Not claiming to be the expert on this, but here goes...
I have had Turbo Saabs for many years. They had a knock sensor in the block that detected pre-detonation/engine knock - it is a closed loop system. On a Turbo, the higher the boost increases the effective compression ratio of the engine - so the higher the boost, the more likely it is for the engine to experience pre-detonation/knock. A higher octane gas will reduce pre-detonation and allows for a higher compression ratio to be used in an engine. When the Saab computer would detect pre-detonation with the knock sensor, it would dial back the boost, to protect the engine, which would lower the maximum horsepower of the engine. The higher the octane gas you would use, the higher the boost level you could obtain due to less engine knock/pre-detonation detected - thus more horsepower. I would bet the Bronco turbo engine works on a similar principle, which is why higher octane fuel equals more ultimate horsepower. The newer engines in the Bronco also have direct injection, which lowers pre-detonation in the engine by only supplying fuel just in time, when it is to be combusted - so the engines in the Broncos can run higher compression ratios than older Turbo cars like my Saabs. The 1.5 Bronco engine actually has both direct fuel injection and port fuel injection - I heard it is to help protect the intake valves, which run dry of fuel in a direct injection only engine.
I have had Turbo Saabs for many years. They had a knock sensor in the block that detected pre-detonation/engine knock - it is a closed loop system. On a Turbo, the higher the boost increases the effective compression ratio of the engine - so the higher the boost, the more likely it is for the engine to experience pre-detonation/knock. A higher octane gas will reduce pre-detonation and allows for a higher compression ratio to be used in an engine. When the Saab computer would detect pre-detonation with the knock sensor, it would dial back the boost, to protect the engine, which would lower the maximum horsepower of the engine. The higher the octane gas you would use, the higher the boost level you could obtain due to less engine knock/pre-detonation detected - thus more horsepower. I would bet the Bronco turbo engine works on a similar principle, which is why higher octane fuel equals more ultimate horsepower. The newer engines in the Bronco also have direct injection, which lowers pre-detonation in the engine by only supplying fuel just in time, when it is to be combusted - so the engines in the Broncos can run higher compression ratios than older Turbo cars like my Saabs. The 1.5 Bronco engine actually has both direct fuel injection and port fuel injection - I heard it is to help protect the intake valves, which run dry of fuel in a direct injection only engine.
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