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Originally Posted by Silo
No, it's NOT dude... 5 psi might be harder to imagine, so lets go to 20 psi. A GT25 at 20 psi is far less "efficient" then a GT35 at the same psi. Efficient means, that on the same engine the GT25 has too spin a lot faster then the GT35 to produce 20psi of pressure causing the compressed air produced by the GT25 to be much hotter compared to that of the GT35, which in turn means that there will NOT be the same number of oxygen molecules in that chamber!
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Yes, temperature is a factor too, but I was assuming a system with an adequately sized intercooler and boost measured post-IC, which is usually is, as it is in the GTM system.
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Conclusion: If intake temps, backpressure, boost and RPM are held constant for both setups the larger turbo will make more power because volumetric efficiency has increased due to the greater flow of the larger compressor wheel at 10PSI.
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Exactly (with the exception that we're not talking about turbos or backpressure here). Volumetric efficiency of the compressor wheel. More efficient = less energy wasted = more power for the whole system. That much is very obvious. But it's not what I was talking about. I was talking about the amount of air entering through the throttle body into the combustion chamber at 5psi (at a fixed temperature). Small picture, not big picture.