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Old 11-17-2003, 03:13 PM   #1
Honda530
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Default Single Turbo Vs Twin Turbo

"This is somewhat controversial but many people believe that twin turbos spool faster than a large single turbo. This is because twin turbos use two smaller turbos with less inertia than one bigger single turbo. This is somewhat true for larger engines like the bigger v6 and inline 6 cylinders. The twin turbo will be slightl better in transient response than a bigger single turbo but not a whole lot. Smaller turbos tend to be less efficient than their bigger brothers because of the scaling of their wheel to housing clearances. The bigger turbos only have slightly larger clearances between the housing and the wheels than their much smaller little brothers. This clearance causes internal leakage, which reduces efficiency of both the compressor and turbine. Since the clearances and the leakage are proportionally larger on the smaller turbos, they are less efficient, and thus laggier than you would think they should be. There have been published studies showing that a 2% gain in turbine effieceny can overcome a 25% gain in the turbos rotating inertia so even small effieciency gains can be significant. the ratio of blade thickness to wheel size does not scale up directly either. Smaller turbos often have proportionally thick blades on their wheels for their size than larger turbos; thicker blades are aerodynamiclly less efficient. Because of these issues, a big single is the only way to go, especially when teh large pulses from a 4 cylinder can be used to spool the turbo faster in a well designed system that exploits a divided turbine housing. The only time a twin turbo should be seriously considered is on v6 and v8 motors, where it packages nicely and you can use two larger turbos. On 4 cylinders twin setup is for show only."

Honda/Acura Engine Performance. HPBooks. Mike Kojima. 159
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