Lightweighting and aerodynamic optimization of a subcompact car.

[neptronix]

Bad news.
This braille race battery has rapidly died after 9 months of ownership and no abuse..
Icarus flew too close to the sun with that one.

Replacing with a wally world battery because i'd like to save up for a DIY lithium.

 

[Hillhater]

Bad news.
This braille race battery has rapidly died after 9 months of ownership and no abuse..
Icarus flew too close to the sun with that one.

Replacing with a wally world battery because i'd like to save up for a DIY lithium.

Replacement / refund under warranty ?

 

[neptronix]

Replacement / refund under warranty ?

Unlikely.
I did not use it as intended

 

[Logic11]

Solar reflective paint:
According to my reading and IIRC:
Any white paint is better than any other colour.
Even silver!
If the pigment is super white and great at reflecting IR; it's better, but not dramatically so vs a white paint of any sort.

The Winner by virtue of being a much thinner, lighter coating is Hexagonal Boron Nitride: 97.9% reflective:
World’s whitest paint now thinner than ever, ideal for vehicles

Calcium Carbonate: 95.5% reflective:
(cheapest. used in whitewash for centuries)
This white paint keeps surfaces cooler than surroundings, even under direct sunlight

Barium Sulphate: 98.1% reflective:
(thick layer required. 4.5°C below ambient temperature = cooling power of ~100W/m squared IIRC)
From the vault: Whitest, coolest paint ever made

An undercoat for any colour:
Infrared-reflecting paint can cool buildings even when it is black

The trouble is finding any paints based on these pigments, using the correct particle sizes.

Clear concise instructions on how to make the paint pigments at home, easily and cheaply.
Also how to turn it into a 'paint' of sorts, but of course the pigments could be mixed into anything, like white 2K auto paint, for a car roof.

Another(unwatched as yet):

 

[Logic11]

Aircon pump and alternator off during acceleration: (if not std in your car)
I think an adjustable vacuum switch after the throttle flap in the intake is the best way of turning off the field windings in the alternator and turning off the aircon compressor during acceleration.

ie:
The vacuum decreases when the throttle is x% open, cutting power to both.
Then the vacuum goes above your set threshold at any time the engine is in an overrun condition, switching charging on for a very mild regen type story.
And you adjust the switch so you get charging at cruise 'throttle'.

Then obviously a parallel circuit to override all that if the battery voltage is under say 12.5? volts. (also adjustable)

I NB that there are many such switches to choose from and that there may well already be one in the car one might piggyback off of.
The brake booster is plumbed into the intake after the throttle flap with a smaller diameter pipe, making it a good place to T into the vacuum.

Ideally an electric clutch on the driving pulley side: That negates the parasitic drag of the belt/s too and no fiddling around modding field winding circuitry etc. That's as close as you can get to an alternator delete, besides its weight and all the flat battery anxiety.

 

[Logic11]

Low hanging fruit. Maybe:
The MAF sensor in the intake has a screen/s ahead and/or behind it that greatly throttle the easy movement of air through the intake.
Maybe it (or they) are there because air velocity is normally greater in the center of the pipe (boundry layer) and they want a more representative, even flow over the hot wire.
If that's the case; removing the screen/s would mean a richer mixture and more? power at the expense of economy..?
I think you gain more economy than you lose by the engine not having to do extra work sucking and ending up with less charge in the cylinder too.

There's a lot of discussion online about it.
eg: https://www.e46fanatics.com/threads...reen-removal-for-hp-torque-improvement.38959/

But generally they can be removed and replaced by a circlip, so it may be easy to test and see for yourself.
If sucessful; you lose a tiny bit more weight too.

I also NB all the ridges, ribs, steps etc (near hose clamps etc) in car intakes.
Smoothing/rounding all those sharp corners to minimize turbulence will help, and another couple of grams of excess weight lost.
Even the throttle valve can be aero'd. See the ellipse thing below for optimal shape.

Sanding flap wheels are your friend here for metal. They can be shaped on a grinder to better give the shape you want in whatever you're sanding.
NB that anything below 500 grit greatly increases skin friction according to the science.

