Impact/EV-1:a forensic reconstruction
 

I thought I would post the "numbers" portion of this thread now, and see if we can reach agreement on my methodology.There are images of the car in the archives in my aerodynamics photos album.

For references,I have relied on:EV1.THE ELECTRIC CAR.copyright,General Motors,1996; CAR and DRIVER,June,1994,p.94; MVP COMMUNICATIONS INC.,Troy,Michigan' "GM ELECTRIC VEHICLE,Ft.Stockton,B-ROLL";MECHANICAL ENGINEERING,October,1999,pp 74-77.

Brief History:

http://www.avinc.com/img/engineering/ev1_bg.jpg
(Source: http://www.avinc.com/glossary/gm_impact_ev)

The EV-1 began life in 1988,as the" Impact",developed for GM by Aerovironment,Simi Valley,California,under the supervision of Dr.Paul MacCready.Impact went from a sheet of paper to a functional prototype in 18-months,and bowed at the Greater Los Angeles Auto Show in 1990.

After four permutations and assistance from Delco-Remy,Delco Electronics,GM Aero Lab,and Hughes Aircraft Co., the"raindrop" car emerged on the market in 1996,as a lease-only EV-1,handled through GM's newly-created Saturn Corp.

Constructed at the Reatta Craft Center,Lansing,Michigan,the EV-1 was to achieve compliance for Zero-Emission-Vehicles mandated by the California Air Resources Board,which would allow GM to sell the rest of it's products in California,starting 1998.

---

Mechanical specs of interest to ecomodders are:

http://img.photobucket.com/albums/v2...1/P1010198.jpg
(source: http://ecomodder.com/forum/showthrea...-56k-5598.html)

Height-1281mm ( 50.5 inches )
Width-1766mm ( 69.5 inches )
Frontal Area 1.9468 square meters ( 21.025 square feet )
Cd 0.188
Drag Factor ( CdA ) 0.366 square meters ( 3.9528 square feet )
Length 4309mm ( 169.7 inches )
Fineness Ratio 3.360:1
Power 102.2 kW ( 137-hp )
Voltage 312-VDC ( @ pack )
Tires P 175/65R 14 Michelin Proxima RR all-season radial with puncture-sealant
Curb Weight 1350 kg ( 2970 pounds )
Performance: Top Speed 129 km/h ( 80 mph )[electronically-limited].

***************************************

Land speed record & modifications

http://ecomodder.com/forum/member-ae...-duct-tape.jpg

During March 10-11,1994,the pre-production EV-1 was modified and run at the Bridgestone/Firestone Proving-Grounds,Ft.Stockton,Texas,for an attempt at the land speed record for electric cars.

The following modifications were performed for the event:

• The car's interior was gutted save for one racing seat.
• A complete roll-cage was installed.
• The car was lowered 25mm ( 1-inch )
• Windshield wipers and sideview mirrors were removed.
• The cowl area was covered by a plastic panel and duct tape
• Full-coverage wheel discs were screwed to the rims
• A "six-pack",containing extra batteries was installed in the front passenger seat location,boosting voltage to 384-VDC
• The LLR tires were replaced with Z-Rated Michelin tires.
• "Race" weight is estimated at approx. 1573-kg ( 3460-lbs )

Vehicle envelope parameters based on mods are as follows:

Due to the 222.5mm ( 8.9 inch ) differential in wheel track from the front to rear,with the 25mm lowering,the car loses 0.0143 square meters ( 22.9 square inches ) frontal area.

As mirrors do not factor into EPA frontal area,their loss difference is factored as a function of" points."The EV-1 served as the aero "mule" in the development of the GM PNGV car,and 15-points were "allowed" for the mirror delete.(I will use this value in my computations).

Using delta-Cd 0.006 for the wheelcovers ( from John Shinella's Lockheed,Marietta,GA Trans Am Pontiac research ),the modified Cd is estimated at 0.167,frontal area 1.8451 m-sq ( 19.9278 ft-sq ).

Allowing for the increased voltage,the motor power is estimated at 125.784 kW ( 168.615 hp).

Available power is estimated using Mu= 95% ( given simple gearbox and high inverter efficiency at max. load ),for 119.497 kw ( 160.18 hp ) at the drive wheels.

With this setup,the car achieved 288.3 km/h ( 178.8 mph ) top speed ( a land speed record ).

Aerodynamic power requirements at top speed are calculated at 96.871-kW ( 129.854-hp ),leaving 22.622 kW ( 30.325-hp )to overcome the resistance of the Michelin racing tires.

http://www.youtube.com/watch?v=raLY9U-BaHE

************************************************** ****

The car was subsequently returned to the garage area where the "Yellow-Ferret," 400mm ( 16-inch ) aluminum boat-tail was added,along with fresh batteries and ice for the controller.

