Gas vs Diesel
I must not understand your question. Diesel motors do create a low pressure zone in the intake, that is how the air gets into a NA diesels. This low pressure zone just isn't as strong in a diesel because there is no choke on the intake (from a butterfly valve or a restrictor plate)
So... you are wondering why they don't have that restriction? Intake restriction causes the engine to be less efficient. Also all big rig diesels are required to have air brakes. This uses compressed air instead of vacuum assisted brake booster like small cars. The reason they use these brake styles in large trucks is so if there is a problem with the system the brakes come on, not going out.
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