Question for Mach4. Is the VCB bleed so great that the pump would run constant at half or full throttle or close to it? You mentioned an average of around 8Hg. Would a reservoir help?
The Alternator mounted pump sounds great till the problem of getting oil to and draining back to the engine base has to be considered.
Is there any place that a venturi could operate. Would a minimal restriction in the intake ahead of the turbo charger be possible?

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1984 300SD turbo 126
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