[aerohead]

Originally Posted by gumby79

What were the mpg improvements @20-21%drag reductions??
This is why I am asking for help in finding "facts"about what actually happened to improve FE from 18.237us mpg average up to 23.067 average a 26.458% increase. The only time I've had the cap off in the last 10,000mi I had a load on or severe weather
I anxiously awaiting the specifications for small diesels. As I would like to be able to publish reliable statistics.

Source for 2:1
Secrets of Better Fuel Economy
The Physics of MPG
pg 4 ph2
https://www.google.com/url?sa=t&sour...D_FWTQjBg3_j1A

Thire is a 2:1 drag(drag = Cda correction may be necessary ) to mpg on over the road diesels semi

I will take this as a compliment that my design is slightly above average especially for a blind shot in the dark with a 18 year old(as in 1998) idea from high school. Thankyou Aerohead.
A 26.458% gain on FE at any raito evan 1:1 is well above 20-21%cda avrage gain ,for a cap.
My last 3 trips to Helena Montana from Anaconda,Mt 200 mi roundtrip over 2 passes Have averaged 25.095mpg. 1 ea. 60mph (27.705mpg) 65mph(24.27) and 70mph(23.11) . With 1200lbs in tools in back under cap (the reason i haven't completed a Terminal Velocity Test the junk in my trunk will yield an invalid test )


Agreed gas vs diesel

the cost down( terminal velocity test is what i meant) was in reference to me wanting to do more testing. Mpg alone has been and will always be an unbelievable test hear@ ecomodder and in reality/life .
I am aware that a terminal velocity test will not give me the stock cda. However terminal velocity aba test ,I believe and correct me if I'm wrong, give the % improvement. And will not involve the motor in neutral.
This is my proposed test site
https://goo.gl/maps/ufJoDps6hcN2

stock sealed injection pump
a 16sq cm housing
Exhaust manafuld and turbocharger wrap
End of list
Full list of mods to motor
GraysGarage has showed that he has the necessary equipment to print the correct1:10 modle. Reference. Watch "Automotive Aerodynamics Ep. 7: Spoilers and Gurney Flaps for Racing" on YouTube
https://youtu.be/vzMe1e9fE50
This with the 1:43 model and some basic measurement angle of body ground clearance and I'm shure a couple more. Should be able to gert some reliable specifications. Thank you as your input is helpful

*At the time Texas Tech did their research,the metric they were using was that a 2% drag reduction would relate to a 1% hwy mpg improvement (not EPA HWY,just constant-speed 55-mph cruising on a straight,level,dry,windless stretch of highway after a full warm up.Based upon that,the 20-21% delta Cd would mean about a 10% mpg improvement.And they are assuming a constant BSFC for the engine.
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*As to the coasting,the Society of Automotive Engineers does not recognize 'coasting' as a reliable means to ascertain drag information.
*They do allow 'coastdown' testing which requires rigorous data acquisition/accounting and very precise measurements for validity on a road course which also satisfies rigid specifications.
*Also,top speed remains an avenue for which to reverse-engineer drag coefficients based upon 'new' top speeds attained after streamlining.I've attempted top speeds twice at Bonneville,however it was a bust,as it created more questions than answers.I wouldn't recommend top speed testing for any U.S.-spec car,since their 'top speeds' aren't really their actual top speeds unless great expense is paid to modify the power train to enable them to actually reach their top speed potential first before beginning any modifications.Euro-spec cars would be a different story.