EDIT: I will add this photo from my dust test last summer:
Ridiculous how similar the shape of our cars are. In this shot you can see that without the rear spoiler, dust settled heavily on my bumper cover. When I added the decklid spoiler mockup, this was the result.
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California98Civic your trunk lid flat spoiler mock-up is clearly reducing the wake size as the "dead water zone" of little air movement is diminished thus allowing less dust deposition on the bumper cover. The "flat spoiler" seems to move away further rear the "dead water zone". Also, some air probably coming from under the car is moving up along the bumper cover.
The flat spoiler seems like a good modification. Fuel economy figures or "throttle stop" speed increase figures would be informative and very interesting if coming from your next flat spoiler trial.
I look forward to see your modifications.
Regards
__________________
Acel
See many mods in detail with results on
my modification thread for my 1999 Acura EL, similar to US Civic EX
Facts, please, give me the facts! Theoretical knowledge is verified by empirical knowledge! Check Einstein's General Relativity Theory E=MC^2! Every few years some new astrophysics observation and data prove some of Einstein's theory predictions more than a century old.