As per the title.

Why does a turbocharged car only produce significant boost whilst the engine is under load? Is is something to do with how much exhaust is being produced or is there some kind of valve mechanism that controls this?

i.e. running the engine at 3000 RPM in neutral would not produce as much boost as the engine running at 3000 RPM whilst pulling the car uphill in gear.

Why does a turbocharged car only produce significant boost whilst the engine is under load? Is is something to do with how much exhaust is being produced or is there some kind of valve mechanism that controls this?

i.e. running the engine at 3000 RPM in neutral would not produce as much boost as the engine running at 3000 RPM whilst pulling the car uphill in gear.

As per the Title.

Why does a turbocharged car only produce significant boost whilst the engine is under load. Is is something to do with how much exhaust is being produced or is there some kind of valve mechanism that controls this ??

i.e. running the engine at 3000rpm stood still would not produce as much boost as the engine running at 3000rpm whilst pulling the car uphill in gear.

As per the title.

Why does a turbocharged car only produce significant boost whilst the engine is under load? Is is something to do with how much exhaust is being produced or is there some kind of valve mechanism that controls this?

i.e. running the engine at 3000 RPM in neutral would not produce as much boost as the engine running at 3000 RPM whilst pulling the car uphill in gear.