Prius C: thinking of developing a "70 mpg aerodynamics kit"...
 

I am excited to be picking up my Habenero Prius c tomorrow and have been doing some thinking...

I build custom trikes and have access to a pretty good fiberglass guy and what not so just how hard (possible?) would it be to do a "package" possibly including disc style hubcaps, grill block, lower front air dam, and either a kammback or possibly even "storage enhancing boat tail"

Think 70 mpg with the air on at 65mph is a reasonable goal for the masses to achieve?
Tom

Go for it! Yours is the show car. Gauge responses. The fiberglass, though heavier, will have the quality paint finish matching quality that the masses MIGHT go for!

I look forward to hearing more about this from you in the future!

good luck!

http://www.mooncraft.jp/yuratakuya/g...prius03-04.jpg

http://www.autofiends.com/wp-content.../mooncraft.jpg

http://www.mooncraft.jp/yuratakuya/g...prius02-01.jpg

It would be cool to see someone really market them :)

I would like to say I love the idea, but I think 70 mpg is going to be a very hard goal to hit.

I generally get 55 mpg @ 60 mph with my Prius in summer. If I plug in all my data (2900 lbs, .01 Crr .26 Cd, 22.4 sq/ft) into the aero & RR calculator and tweak my engine efficiency to .283, I can get the calculator to spit out 55 mpg @ 60 mph. Now, if we substitute the Prius c numbers in with 2500 lbs, the stock Cd of .29, and 22.1 sq/ft of frontal area (keeping the .283 engine efficiency and .01 Crr) we get just above 54 mpg @ 60 mph. If we bump that up to 65 mph we've now dropped down to just over 48 mpg. So, 48 mpg is roughly where you'll start. In order to get the 45% increase in mileage to get 70 mpg, you'll need to reduce the Cd down to roughly .167! That would require a TON of work to achieve. I'm not saying its not doable, but it is going to be a lot of work.

Rear wheels skirts should be part of the kit, too I think. And the Kamm back needs to have wheel strakes as part of it, like the Mooncraft.

The tail will be a must as part of the kit if you want to try to approach 70 mpg.

One of the problems you will encounter is when you reduce the overall load, you also reduce the engines efficiency. Without lower engine RPM at the higher speeds you will not be able to maintain the load that is essential for high BSFC.

regards
Mech

Old Mechanic - fortunately in this case, the car has a CVT type of transmission. So it should automatically compensate for the reduced load by reducing RPM.

Aeromodding a CVT equipped vehicle is a 2-birds-1-stone type of deal.

That isn't nearly as much of a problem on the Prius' enigne as it is on most other engines. Almost anything off idle rpm is pretty near max BSFC.

http://ecomodder.com/wiki/images/d/d...prius_bsfc.jpg

http://ecomodder.com/forum/showthrea...tml#post215758

That'd be nice.

A quick way to test the Prius C (or any other car's) aeromod mpg gain potential is to note what the mileage improvement is when drafting, as that is the mileage improvement you could get by reducing the Cd. When drafting, the only thing that has changed is the wind load (which is the only thing being changed by aeromods) because of the reduced wind speed behind the drafted vehicle. Rolling resistance, engine/transmission rotational losses are unchanged.

I have owned two cars with CVTs. They both had a range of ratios between minimum and maximum limits (600-700% range). I'm not sure about the Toyota Hybrid Synergy Drive configuration and whether it has similar limits.
On the other hand an IVT would be capable of 120 MPH at idle speed, even 1000 MPH at idle speed. No limits to the range of ratios.

regards
Mech

Old Mechanic: I don't know the Prius well enough to say.

However, relating to basjoos' idea, a quick search turned up this:

(Edited for brevity...)

From: "Drafting" experiment... 50 mpg to 65 mpg, easy! - PriusChat Forums

kit
 

Please see the thread 'Prius to get full boat tail w/ faired trailer', #25,and #27 permalinks

I'm assuming the Prius C eCVT is similar to the other Synergy drive units. Also I note that everybody except Toyota says the "C" has an Atkinson type engine. (Toyota says intelligent VVT.) The range of equivalent ratios in the eCVT is from about 4:1 down to about 0.5:1 The gearing limits are set by MG1 maximum rpm
[final drive is 3.19:1, rolling radius about 12 in. 1500 rpm cruise at 65 mph is about 0.525:1 gearing and maximum rpm pull at 30 mph is 3.6:1 gearing]
This PDF has some info. One limit on Prius economy is that the engine doesn't run below about 1500 rpm, but assuming Atkinson like torque, at 1500 rpm the "C" engine could produce about 22 hp. According to the ecomodder MPG calculator the "C" needs about 12 hp to cruise at 60. So the engine is throttled, which lowers efficiency, but lowers output more.
I don't think that's likely without major body work.

