Spirit of EcoModder shape drag comparison
 

Had hoped to have had this pulled together long ago as well.
This list represents vehicles which share the same shape drag as Spirit,as of 2014,based upon the DARKO Technologies wind tunnel test results.
If given the same frontal area,they would be indistinguishable from one another,as far as the atmosphere is concerned.
*1927 Spirit of St. Louis, Ryan NYP fuselage
*1933 Walter Lay Model# 12
*1934 DeSoto Airflow aerodynamic test mule, minus the tail stinger
*1939 BMW 328-based,Touring Super Leggera
*1948 Tucker Torpedo
*1951 Hotchkiss Gregoire
*1952 Alfa Romeo Disco Volante concept
*1953 Panhard Dyna sedan 54
*1960 PFY concept, Prof. Alberto Morelli
*1967 Porsche 907 Longtail, Le Mans
*1969 Chrysler Dodge Charger Daytona, sans wing, @ 18-degree backlight
*1970 Citroen SM
*1975 Nissan AD-1 concept
*1977 NASA 'Shoebox' Ford Econoline van w/ edge radii & belly pan
*1979 Citroen CX
*1980 Medusa concept, ItalDesign
*1981 NASA Ford Econoline aerodynamic test mule with all-rounded edges and full belly pan
*1982 AVION, by Craig Henderson
*1986 Brabus Autosports' Mercedes-Benz W124-Series with aero kit
*1987 GM Oldsmobile AEROTECH Longtail, Ed Welburn
*1988 Dimensione Design PPG 4X4 pace car
*1989 OPEL Calibra 16-V
*1990 GM Chevrolet CERV-III mid-engine Corvette concept
*1993 FIAT Punto w/ ring vortex & fan wheels
*1994 Audi A8
*1994 Chrysler AVIAT concept
*1995 M-B E-Class
*1996 BMW 5-Series
*1996 VW Passat sedan/wagon
*2000 M-B S-Class
*2001 LEXUS LS 430
*2002 M-B E-Class
*2003 Toyota Prius
*2003 INFINITI G35 Coupe w/ aero pkg.
*2004 M-B CLS-Class
*2006 HONDA CIVIC Hybrid
*2006 LEXUS LS 460
*2006 M-B S-Class
*2006 M-B S550
*2007 BMW 320d
*2007 GM Opel Insignia- Eco Flex
*2007 M-B C-Class
*2007 Toyota Camry Hybrid
*2009 BMW E90
*2009 LEXUS HS 250h
*2009 Mazda 6i GT
*2009 NISSAN GT-R
*2010 Audi A8
*2010 Hyundai i-flow concept w/ 'Tesla' mirrors
*2010 KIA Ray concept w/ 'Tesla' mirrors
*2011 Buick Regal
*2011 Audi A6/S6 Quattro
*2011 OPEL Insignia
*2011 GM Buick Regal
*2011 GM SAAB Phoenix concept w/ 'Tesla' mirrors
*2011 Audi A8L
*2011 Audi A6 QUATTRO
*2012 KIA Optima Hybrid
*2012 BMW 3-Series
*2012 Tesla Model S
*2013 Infiniti Q50
*2013 Lexus GS
*2013 Mitsubishi CA-MiEV concept
*2013 VW Jetta Hybrid
*2014 Toyota Prius
*2014 BMW i8
*2014 Spirit of Ecomodder
*2014 Infiniti Q50
*2015 Hyundai Genesis
*2015 Jaguar XE
*2015 SCION FR-S
*2015 Subaru BR-Z
*2015 VW XL Sport concept w/ 'Tesla' mirrors
*2016 BMW i8
*2016 BMW 340
*2016 BMW 4
*2016 Chrysler 200
*2016 Hyundai Elantra
*2016 Hyundai Sonata
*2016 Mazda-6
*2016 Mitsubishi Mirage-G
*2016 Jaguar F-Type
*2016 BMW 340
*2016 Jaguar XF
*2016 Prof., Ph.D. Joseph Katz' 'generic SUV' with full boat-tail
*2016 VW Golf-VII Euro spec
*2016 VW e-Golf BEV
*2019 KIA K900
*2020 Audi e-tron Sportback
*2020 VW ID.3
*2023 Toyota bZ4X
*2023 Toyota Crown
*2023 Fisker OCEAN w/22-inch Air Glider wheels
*2023 Porsche Taycan 4 Cross Turismo
*2023 Subaru Solterra
*2023 Toyota PRIUS
With a March 1974 copy of CAR and DRIVER and some perspicacity,one could embark on 43-years of streamlining mischief!:)

The old [I]Sports Car Graphic[I] magazine gave drag in lbs calculated at 100 mph in their road tests in the 1970's. Joseph Katz also lists Cd for a number of passenger cars.