Less low hanging:
Properly designed, optimal Bell Mouths on the intake AND from the filter box into the manifold.
These things make a surprising difference! But are only really effective at full throttle if you think about it

http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf

That's based on this paper where they come to the conclusion you want a quarter ellipse shape with a slightly extended outer lip.
Mouth 2.1x the throat diameter. Ellipse with a 3 to 1 ratio. IIRC

https://www.researchgate.net/publication/310773919_DEVELOPMENT_OF_BELL_MOUTH_FOR_LOW_SPEED_AXIAL_FLOW_COMPRESSOR_TESTING_FACILITY

The Right Bellmouth

Of all the aspects of intake manifold design, the bellmouths are particularly mysterious, perhaps because most do-it-yourself builders, and even many businesses, simply do not have the technical or financial resources to conduct tests of bellmouth performance. Building a single custom intake...

performancebyie.com

These can be 3D printed, but you need to fill and sand those steps out of the print.

RAM Air:
This is even less low hanging as a RAM air scoop basically has to be the most forward thing on the car, preferably in the middle of the high pressure, stagnant air area, to get it's best mild turbo effect at speed.

Then there's water ingestion to consider and the fitting of a float valve in the bottom of the filter box.

Calculating Critical Air Scoop Speed With A Forward Facing Air Inlet

For a motorsports race car or boat, a forward-facing air inlet creates ram air above certain speeds. Find the critical air scoop speed for your engine.

www.enginelabs.com

Not so much hood scoop as the gradual (7 degrees-ish) increase in airbox volume after the scoop for static pressure recovery without turbulence.

The Straight Scoop: Exploring the Science Behind Hood Scoop Design

Back in the day, “real” race cars didn’t have hood scoops. Instead they had an array of open injector stacks poking through the hood top. Scoops were superfluous. But then, …

www.onallcylinders.com

 

[neptronix]

Thanks for the ideas buddy!

White paint - i'm actually on board with that. I'm in the high desert and the sun is intense.. if the sun is out, and it's 60F/15C.. you will need to turn the air conditioner on or crack a window. Either will negatively impact efficiency.

There's also nanoceramic tint available these days available anywhere from transparent to dark.. they are designed to inhibit incoming UV.. in this environment, it'd have a higher impact than white paint. My interior is black too.. this is probably the highest impact item!

Engine mods? i have probably one of the most efficient and well designed non-hybrid engines here.. and the ECU is locked down to hell and difficult to work with.. no tuning means are available for my car. So i just ignore this aspect because it's the highest hanging fruit.

 

[Logic11]

Thanks for the ideas buddy!

White paint - i'm actually on board with that. I'm in the high desert and the sun is intense.. if the sun is out, and it's 60F/15C.. you will need to turn the air conditioner on or crack a window. Either will negatively impact efficiency.

Hmmm... Yes and No:
The white roof will actually be acting like and air conditioner by reflecting MORE heat than is shining on it, out into cold space.
Crazy I know, but there the science is!
NB the 100 watts of aircon type cooling per square meter thing in the links somewhere.

There's also nanoceramic tint available these days available anywhere from transparent to dark.. they are designed to inhibit incoming UV.. in this environment, it'd have a higher impact than white paint. My interior is black too.. this is probably the highest impact item!

Ye; stopping the light coming in the windows is a win, so coating the windows with the RIGHT stuff works, but I NB that it's Infra Red that carries the heat. (That whole sunburn on a cloudy day because you didn't feel the heat thing...)
I think other frequencies are changed into heat within a surface though.
Here I'm too light on the science to really say anything, but how else could that Barium Sulfate paint send more light out than it gets in if it didn't do the opposite?

Black Dash 'solution':
Do try POLARIZED driving or sun glasses with white stuff (papers work) on your dashboard.
What you will find is that a white dashboard is fine IF you wear the polarized shades...

Engine mods? i have probably one of the most efficient and well designed non-hybrid engines here.. and the ECU is locked down to hell and difficult to work with.. no tuning means are available for my car. So i just ignore this aspect because it's the highest hanging fruit.

Hmmm... this isn't an ECU mod or anything that will affect it badly... except for Maybe... the screen just upstream of the MAF:

(I've removed these screens without issue, but ye; for the same airflow the hot wire sees more aiflow with the screen/s removed... That's a bad thing... unless the factory decided to run the engine lean as stock..?)

