Quote:
Originally Posted by Ecky
Generally you'll see either "Premium fuel recommended" or "Premium fuel required" under the gas cap door. I understand the difference is that "recommended" are vehicles whose knock sensors will pull timing and safely operate with lower octane gas, while "required" are those that will be damaged by running regular.
Out of curiosity, is there any advantage to re-turning a vehicle where premium fuel is only recommended?
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I suspect the only difference between "premium required" and "premium recommended", is that in the latter case, the manufacturer is confident enough that their knock sensors and knock control strategy are sensitive enough that no significant damage from knock will occur if higher octane is not used. Other manufacturers might want to have the option of voiding engine warranty if low octane is used.
My user manual says that premium is required, but that 87 octane can be used on occasion if necessary. The fact of the matter is that any engine will constantly try to increase timing up to a set maximum, to learn how advanced timing can be without knock. This results in occasional knock on low octane fuels. The stock tune on this engine is very conservative with timing at high loads when poor fuel quality is detected. This pretty much ensures that the knock learning is done at lower loads where knock won't do any real damage.
Knock at low loads is said to be pretty inconsequential, but it's probably best if it's tuned out. I'm also able to run more optimal ignition timing for better power and economy. The stock knock control is so conservative at higher loads that it would result in quite a bit less power if I just ran 87 octane on the stock tune.