Small model engines have flow restrictions ahead of the jets to reduce the pressure enough to suck the fuel into the air flow.

This allowed the use of shorter inlet plumbing which decreased turbo lag and lowered flow restriction.

Seal unit and cleaning head pose a flow restriction resulting in a pressure difference across the pig.

If the water pressure is relatively weak, flow restriction is minimal.

The exhaust ports were also modified with a higher port roof, which reduced flow restrictions.

It does suffer from other problems such as shear losses and flow restrictions.

The smaller diameters should then be sawn off, to minimise flow restriction.

Some turbo-back (and header-back) systems replace stock catalytic converters with others having less flow restriction.

The Slant-6 manifold configuration gives relatively even distribution of fuel mixture to all cylinders, and presents less flow restriction.

This flow restriction results in efficiency losses.