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Old 03-30-2012, 10:24 AM   #27 (permalink)
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Originally Posted by euromodder View Post
The roofline drops on most cars these days - even on my boxy Volvo V50 - though not always as much as on the A2.

The box cavity should be an easy mod on a square-backed wagon though.
It won't be as efficient without a bellypan though.
Roofline indeed drops on many new cars and as air has no idea of knowing if car is wagon or not, then it might be misleading thinking that all wagons should have diffuser at 0 degrees, if roof drops, then it is not wagon in sense of aerodynamics and I think that one must pick more appropriate form from this image Sven posted to other thread:

Most of such examples were made at time when wagons were truly boxed shape, so that is why wagon is shown to have 0 degrees at optimal diffuser angle, but it might mislead modder to think that all wagons should have that as new stuff indeed has angle, so it can't be true anymore with all wagons.

So when one puts on boxed cavity to rear, one need to put diffuser, that is closer to 0 degrees, but without boxed cavity diffuser must be more angled if roofline drops, when roofline does not drop 0 degrees is best, how about boxed cavity on boxed rear end without dropping roofline? I guess 0 degrees still?

This leads to thinking that boxed cavity turns dropping roofline to be more towards boxed shape, but as it makes it smaller boxed shape it will be improvement to efficiency.

Or something like that. Most important to know would be just that there are no absolutes and it is impossible to generalize, every situation must be examined separately, but understanding why some forms require certain angle is helpful to make right judgement of what angle is going to work or which things will never work.

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