They're all more a performance mods, if you choose to drive enthusiastically
If the airflow meter pics up more airflow; the ECU auto adds more fuel.

It's just the engine is doing less work to suck in the charge when the throttle is ~wide open.
ie: Those suggestions wont mess with the computer.
IIRC you did mod your air intake some already? No ill effects?

 

[Ecky]

I would be surprised if you couldn't tune the engine. I have an ND Miata with the same engine (and probably ECU) and there are loads of options for tuning it. The problem seems to be that most tunes just add power at WOT and extend the rev range. As an amateur tuner myself, I understand why they wouldn't want to touch the part throttle parts of the map.

 

[neptronix]

I've heard of two companies who once did tuning, but they're defunct now.

The USA model motor has -8hp and doesn't seem to rev as high vs the European/Japanese version. It might be different enough that adapting things is a pain.

To be honest, i think i squeezed all of the low cost fuel economy improvements that don't lead to compromises out of this car. The next ones are expensive. Messing with the ECU is unappealing. I might just leave it as is and save for a prius/electric car!

 

[Logic11]

I've heard of two companies who once did tuning, but they're defunct now.

The USA model motor has -8hp and doesn't seem to rev as high vs the European/Japanese version. It might be different enough that adapting things is a pain.

To be honest, i think i squeezed all of the low cost fuel economy improvements that don't lead to compromises out of this car. The next ones are expensive. Messing with the ECU is unappealing. I might just leave it as is and save for a prius/electric car!

Edit:
There's nothing wrong with your approach of going after the 'low hanging fruit' neptronix.
It's damn clever and I even linked this thread on Eco-Irritation recently.
It's just wild how different folks take different routes to the same thing depending on what they enjoy doing.


If you want to see the complete other side of the coin, see pgfpro's Talon TSi Compound Turbo.
He's the kind of guy who rebuilds an engine on the weekend for fun.
He's running ULTRA lean (30:1 AFR IIRC) at a super high (unbelievable!) compression ratio, on a mixture of mostly waste acetone he gets for free and a spot of gasoline. (He's in the auto paint business)
If he gets his waste acetone incinerator license he will be in the negative $/mile!

But that's just eco mode. Power mode is a whole different story!!
So you can imagine that the ECU that most people get tuned is interesting.
Basically his build is a case study on just how far you can mod the engine side of things.

There's also talk of a Combined Heat and Power system @ home.
The efficiency of an ICE goes WAY up to over 80% at least if you can use the waste heat.
Imagine making money to heat and power your house!

My 1991 Talon TSi Compound Turbo AWD - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

I thought I would start a thread about my Talon that will be capable to run in lean burn at 30+:1 A/F ratio's. Now because the Talon never was a lean

ecomodder.com

 

[neptronix]

Not interested in investing that much time and money into an antique form of propulsion.
The less gasoline it can consume ( even at peak ), the better!

If i ever put some serious sum of money into it, it would be to turn it into a mild hybrid.
I think beyond the low hanging fruit i picked, my spare cash would be better set aside for an EV or hybrid.

 

[Logic11]

Not interested in investing that much time and money into an antique form of propulsion.
The less gasoline it can consume ( even at peak ), the better!

If i ever put some serious sum of money into it, it would be to turn it into a mild hybrid.
I think beyond the low hanging fruit i picked, my spare cash would be better set aside for an EV or hybrid.

pgfpro loves tinkering with engines and racing etc.
Others prefer tinkering with E-bikes or EVs.
Different strokes for different folks is all I was saying.

 

[JackFlorey]

Aircon pump and alternator off during acceleration: (if not std in your car)

This might improve performance but will tend to decrease fuel economy. An engine is most efficient at wide open throttle; shedding loads so a given acceleration does not need WOT will increase pumping losses and decrease efficiency.

 

[Logic11]

This might improve performance but will tend to decrease fuel economy. An engine is most efficient at wide open throttle; shedding loads so a given acceleration does not need WOT will increase pumping losses and decrease efficiency.

Yep, I've seen the arguments in that direction.
There a certain throttle opening etc at which it becomes better to switch off ancillaries.

