In a compound turbocharger setup, are the two turbochargers typically identical in size?

• A. True
• B. False
• C. Not sure
• D. Unknown

Answer: (B)

Compound turbo setups are designed to broaden the boost across the engine’s RPM range by using two turbines in sequence. They are not typically identical in size because the system aims to balance quick response with strong high-end boost. The smaller turbine spools up quickly, delivering boost early and reducing lag, while the larger turbine handles the greater exhaust energy at higher RPMs to produce more boost. If both were the same size, you’d trade off one benefit for the other—either slower response when trying to deliver high boost or limited high-RPM boost when focusing on fast spool. So, different sizes are chosen to optimize both response and peak boost. (Note: in some parallel twin setups, identical sizes can occur, but that’s a different configuration from the compound/two-stage arrangement.)