-mort

Re: the BSFE graph in post#10

This graph may be more useful as it shows both the Gen II and Gen III for
comparison:


http://i.imgur.com/TaYbQ.jpg

FWIW, I saw a Prius c in the parking garage at work today.
Gave it a good once over. Clearly a smaller car than the Prius.
I'd guess sizewise closer to the Insight I.
Impressive FE numbers being reported at PRIUSchat.
Unfortunately too small for us.

Nonetheless, I like the idea of going after all the not-so-low
hanging fruit with aero bits. I'll be watching closely.

Sven7, those images are cool. I went looking for more info and found this:
http://www.leblogauto.com/wp-content...Prius_oeuf.jpg

On Prius Chat someone claimed that the car design you posted was for sale by Toyota in the Japanese domestic market in 2010.

So... today is tomorrow! How do you like the car? :)

Question: are you mulling this over for yourself, or as a commercial venture? (Not 100% clear).

It would seem that you could do a very slight P&G with the Prius C. Just enough to get to 22 HP on the pulse then all electric on the very slight glide. Maybe a 5 MPH speed variation, with engine off 50% of the time. This would be the secret to getting very high mileage with lower overall drag numbers.
Get them low enough to get your P&G ratios above 2 to 1 or even 3 to 1 and you will see magic numbers.

Drafting in my Insight was interesting, even with the .25 ratio. I found that I could get the same mileage at 70 MPH on the Interstate as I could on a deserted 55 MPH road running parallel to the Interstate. On one trip of 650 + miles I managed 70.2 MPG while averaging 55 MPH. In the VX on one trip I managed 68 MPG at 64 MPH and that was mostly drafting at 3 stripes in the right lane of I 64 and I 95, in the late spring of 2008.

regards
Badger

I think with the right design it is totally possible. There are more than a few people who are totally new to Prius and they are posting 60mpg tanks or at least long trips. That is impressive for a brand new car with new tires and a new driver!

Picked it up yesterday, Like it so far! Ran it 300 miles with air at 72, got 45.1 (beginning mileage was only 11!

So I guess the best way to put it is what is the best way to spend $1000 in fiberglass, and tech to be able to offer a 70mpg kit for 2k or under?

Changing mirrors to video?
Back wheel skirts?
Kamm back?
Boat tail?
Relocating the nav antenna?
Grill block?
Adding a supplemental charger for primary onboard battery?
Adding more batteries (more then 1k I know)
Reprogramming to lean on EV mode more? At more reasonable speeds? (Mine kicks of at 19mph)

Anyone want to take a stab at helping me design the kit for a part of the profits? a sweet deal on kit 1? :-)

Kamm or boat tail is going to give you the largest gain for one mod.

Add a charger for the high voltage pack isn't going to net you much at all considering your EV range is under a mile.

A plugin kit can work wonders, but yeah the cost is easily more than $1k.

I don't think I'd mess with the EV cutout speed. It most likely has to do with safety of the MGs with what speed they can spin up to.

Boat tail and 60mph governor perhaps. Wheel skirts and the rest will help but not nearly as much as the boat tail. I imagine Toyota has taken care of much of the "low hanging fruit" like the belly pan and body shape.

Maybe switch to LED DRL's and tail lights if they aren't already.

Ive been away from the "sport" for a while, have there been any good developments in video rigs to replace the 2 mirrors in a "pretty" and "public accepting" way?

kit
 

If you have a university nearby which has a business college,I would recommend you get with the dean of the department to see if grad students would do a business model for you.
For under a thousand dollars you could end up with a complete business plan with all real capitalization costs and potential market information.
Without this data you don't have an ice cube's chance in hell for success.
80% of new small enterprises fail.Many lose everything they have.And it's impossible to attract venture capital unless you can prove your business on paper.
To market a $1,000 kit will cost you many tens of thousands of dollars.And its easy to just keep adding zeros.

You need to realize that market for people( b type) who will 'visually' or "astheticlly' modify their car is much smaller thatn the market for people(a type) who want better mpg.
Also the diy market(subset of b type) is broken down into:
1. those (like most here) who will say "I can make my own'(b1)
2. those who will buy it and put it on themselves(b2)
3. those who would buy and have it put on by a shop(b3).