My understanding is that a lot of cars nowadays have this all figured out and auto volt/unvolt the alternator rotor accordingly.
Which do and which don't is a very grey area, as is the question of whether the aircoin pump gets the same treatment.

There's some very interesting info out on hacking into and modding the CAN bus on modern cars, which would shed some light on whatTH is actually going on.

 

[JackFlorey]

Yep, I've seen the arguments in that direction.
There a certain throttle opening etc at which it becomes better to switch off ancillaries.

Absolutely - for power. If your 0-60 time is an important sales number, and/or your car is getting lambasted for being too slow, then doing tricks like that are a great idea (and many cars do.) That works against efficiency, though.

 

[neptronix]

This is the kind of car that needs the pedal stood on quite often, especially climbing big grades on the highway.
Right now i just manually turn the AC off when ascending, to prevent needing to drop a gear whenever i can.

I think if you'd make this feature automatic, you might wear out the AC compressor clutch faster, considering that standing on the pedal with a 1.5L engine is a common occurrence. I try to shut off my AC as infrequently as possible to minimize extra wear.

An alternator switch probably works well when combined with a huge battery. Otherwise, we're probably going through lead acid batteries quite often. Possible gains are marginal.

I like the idea of turning it into a mild hybrid, even if this is just via belt drive and we're talkin' 1HP of regen + drive power via the belt. But it's a lot of work, money, and time for a marginal benefit.

The only thing i want to revisit is the lightweight battery.. but i am still waiting for the right battery ( 200whrs/kg sodium ion sounds about right )

 

[Logic11]

This is the kind of car that needs the pedal stood on quite often, especially climbing big grades on the highway.
Right now i just manually turn the AC off when ascending, to prevent needing to drop a gear whenever i can.

I think if you'd make this feature automatic, you might wear out the AC compressor clutch faster, considering that standing on the pedal with a 1.5L engine is a common occurrence. I try to shut off my AC as infrequently as possible to minimize extra wear.

Strangely the same thought occured to me recently. I posted about it on ...er... elsewhere.
The electric clutches I have seen did not have any sort of slow engage mechanism..?
Slow engage would prevent shock loading, but do nothing increasing longevity of the clutch plates.

I'm inclined to think of the clutch as a consumable and implement an auto switch it off system of some sort.
There were aftermarket kits for this (and the alternator) years back, but they seem to have faded from the market.
Likely because such systems are now integral to newer cars..? Or easy to DIY without a kit.

An alternative is a 'Underdrive Pulley'.
(A Nuvinci or some-such that turned the ancillaries at a constant low rpm would work great! )

An alternator switch probably works well when combined with a huge battery. Otherwise, we're probably going through lead acid batteries quite often. Possible gains are marginal.

Hmmm... when you consider the load the starter puts on the battery I don't think the load from running the car for what? Less than 30 seconds? occasionally is cause for concern.
Especially as any such system would/must have an override for when the battery is too flat.

There are a couple of people who have experimented with or done alternator deletes!
They manage to get 30 mile trips done IIRC.

I like the idea of turning it into a mild hybrid, even if this is just via belt drive and we're talkin' 1HP of regen + drive power via the belt. But it's a lot of work, money, and time for a marginal benefit.

I was thinking; an easy way to do that without messing with a car's electronics, is with a torque sensor/s on the driveshaft/s.
That could be connected to a bog std E-bike ctlr where you dial in the amount of pedal assist you want.

 

[classicalgas]

..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?



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.

I've been happy with Shorei motorsports lithium batteries in my Miatas ...twenty pounds lighter than the already small AGM that's spec'd. I just bought the biggest one my local motorcycle shop had (intended for a 1100cc bike, the miata is 1800 cc ) and starts easily, even at 11F. Bigger ones than this are available.

I bought a solar trickle charger that I keep on the dash( plugged into the cigarette lighter) that seems to fix the vampire loads that drain the battery if I don't drive it for a few weeks or months.

One of the Shoreis died, after seven years of use. I think it got unplugged from the shorei dedicated battery minder, after I put it under a cover and couldn't use the solar trickle charger.

 

[neptronix]

Hmm, my car comes with a 60ah battery and the braille that died so quick was a 20AH.
No solar charger, but we also don't have consistent sun.

