forward.

Originally i wanted to hit 70mpg and focused on highway fuel economy, but i find myself traveling on the highway very rarely.

But for the last couple of years i'm doing 35-45 along the local 'stroads' and timing lights and coasting and such..
And this is where weight matters to improve fuel economy here, not as much aerodynamics.

A big yearly money suck is running the AC at full blast; the car has a black interior and dark exterior so the duty cycle of the AC must be as high as possible. I considered painting the car ultra white, but this would be expensive. The second best bet is to use a nano ceramic tint on the windows because this provably reduces interior temperature a lot. Running the AC at a lower duty cycle could translate into some MPG gains.

As for other weight loss opportunities, i'm currently stymied, i think i picked the low hanging fruit already.

At some point i would like to turn this into a hybrid, even if a mild one. I think this is how i really improve my city/suburban fuel economy. This also improves the power of the car, which it needs with only 106 HP.

More later!

Chalo said:

Starter battery replacement seems like a natural use case for A123 cells.

I have a smallish school bus with a 6.5 liter GMC diesel. It hasn't gone anywhere in a long time, and I need to re-up the starting battery. If I replace with a pair of group 27 batteries like it had when I got it, I won't have any further use for the batteries once I move the bus to serve as a shed at my new place. So I want to slap together a LiFePO4 solution that would be reusable for something funner.

I was thinking these would be applicable:

https://batteryhookup.com/products/new-case-with-6x-3-2v-74ah-lifepo4-prismatic-cells

4S 2P would be good for 1200 cranking amps, cost $240 plus shipping, and potentially be useful for a 24V contraption later, even if the cells don't fit into the eGo scooter I would like to revive.

Clearly they're not the lightweight champs that your hypermiler suggests (19 lbs for 74Ah), but they pack a chunk of energy compared to a conventional starting battery that weighs twice as much.

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I have an '84 Bluebird All American with a Cat 3208. Dry storage it is (and solar roof), but I do need to move the thing now and then. The chassis batteries were 2 8D fla's, and while my son was home I changed it to 2 group 31 agm lead acid batteries. They work great and cost less than your LiFePO4 batteries.

gromike said:

I changed it to 2 group 31 agm lead acid batteries. They work great and cost less than your LiFePO4 batteries.

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I know I could do that and it would be a little cheaper, but after the bus is relocated, the batteries would be of no further use to me for anything. That's what makes me want to use LiFePO4 instead.

Chalo said:

I was thinking these would be applicable:

https://batteryhookup.com/products/new-case-with-6x-3-2v-74ah-lifepo4-prismatic-cells

4S 2P would be good for 1200 cranking amps, cost $240 plus shipping, and potentially be useful for a 24V contraption later, even if the cells don't fit into the eGo scooter I would like to revive.

Clearly they're not the lightweight champs that your hypermiler suggests (19 lbs for 74Ah), but they pack a chunk of energy compared to a conventional starting battery that weighs twice as much.

Click to expand...

Wow, that's a deal. I can't wait to replace the lightweight AGM when it dies with some lithium.

neptronix said:

Wow, that's a deal. I can't wait to replace the lightweight AGM when it dies with some lithium.

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I find it an incredibly lucky accident that LiFePO4 cells are such an easy retrofit for any legacy equipment designed around lead acid batteries. As long as the pack is balanced somehow, 2 LiFePO4 cells stand in perfectly for 3 lead cells in nominal 6V increments. Chargers work, voltage regulators work, everything works. There are even "starting" versions and "deep discharge" versions. So good.

I'm not afraid enough of NMC, NCA or whatever to prefer lithium iron phosphate on that basis, but being a nearly plug and play substitute for lead is an amazing boon. The correspondence between 14S lithium cobalt voltage and 16S LiFePO4 voltage is also a bonus; it's just not part of my battery ecosystem.