Sports Car Graphic
 

Lucky you!
CAR and DRIVER,linear descendant of SCG, refers to them every once in awhile.I've never seen a copy before.And every time I hit the swap meets,I look for them.'never know!:)

R&T
 

Yes,I was 'looking' when that one was circulating.It's a very good article and was one that fed my my interest in aero,in a world which otherwise didn't seem to really care.
And every now and then I'll run across 'books' which are compilations of Road & Track road test reviews.
And R&T remain one of the few rags which will report Cd,frontal area,CdA.Not always,but I'll settle for any table crumbs which fall my way.:)

Please provide a link to the 2014 version of your truck Phil.

All I could quickly find was this 2012 information quoted below.

http://ecomodder.com/forum/showthrea...tml#post289914
What Cd number does your opening list all match?

2014
 

All the vehicles are in the Cd 0.26-to- Cd 0.27 range. Some were provided with 'counts', most not.
The Spirit of Ecomodder thread should have the data from DARKO.
There is the possibility that, if measured at the A2 Tunnel, Spirit would have recorded Cd 0.244 with mirrors. Cd 0.219 without.
The fuel economy is better than what Cd 0.2675 average would predict, but I had rubber gearing, passenger car tires, and syn-lube. So that might help explain the higher numbers, and the higher top speed.
I'd like to go to North Carolina and check the Cd there.

Spirit of Ecomodder 2023
 

I haven't done a road trip in the truck since 2017, and have attempted to reduce my carbon footprint by driving less in the meantime.
We had a death in the family, and air travel has lost it's attraction for me, so I elected to create copious amounts of carbon-dioxide with a 2,890-mile trip to Newport Beach, California and back.
The Plex headlight covers had been destroyed by hail and were missing
Most of the belly pan was off ( All -new exhaust from CAT on back ).
No tail.
I made my way up to I-40 to get away from the heat dome a bit. I drove 70-mph in the slow lane.
40-miles east of Santa Rosa, New Mexico the diffuser was destroyed by potholes and road gators. I limped into a rest area after about 20-miles at 20-mph.
The forwards half of the diffuser was pointing 'backwards' and dragging the ground. I used the hydraulic jack to crush the forwards section up against the rearwards section, then used two motorcycle tie-down straps to secure it where it would clear the road.
I made it on to Southern California for a memorial service, then back on the road for home.
I averaged 30.11-mpg for the trip, which is okay, considering what's missing.
I have a culvert to go in soon, repairing my driveway, needed if I'm to complete the underside.
The concrete in the shop will be next, which will allow attachment of the new ( 2017 ) boat-tail.
And allow a laundry list of other work needed to get it ready for Mooresville, North Carolina.
The engine appears to be fit, at 427,000 miles. And I've got a shot at breaking into 40-mpg territory with the new kit.
As an aside, I got a look at about all extant BEVs in existence while in the Orange County area. And Tesla, Hyundai, Porsche, M-B, and KIA BEVs were doing cross-countries on the interstate.
I think an EV conversion is on the table for Spirit.

What's the solution; stiffen the plate so it won't fold , or make the forward attachment more robust? Underlap the front bumper?

'solution'
 

The solution is to stay off the interstates at low light levels. In the waning daylight, staring into the low-hanging sun, you can't discern between a black asphalt patch, the tire tread thrown from a semi, or a heavy rubber mud flap that fell off of a semi.
The diffuser was shielded behind the rear axle/differential, but it made no difference to a massive missile launched by the front tires.
Biden's $ trillion infrastructure project was too little and too late to help me.:o

Having done an EV conversion, not sure why you'd want to. Figure at least an additional 500 lbs for that battery, everything else is a push weight wise.