Next: Cant call it "70mpg kit" because the first person who drives it hard and gets 60mpg is going to sue.
In fact you need to look at the CAI aftermarket as a case study.
The manufacturers show dynos and make claims of increased performance.
But when you go to car web sites, the buyers admit to not REALLY seeing any inprovement.
THe difference though is cai is cheap, throw away money. And the product doesnot effect the outward apperance. And 'looks racy' under the hood.
Next: If the european and asian aftermarket hasnt done this, you have to really ask 'why?'
They have expensive gas. And (at least in JDM) they are willing to have oiutragous looking cars.
Next: You about to face what car manufacturers face when they design cars. The lowest common dinominator. The stupid driver.
you really think that a 'grill block' isnt like passing out a free pass to sue?

Just some food for thought.

$1,000
 

I went back and looked at Continuum Dynamics semi-trailer boat-tail doings.
The Small Business Administration along with Defense Advanced Research Projects Administration allowed an initial grant of $50,000 dollars for proof of concept,which would be followed with a secondary grant for around $350,000 for commercialization of the product.
I think you need to inflate your $1,000 cost estimate for bringing a kit to market at $2,000.

mcrews -

Hmmm. At first when I read your statement something didn't sound right. From my POV the aesthetics market is far bigger than the MPG market, at least for the non-business driving population.

After re-reading it I see your distinction. I guess I wouldn't compare "want" to "modify". I would argue that the population that is willing to modify their car for MPG is much lower than the population that is willing to modify their car for aesthetic purposes.

CarloSW2

I think there is a market out there for something similar to what you are doing.

But I'm an inventor, so I have fun making ONE of something, then wandering on to new and novel things.
Want fuel for 55 cents a gallon? Btdt.
Want to make your own ethanol at the rate of 50 gallons a day? Btdt.
want a 75 mpg car? Working on it.

The aerocivic and be improved upon. Will take some testing though.

sorry, my fault. I meant it all in the context of better mpg. the 'big set' is people who want better mpg.
Then there is a subset (much smaller) who are willing to make 'visual mods' for better mpg.
My point was that (imho) the potential buyers for a visually modified car is pretty small.
And of that subset, a lot of them are diy:
a) make it themself cheap
b) buy it and put it on themselves

So any luck with this one?

I seriously doubt. "C" aerodynamics are much worse than Toyota is saying. I have observed fuel economy of 38-39MPG in ECO mode on flat wind protected interstate (no drafting) and cruise control set at 73MPH. This is not instant consumption, calculated 1.5-2hr run. And this is ECU calculated, so the real MPG even worse.

Regular Prius gets 6-8MPG better than C in similar conditions.

I would also be interested in the result.

todayican's last post was on 06-19-2014.

What would be the ROI on a 70 MPG kit?

At $1000, it would take 58k miles at $3 a gallon (longer if gas is cheaper) for gas if it took 50MPG to 70MPG. 116k miles for the $2000 estimate. There's a reason DIY and coroplast are the most common methods of modding.

The easiest way to see if 70mpg is possible at 65 mph in a Prius C is to see what the instantaneous mpg gauge shows when you are drafting someone, since that is the car's aeromodding potential. When drafting, the only thing that has changed is the aero drag (rolling resistiance, drivetrain losses, etc, are unchanged) which is what you are reducing by aeromodding.

I do not think 70MPG is possible, but 65 should be. After observing C for a while with TorquePro I came to following conclusions:
1) C engine was optimized for higher efficiency than Gen2, and sweet spot is below 2k
2) the aerodynamics of C are worse than Toyota say. CD is definitely worse than .28

I just installed VGs to see if they show any improvement at 73mph. Grill was partly blocked, not sure what else to try. I suppose could do sides if roof shows any improvement.

What kind of mileage do you get when drafting, per basjoos' suggestion?

Have you made a full Mooncraft-style body kit?

I would not say this, but that it is highly likely that the Cd is greater than 0.28. If you can perform coastdown testing per Instructables.com, then we could find out for sure and settle this:thumbup:

The C's Cd 0.28 would match the Mitsu Mirage, and they look similar IMO

http://t1.gstatic.com/images?q=tbn:A...wIo1xEZTflJI9E
http://t2.gstatic.com/images?q=tbn:A...53X4ph71XmppJq