From some online searches I did (since I saw this topic), in some cars where the throttle body is part of a curvy path, having the throttle plate angled may help guide the air where it needs to go.
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I don't know if we can determine the optimum throttle angle for the Fiero V6 without flow testing.
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From this article:
https://www.mdpi.com/2227-9717/11/7/1897This graph shows how the flow of a throttle changes with throttle angle:
There is not much gain from 80° to 90°.
A throttle like this could feel non-linear to the driver, where the last 10° of travel doesn't change the engine output very much (as in, a dead spot). So, with a cable throttle, you may wish to limit the travel to have a more linear-feeling throttle.
Of course, with drive-by-wire, you can hide this behaviour from the driver, as throttle plate position is independent of accelerator pedal position.
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On the White Bug, I took a guess and I grinded the throttle stop so that the throttle plate could rotate to 90°.
From the seat of the pants the engine feels okay I guess
Of course, the engine is turbo, so throttle linearity went out the window anyway...
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I don't have a very strong opinion on the topic.
