Originally Posted by fast murray
I've been told there's no benefit to running higher octane gas than what the compression ratio of your engine dictates.
I don't think that this is so true anymore. In the quest for more power out of smaller displacement engines and better fuel economy, most modern engines have very high compression ratios. Ratios this high would have absolutely required high octane fuel to prevent detonation in the old days.
In today's world of variable cam timing and variable timing advance, one can use 87 octane in high compression engines. The ECM manages all of this with detonation sensors to get maximum performance for the fuel and load conditions.
So, there CAN be some benefit to higher octane fuels in many engines. This allows more advance; giving higher performance and economy. This is especially true in turbocharged or supercharged engines.
I've monitored the timing advance on my F150 with a ScanGaugeII. I can tell you that the ECM is constantly changing the timing. And when I tow, I can definitely tell the difference between 87 and 91 octane on the truck's ability to hold 6th gear on uphills. It runs fine on 87 and doesn't detonate. But there is a performance difference when running 91.
My turbocharged VW Jetta is definitely faster with 91 and gets about 10% better fuel economy. Why? On 87 it pulls a lot of timing to prevent detonation.
2012 F150 FX4 Ecoboost, 2016 Surveyor 274BHS
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