A 6-71 blower is a Roots-style positive-displacement supercharger originally designed for General Motors 6-cylinder diesel engines, where "6" refers to the number of cylinders it was matched to and "71" refers to the displacement per cylinder in cubic inches — 71 cubic inches each, 426 cubic inches total.
The 6-71 designation is a sizing code from the GM Detroit Diesel engine family, not a performance rating. The blower works by trapping air between two counter-rotating lobes and pushing a fixed volume of air into the intake with each rotation — which is why Roots-type blowers deliver boost at low RPM rather than needing to spool up like a turbocharger. The 6-71 became a hot rod staple because its physical size and airflow volume suited modified V8 applications, especially when mounted visibly through a hood opening.
- The "71" in 6-71 blower designations equals 71 cubic inches of displacement per cylinder in the original GM diesel application.
- A 6-71 Roots blower displaces approximately 426 cubic inches (6 × 71) of air per revolution.
- Common 6-71 blower dimensions sit roughly 14–15 inches long and 9–10 inches wide, making it physically large on a V8 engine.
- Roots-type blowers like the 6-71 deliver boost immediately at low RPM, unlike centrifugal superchargers or turbochargers that require higher speeds to build pressure.
- Related designations follow the same naming logic: a 8-71 blower is sized for an 8-cylinder Detroit Diesel engine at 71 cubic inches per cylinder.