On it's next pass,the EV-1 achieved 296.3 km/h ( 183.8 mph ) for a "new" world record.

To investigate the contribution the boat-tail made to the new record,I reverse-engineered the Cd using the new top speed.

Since the two record speeds were within 8 km/h of each other,I used the rolling resistance power from the 288.3 km/h run,and subtracting from the available 119.497 Kw,I'm left with 96.871 kW left over for aero power requirements.Using" standard-air" density for convenience,yields Cd 0.153 as the boat-tailed drag coefficient,and CdA 0.2885 m-sq ( 3.2079 ft-sq ).

++++++++++++++++++++++++++++++++++++++++++++++++++ +

So what does it all mean?

Dr.MacCready predicted that a car,like the Impact,if produced as a gasoline-powered car,would achieve upwards of 100-mpg.California Air Resources Board's Tim Yau,using a Btu yardstick,estimated that Impact would achieve 80-mpg. In 1991,GM's Ultralite,sharing a different"look",but very similar CdA was introduced to the public with 100-mpg.

http://ecomodder.com/forum/member-ae...-ultralite.jpg

GM ultralite

Had a gasoline variant of the Impact been co-developed,to share the outward architecture of the Impact/EV-1,using today's typical 48-month product cycle ( 36 for Mazda ),an 80-100 mpg vehicle could have made it to showrooms by 1993.

If the EV-1 aluminum is traded for steel,weight is added for the I.C.power-plant and drive-line,additional weight is added for fuel tank and fuel,and then the weight of the battery pack is lost,the gasoline car comes in around 1075 kg ( 2366-lbs ),within 14 kg of the Saturn SC.

As I touched on in my short post on the Impact,to spread risk,and do to corporate linkups at the time,GM could have offered the gasoline version under Buick, Cadillac, Chevrolet, Daihatsu, Geo, Holden, Isuzu, Lotus, Oldsmobile, Opel, Pontiac,Saab,Saturn,and Toyota. And as the body of the car requires no exotic technological breakthroughs,the car could have hit the market priced similar to the Saturn SC,at about $ 14,000 ( US) in 1991 dollars,and as a 4-seater.

Today,with all the R&D long paid for,a car like the gasoline EV-1 could be sold by KIA for under $8,000(US),$5,000(US) by TATA,India,and perhaps $2,500 (US) in China.

The EV1 was a nicely designed car but it was poisoned by its 1880s-tech batteries. How good would it have been with a little diesel?

Big Dave -

About 80 MPG :

Thread: EV-1:America's fastest production car
CarloSW2

how good
 

Big Dave,the car would have done even better as a diesel,as the fuel itself has about 11% more energy than gasoline,and with greater low-to-mid rpm thermal-mechanical efficiency,it has better BSFC.

At higher speeds the advantage would decline do to higher inertia of reciprocating mass required to withstand the higher compression ratios and shock-loading.You might consider the difference between today's VWs,with gasoline and TDi variants.

The lesson for the EV-1's aerodynamics,is that all cars taste better and there's less filling with a low CdA.

80-mpg
 

Looks like the numbers can stand on their own merit.Very tasty!

Don't know how I missed this thread first time around.

Phil: thanks again for posting yet more excellent info in the forum.

(I hope you don't mind I took a few minutes to tidy up the formatting of the original post.)

Can you index this under the Aerodynamic siminars?

I don't know how I missed that either. The EV1 was such a beauty in every way. Thanks Phil!

Gotta love the 'ol EV-1. Too bad GM crushed 'em. But somehow, I can understand why. One person: Rick Wagoner. He killed the EV-1. He was a big believer in the SUV industry, which explains GMs guzzling decade. Wagoner even admitted it was a big mistake to kill the EV-1, and not make a hybrid until recently. GMs biggest mistake was allowing Wagoner to become CEO. I am a big lover of GM, and a supported of their new future and the Volt program, but Wagoner made some bad moves. He is the reason most everyone here hates GM.

So, the EV1/Impact started with a Cd of .188. This drops to 0.167 with a mirror delete, short springs, and some duct tape, and 0.153 with a 16" boat tail.

That's a 11% improvement from stock to race aero, then an 8% improvement in Cd by adding the boat tail.

http://www.getmsm.com/ev/EV1/2003_0726_115526AA.JPG

Hmm.... my car has more room for improvement at the rear than an EV1 ever had. I bet about 20% of my 0.25 Cd results from the trailing wake.

http://upload.wikimedia.org/wikipedi...sight_Back.JPG

I'm just going to look at this picture and ponder for a while. Maybe I'll sit down with some cardboard and that spare rear bumper cover I bought.

