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Old 01-30-2013, 06:10 PM   #42
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Originally Posted by frinesi2 View Post
the 2.0l gdi ti-vct is tuned to adjust for whatever octane rating of fuel you've put in it. Since it is a high compression motor (12.0:1 compression ratio) it can take advantage of the increased energy density of high octane fuel and will produce more torque. If this were five years ago and the engine were fuel injected, it would require premium fuel to run properly. The advantage of direct injection, and more advanced control systems and sensors, is that you can run lower octane fuels without issue if you want to save some money.

I have noticed that i get a bit more low to mid-range grunt when driving on a tank of premium. This helps me get slightly better fuel economy around town, but when i'm doing days of highway driving, the octane rating seems to have less of an effect on fuel economy.

Be careful with randomly filling up any old car with premium, however. With some cars it will do more harm than good, or it will just do nothing. The focus has a pretty snazzy engine, however, which is why you're seeing the improvements.
Originally Posted by cbdallas View Post
"my friend said it can't hurt the car and its "good to clean out the car" with high octane - once a month he said".

This is the point where you stop believing everything you're told. This is also the school of thought that has been making fuel companies rich for decades.

Octane has no cleansing properties, and 93 has no more detergents in it than 87. Different brands of gas differ in their use of detergents, which is why you'll want to stick with top-tier fuel suppliers if cleanliness is a concern.

octane is a pre-ignition eliminator, and that's all it does. It's good to use in higher-compression engines and turbo applications where pre-ignition can occur during high load situations. Pre-ignition manifests itself as spark knock and is akin to striking the tops of the pistons with a hammer.....something you'll want to prevent by using the fuel that's required in your owner's manual.

The 2.0 is engineered to run fine on 87. If you use 89 - 93 octane, you might experience a slight spark timing bump if this engine is set up to detect octane, like the nissan vq and many other engines are. This may yield you a couple of hp, and it may not. There may be a time during a hot summer day, with the a/c on and a car load of people where you accelerate and hear a slight 'ping', and bumping up a grade can eliminate that. But the spark knock detector on your engine is also there to back off the timing a degree or two to put a stop to it, so either way, your engine's best interests are being looked after. If you have excessive spark knock that won't go away, it's time to head to the dealership.

The 2.0t will give you spark advance with higher octane levels, and it's the only way to truly achieve 252 hp with that engine. With the use of 87, i believe it detunes itself to 244. But don't believe what you hear about 'cleaning your engine with octane'. It's simply not true.
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