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      10-11-2012, 06:19 PM   #14
Stohlen
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Drives: AW 135i
Join Date: Aug 2012
Location: Waterford, Mi

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2008 BMW 135i  [2.83]
Quote:
Originally Posted by Bmwbreed View Post
Well I'll be the first to admit when I'm wrong so if I am forgive me. But I thought when the timing was slowed so was the rate at which fuel was burned. To put it simply a more powerful engine needs more fuel and if you aren't operating at 100% power capacity then it may burn a bit longer. Not necessarily more efficent because its not creating as much power as it could. But I've been wrong before so if I am my apologies. It always felt like tho the few times I had no choice but to use crappy gas in my a4 (premium is limited n north dakota this why we mixed e85 at times) it lasted forever. IDK.
Timing isnt slowed, its retarded, which just means the spark happens earlier. The earlier the spark, the further the piston is from top dead center when combustion starts. Which means more pressure builds that the piston must fight as it rises to top dead center, and thus less horsepower per power stroke.

For example: if an engine run with 87 octane makes 100 hp at 50% throttle, firing 10 degrees before top dead center. And that same engine run on 93 octane makes 105 horsepower at 50% throttle, firing 5 degrees before top dead center. Then you could reduce the throttle of the engine when run on 93 octane to 45% and make 100 horsepower and save some gas, while getting the same amount of power as the 87 octane.
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