| air/fuel mixture that has higher temperature. Adiabatic compression: as you compress a gas, you also increase its temperature - the more you compress it, the greater the thermal increase in the gas. The non-turbo engine is at 10.5:1 compression ratio (as compared to 8.5:1 of the TT engine) and at TDC, the temperature of the gases in the non-turbo engine are considerably higher. This leads to detonation and is the #1 reason you cannot boost a high compression engine as high as you could with an identical engine only with lower static compression. Ignition timing has a lot to do with whether you will experience detonation, however, there is a point of diminishing returns where you have to retard the timing so much that it begins to hurt torque production. Several years ago a worker of Z1 Motorsports put together a Z32 with the NA engine and all of the twinturbo external parts. The car made 300RWHP at 8psi of boost on pumpfuel (and ignition timing was VERY retarded at 14 degrees BTDC vs. the ~24 degrees you can run on the twinturbo engine at this boost level on pumpfuel). The higher compression also notably hurt spoolup response of the turbochargers. This is due to the fact that the higher compression engine will convert more of the thermal/pressure energy into mechanical force on the piston and less of that energy is available out the exhaust port to get the turbos wound up. On the other side of the coin, a low compression engine will spool the turbos up notably quicker than the same engine with higher compression. This can be seen in a few TT's that have been built: Joel Grannas's Sport-600 powered TT and my own personal Z32 - both of which are at about 8.0:1 compression. The short answer to your question: the higher compression engine WILL detonate at lower boost pressures in comparison to an identical engine of lower compression with the same fuel type.
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