How badly do I want 70mpg @ 70mph?

Robert - you just reminded me that another stat I'd like to know (estimate) about the EV1 is the physical area of the rear ("transom") of the car.

I tracked down a "rear-on" photo of it at one point to do this, but didn't follow through.

Assuming a vehicle has attached flow at the rear, this could be an interesting tidbit to compare against others.

http://www.altfuels.org/events/testd...cs/rentev1.jpg

The camera is awfully close in this photo, but based on the size of the license plate, the scale is ten pixels per inch. The transom is roughly 6.85ft². That's 34% of the EV1's 20ft² frontal area.

EDIT: I found a better photo, with specs for front and rear track drawn on it but mislabeled (track is measured from wheel center to wheel center). It suggests a transom area of 6.35ft², or 32% of frontal area.

http://ecomodder.com/forum/attachmen...1&d=1263150235

For the Insight, I have this excellent image to work with:
http://www.insightcentral.net/_images/reardims.jpg

And I find a transom of about 11.5ft², 57% of my frontal area!

Though the EV1 puts my Insight to shame, you should note that the area of the detached wake is >90% of frontal area on most cars:
http://www.the-blueprints.com/bluepr...ivic-00357.jpg

Just a couple of observations and questions.

From this layman's perspective, one of the key elements to the overall shape of the EV1 is the narrower track of the rear wheels. I don't know if the Insight has this, but it seems to be a place that the designers of today's cars don't want to go. Why not? Is it because it looks too "dorky" for the mass car buying public? Is it that much less stable?

Granted the EV1 was a 2 seater, but the layout of many of today's cars places the wheels very far forward, and very far aft. It seems that with a focus on a 4 seater instead of a 5 seater, the shape could start tapering at the B columns, the rear track could be narrowed, the wheelbase lengthened, and there would still be plenty of storage space in the resulting quasi-boattail. With all of the microprocessors in modern cars anyway, it seems that they could come up with an active suspension to counter the roll of a narrower rear track.

aerohead thanks for the great post!!!

I don't have much to add because its out of my expertise, but I sure am absorbing a lot of info and would like to thank everyone that has contributed to this post.:thumbup:

It is too bad there is not also a side view photo of the EV1.

side
 

Neil,we've found one,taken at Ft.Stockton during the speed trial.It's distorted a bit but design elements can be distinguished.
I'll get it posted ASAP unless one of the other members beats me to it.Hint-hint!

I think your forgetting something. What if you removed all the super heavy batteries and electric motors and electronics and just had a small diesel. I think it would easily be over 100 mpg probably in to the 120 - 130 mpg range. Look at what VW did. The original 1 liter concept had a cd of .159 with a 7.5 hp 300cc 1cyl N/A diesel and it managed 235 mpg. They have now changed it (for the worse) the cd is now .195 (the same as the EV1) it has a 2cyl 800cc TDI (half of a 1.6L TDI) that puts out 7 hp in eco mode and 25 hp in "Sport" mode and is a hybrid which added 201lbs to the car and it still manages 170 mpg. (Can I have the original please.)

The Insight also has inboard rear tire that are 2 inches narrower than the front.

And this does cause some instability in the snow, as the rear tires do not track in the same path as the front, making the rear end of the car jump around more than normal cars.

It does take some getting used to, and after a while you just realize it tracks straight, but moves around a bit at the same time.

Jim.

Okay,

These pictures are confusing me -- the EV-1 front and rear views are at a different scale than the plan view. And the is the Insight really that much bigger than the EV-1? The rear wheel track (center to center) is wider (1.325m) than the out to out wheel width of the EV-1 (1.24m)?

I'm trying to scale them properly, so I can measure the areas in DataCAD...

If those measurements are correct, and I've scaled the bitmaps right, then the EV-1 transom is a mere 5.308 sq ft; while the Insight transom is 1.999sq ft.
http://img.photobucket.com/albums/v7...httransoms.png
The yellow grid is 1 foot squares, and if the outline is right, then the area reported by DataCAD is very accurate. The two rear views are scaled correctly AFAICT, and the Insight looks enormous! It the EV-1 really that tiny?

binarycortex -

Very good point. That could be another option for this thread where I said EV1 + 1st Gen Honda Insight drivetrain :

http://ecomodder.com/forum/showthrea...use-12347.html

CarloSW2

Looks pretty tiny to me.

http://www.ka9q.net/ev/myev1.jpg

http://i22.photobucket.com/albums/b3...me/INSIGHT.jpg

I have the feeling that the guy with the insight is shorter than the guy with the EV1.

