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Supercharger boost
A belt-driven supercharger gives boost directly linked to size and belt ratio. Choose the blower size, enter the displacement and drive, and you get an estimated boost.
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Estimated boost
0,67 bar
Estimated boost for a Roots blower at sea level. Real pressure depends on the condition of the rotors and temperature.
How the calculation works
A Roots blower pumps a known volume per revolution. The blower volume times the belt ratio times two, divided by the displacement, gives how much air the blower delivers compared with what the engine would draw on its own. The excess over one becomes boost. The model deducts an efficiency for internal leakage.
Overdriving the belt raises the boost but also the temperature and the load. This is an estimate at sea level for a typical Roots blower. Real boost depends on the condition of the rotors, temperature and sealing, so treat it as a starting point.
Example
A 6-71 (339 CID) on a 5,7-litre V8 with 1:1 drive gives around 0,67 bar (just under 10 psi) of boost.
Blower sizes (Roots)
| Supercharger | Volume |
|---|---|
| 6-71 small | 339 CID |
| 6-71 large | 411 CID |
| 8-71 | 436 CID |
| 10-71 | 466 CID |
| 12-71 | 495 CID |
| 14-71 | 521 CID |
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Common questions about supercharger boost
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