RJG Posted December 31, 2011 Report Share Posted December 31, 2011 You don't need sensors in the combustion chamber - you only need knock sensors. The software advances the timing until it detects knocking. Premium fuel allows the timing to be advanced more than regular fuel. If the rest of the system is tuned to take advantage of the advanced timing then you can get more performance. My 2012 owners manual says the 2.0 EB engine is designed to operate on 87. It doesn't mention the use of higher octane fuels which is why I figure it can't take advantage of the lower volatility of high octane with some more advance. It would be good if you are right and I am wrong. Quote Link to comment Share on other sites More sharing options...
Gimp Posted January 4, 2012 Author Report Share Posted January 4, 2012 Agree. ECU may pull timing and add fuel if necessary if charge air is hot, but doubt if it has sensors in the combustion to notice an increase in octane. Also.....since high octane fuels have additives to slow combustion under higher temps and pressures, high octane fuel has very slightly less energy BTU's. So if engine is tuned for 87, and runs well on 87, best fuel economy is with 87. Higher octane fuels are a waste of money and hurt fuel economy for an engine tuned for 87. I was curious and filled up with premium several days ago. Based on the fuel economy guage I think that I was running 1 to 2 mpg lower than with regular at similiar speeds. I just refilled with regular and calculated an average of 24 MPG from the premium. This is what I have been getting with regular, under a worse driving profile. The tank of premium was run in lighter work traffic due to the holidays (less stop and go), and clearer weather with dry roads. The summary of my unscientific observation is that premium didn't provide me with any performance improvement, it provided lower MPG, and it cost more money. I'm sticking to regular. Quote Link to comment Share on other sites More sharing options...
Chingon Posted January 6, 2012 Report Share Posted January 6, 2012 Car companies have been playing with timing/octane for years. I had a 2003 Honda Accord V6 6speed manual - basically an Acura in Honda clothes. The engineers from Honda explained that it did indeed have "octane sensors" (possibly just knock sensors), and with premium fuel you got a 10hp bump. I have no doubt this is what Ford has done 9 years later... The Accord V-6 ratings assume regular-grade fuel, and Honda will market it as a regular-fuel engine. But — pssst — it's good for another 10 hp and 10-plus lbs.-ft. on premium, acknowledges V-6 engineer Asaki. http://www.usatoday.com/money/autos/reviews/2002-08-01-accord_x.htm?AID=4992781&PID=4178165&SID=1397kzv3wmdp1 Quote Link to comment Share on other sites More sharing options...
The Outrage Posted January 7, 2012 Report Share Posted January 7, 2012 Typically, the ignition timing is retarded when detonation (knock) occurs. The higher air temperatures created by a forced induction system (such as a turbocharger) compressing the intake air will lead to an increased possibility of detonation. That is why forced induction (and higher compression) engines typically require a higher octane fuel. I'd only expect decreased occurrences of detonation, not additional horsepower with a higher octane than recommended. It is probably more accurate to say that you may not experience as much of a loss from the rated output using a higher octane under very specific conditions. With that said, if the engine's ignition mapping was tuned to work with 87 octane, I'd think the normal knock levels are within reason (modern engine tend to run lean to consume most of the injected fuel and thus decrease emissions). Quote Link to comment Share on other sites More sharing options...
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