I'll respond to the bolded parts since they are presumably salient.
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Car aerodynamics is a very complex area. This is particularly so because changing one area of the car is likely to impact airflow behaviour in completely different areas. It is not like altering (say) suspension, where a change in suspension spring rates won't affect the engine's air/fuel ratio.
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Like fixing the Beetle too-fast back can impede engine cooling. Like that?
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Furthermore, the impact of a specific modification is very hard to assess based only on its description.
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But - and here's the key point - no-one can say with certainty what an outcome is until the modification has been tested.
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There exists received folk wisdom. Using, again, the Beetle as an example. 145s on the front, a rake, de-burblized (No side trim, fender-top turn signals, running boards). Collectively, Cal-Look. It was hashed out 1/4 mile at a time. Pro-street gave us the doghouse boat tail.