No, the two are very similar, IMO:

Neil, did you use the dimensions on the drawing I clipped from YouTube to establish the scale for the EV1? They appear to be correct, except that track width's label is one tire too wide. Track is correctly measured from wheel center to wheel center.

Thanks. A beautiful car indeed. Way ahead of its time aero wise. The Insight 1 is nice but not to the same standard - and I own one. Tragic that GM had no foresight.

I do have one technical question for you aero experts. In profile, the rear window looks too steep to maintain attached flow. Must be 20-25 degrees. How did they get away with that angle?

Hi Jim,

You are referring to the rear window of the EV-1? This has been the subject of other threads here at EM.

The dimentions of the EV1 don't seem right to me, grantid its been 5-6 years but the EV1 I saw on campus wasn't much higher than my belt line, Im 6'4" and it couldn't have been more than 5' wide.

Maybe a height of 42" and a width of 60"

My pickup is supposed to be 66.5" wide, the EV was definetly narrower.

Its very unfortunate that GM was unwilling to make the EV-1 body style into a steel body gasser or hybred drive, its basic shape could easily be transposed into a 3 or 4 seater just by extending the car a tad and aero would remain the same.

Imagine a metro platform with an EV-1 body, sadly KISS wore off on GM with the blasted volt mess.

I have a feeling GM underestimated the EV-1s body style appeal, I still think it is neater looking than a prius and have a feeling many others would have agreed given the opportunity.

Also remember folks, both Dodge & Ford has EV-1 like hybrids designed for the US governments paid requirement as well, both of those body styles would be worth locating for comparison.

Don't forget they both got over 75mpg with the EV-1 around 90mpg as hybrid.

Too bad big auto wouldn't produce them.

The EV1 would probably make a popular fibreglass kit.

An aero kit was the goal of the "Sunrise EV2" project: see http://ecomodder.com/forum/showthrea...again-151.html

Hi Orangeboy,

That first picture is of Phil Karn with his EV-1. I have met Phil, and that picture was taken about 3 years later. I am 5'10" my head only comes up to about his nose - back then.

BTW, that EV-1 of Phil's is the one they gave the Smithsonian...

Hello -

I just ordered a brochure from ebay that is just like this one :

GM/GENERAL MOTORS EV1 ELECTRIC Car SPEC SHEET/Brochure - eBay (item 200382445863 end time Mar-08-10 15:14:14 PST)

When it arrives, I will scan the side/front/back/top views and post them.

CarloSW2

Hello -

Here you go :

Gen II (I think another, better image is in the mail) :
http://ecomodder.com/forum/member-cf...-ev1-genii.jpg


Gen I Dimensions :
http://ecomodder.com/forum/member-cf...dimensions.jpg


Gen I Performance :
http://ecomodder.com/forum/member-cf...erformance.jpg
* - Mileage may vary based on weather, traffic, AC use, and driving style

CarloSW2

angle of rear roof slope
 

that rear window area "looks" like it is too steep and air would detach? do any of you know the angle? i know its an awsome cd car thats why im asking.

Hello -

Here are the pictures I wanted to post, but the item hadn't arrived yet :

http://ecomodder.com/forum/member-cf...-side-view.jpg

I guess that the "rear wheel" shadow means that this picture probably has some perspective in it, :o .

http://ecomodder.com/forum/member-cf...front-view.jpg

The vertical lines in the pictures are the fold-out crease.

CarloSW2

Too bad the top is a different scale than the front and back. Notice that the mirror supports are kind of "buried" in the rear view, so yes, there is a little perspective distortion.

Neil -

I totally missed that. Thanks. Back in post #20 you can see the same thing. I'll bet they came from the same source.

CarloSW2

angles
 

At 4-locations,moving back along the template,for 10,20,30,and 40% aft-body,I measured 9,20,19,and 15-degrees,respectively.
With the racing boat tail,the terminus angle is 11-degrees.
If you lay a straight-edge across the back of the boat tail and up over the backlight,it measures 16-degrees.

Also, in the low angle pictures I've seen, you can see the rear wheels from the front because the rear track was quite a bit narrower than the front.

Is it just me, or is the "Impact" (prototype of the EV-1) a much better looking car?
http://go635254.s3.amazonaws.com/gas.../Gm-impact.jpg

The nose is obviously different, and I detect a deeper contour in the doors and a slightly "hunched" rear fender -- anything else different that you can see? Was the Cd different?

Maybe it is tapered from the sides? That is, instead of looking at airflow from the side of the car, look at it from the top.