Yeah, non-lifepo4 would be cool for ultimate weight loss but because you have little lineup in voltages therefore you need to oversize the pack a lot or use some voltage conversion ( energy lossy and possibly quite bulky )

I think a 4S lifepo4 pack would be reasonable to balance periodically with a RC balancer. You could run the balancer off the battery too. It would take eons to balance, but if we make some effort to match the cells with a graphing discharger, the amount of balancing you'd need to do would be close to nothing.

Some modern lifepo4 we can buy is in the 130whrs/kg range which is reasonable; in theory we could hit 1/3rd the weight of a regular starter battery, and the battery could last a decade or so if a large amount of headroom was in the discharge spec.

Interesting thread. Didn't expect that here... Just please don't hypermile or puls-n-glide right in front of me in the left lane.

Some random comments/observations:
- Neptronix: I switched from a Scangauge II to the Torque app, with a standard bluetooth OBD 2 plug. It allowed me to program a few more observables (particulate filter load) for my 2012 VW TDI. There might also be some interesting stuff available for your car. But I use the phone also for navigation in the car, so it's always there.
- Gromike: If you are getting 45 mpg+ out of your TDI, you are driving it all wrong. These cars have as much torque as a GTI, and should be driven accordingly! I can make the front tires squeal in 2nd gear on takeoff, and still get 36 mpg. (Your 2006 doesn't have the double-clutch automatic, so the squealing trick might not work.)
- Neptronix: have you thought about replacing the metal hood with a lightweight composite part? You could use the existing hood as a mold for lamination, and/or cut out the center part of the existing hood, keep the mounting and latching hardware and periphery in the original metal, and just laminate the central part.
- That rear spoiler might not necessarily increase mpg; some (most? at least originally?) decrease lift or increase down force at the rear, which might decrease gas milage.
- Ditto for 'turbulators': I did a test on my TDI wagon, and it made no difference at all (within 1 or 2 % uncertainty). On a standard TDI Golf it did definitely save about 5% fuel, with high significance in the statistical analysis; I did that for somebody else's fuel milage data.
- Last not least: Even the Scangauge mpg is not 100% accurate; I'd always cross check with manual bookkeeping when refueling.

Gruesome said:

Interesting thread. Didn't expect that here... Just please don't hypermile or puls-n-glide right in front of me in the left lane.

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I'm a very respectful hypermiler, you'll find me doing 5-10mph under in the right lane of the highway creating a buffer zone for people to get in and out of offramps, lol.

Replies:
- Torque app sounds cool, i prefer a standalone unit that doesn't interface with my phone though.
- I haven't thought about the hood, but that would be a great place to shed weight and make the FWD car more balanced. I like the idea of cutting a hole in the hood and filling it in with composite but i wonder about the composite - metal interface and how that works? ( are we gluing it in place or bolting it, what? )
- IDK about the spoiler, the Japanese hybrid model is said to use it for efficiency purposes and it's shape is so similar to newer mazda3 rear ends that are more aerodynamic. I figured it couldn't hurt.
- Turbolaters sound interesting, i'll have to research them. In my experience, aerodynamic modifications have a good impact on this car.
- Scanguage accuracy: yeah i get that and tend to keep mine calibrated because the truth is the most important and the only way to continue improving.

Most people don't believe the MPG of this car, i'll post up a video sometime in the future.

Re: laminating center of hood: how do they bond bicycle metal steering heads etc. to carbon fiber frames? I'd assume it would be easiest and look best if you laminate it right in and around the metal frame, maybe with some holes drilled in the metal in the overlap area, so the laminate can connect from both sides through the holes.
Epoxy and cyanate ester resins seem to bond ok to metals in my experience; the metal just needs to be extremely clean. I guess if using carbon fiber one has to be a bit careful about thermal expansion, because carbon fiber has none. So you don't want the curing temperature too high, as the metal will shrink while cooling down after the laminate has locked in at the curing temperature.

Instead of a solid laminate, I'd consider a two-sheet sandwich with a thin hex-cell or foam filler. You gain stiffness at the same mass.

Before doing anything, it needs a careful calculation to make sure the mass savings are worth the effort.

These guys do this commercially, but maybe not for your car, unless there is a high performance version of it...