My car has above average phantom draw. This is the kind of battery you'd fit to a v6 car, not a 4 cylinder 1.5L.

Looks like Shorai's biggest battery is only 15ah. I'm thinking that's too small for this car.
LFM36L3-BS12

 

[neptronix]

Looked around to see if the prices have improved for these batteries.

40ah, $369, 1100 cold cranking amps ( double of my stock battery ), and 15lbs ( the braille battery was about 20lbs )
Buy Ionic Lithium Car Battery | 12V, Heated, 1400 CA

Nice weight for the capacity!
Glad i waited for prices to drop... when i first bought the braille, everything for a car was north of $1000!

For next year once the existing lead acid is spent... maybe prices will be lower then, ha!

 

[classicalgas]

Hmm, my car comes with a 60ah battery and the braille that died so quick was a 20AH.
No solar charger, but we also don't have consistent sun.

My car has above average phantom draw. This is the kind of battery you'd fit to a v6 car, not a 4 cylinder 1.5L.

Looks like Shorai's biggest battery is only 15ah. I'm thinking that's too small for this car.
LFM36L3-BS12

From what I've read, comparing CCA between a lithium and AGM lead acid is not a useful comparison. I don't exactly understand why, except that lithium under real world conditions works better than the CCA would make you expect That's certainly been my experience with these two, they act like batteries 50% bigger. The only trick I used (and only in sub 15F weather) was to turn on the headlights and heater fan for ten seconds ( to warm battery with load ) turn them off, turn the ignition on for another five seconds (to build fuel pressure) and then crank the car.

The Miata forums seem to say the same things, and dis the early lithium starter batteries compared to the newer generation (mine has a full BMS in it, the early Antigravity and Brailes didn't (as I understand) The shorai battery has a multi pin port that lets it talk to the battery BMS directly (presumably to test and balance the cells individually)

My solar trickle charger lights its charge light even under heavy overcast, or tree shade, I don't think they need a lot of light.

 

[neptronix]

I think that cold temperatures affect lead acid a bit worse than lithium.

Interesting that this battery warmup trick works so well that you managed to start a car with a 12ah or smaller lithium battery!
Okay, solar charger sounds like it's workable.. what kind of wattage is yours? I'm thinking 15W is enough for my high drain car.

 

[classicalgas]

I think that cold temperatures affect lead acid a bit worse than lithium.

Interesting that this battery warmup trick works so well that you managed to start a car with a 12ah or smaller lithium battery!
Okay, solar charger sounds like it's workable.. what kind of wattage is yours? I'm thinking 15W is enough for my high drain car.

The pv trickle charger I'm using looks like this one from Ebay...https://www.ebay.com/itm/364524143921?_skw=solar+trickle+charger+for+car&itmmeta=01JQ7D4GC5QH6DR2P3KK180V25&hash=item54df550531:g:2tQAAOSwcSVlg9Hf&itmprp=enc%3AAQAKAAAA4FkggFvd1GGDu0w3yXCmi1ccAK%2BMUC4BpdDQ79R7eMmI99R29elky18UYLtvpxSKPrP7T9gqbGF9d6VE2GEcx9Cdo0chZ8fBpBniCJVvDlZdN6TmGPHkBDDBUu6Zw7SY%2Bxf7AR5gZZUHRY2XMJB1GjpA9iM2G1kNq6dwQy9U2kPCbpA4tEA7PeeqRCEZm%2BT7X1T6zJeI5IpMRpv%2FKTuDyzprathkVrQbUG%2Fyb%2Fl4ZnbjucuUhyPCjMBHIZkikSyyLs2kzRNNGvsOG6TPWTvH2vlEhnIZ66T3nrt%2F%2Bb8NAqr0%7Ctkp%3ABk9SR6CGku25ZQ

Mine looks most like the 1.8 w one, but not exactly. Going bigger shouldn't hurt anything, other than a your wallet.

I got mine in a package of two from Costco, years ago.

 

[neptronix]

Wow, only 1.8w, and that worked for you..
How old is your miata? i'm imagining a 1990's-2000's model that didn't have a ton of electronics sapping at the battery all the time.

I see that i can get up to a 20w dashboard solar charger. Possibly this could make a 30ah battery work.