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So I filled up my car with premium and some injector cleaner. I got less mpg than I get with regular. I would think I'd get more mpg with premium.
Any thoughts?
 

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I wouldn't think it would make any noticeable difference. Unless you have a controlled test using differennt octanes several times to get repeatable results, the difference you experienced could be due to whether or not the tank was filled to the same level in each case.
And maybe the fuel cleaner somehow affected the mileage?
Terry
 

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the 'Duracell Project'
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premium gas has more anti knock stuff in it so you can run higher compression engines with more timing
your best fuel will be the lowest grade you can run
 

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premium gas has more anti knock stuff in it so you can run higher compression engines with more timing
your best fuel will be the lowest grade you can run
Ayuh,.... Exactly,....

Premium is a Waste of money, unless yer motor Needs the less volatile fuel...
 

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Brian Martin,Freelance adviser
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Here is the answer on a thread at ecomodder.com Regular vs. Premium - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

As mentioned here, there is going to be no better without a change in timing, and at that marginal.

Check out that forum guys if you want to help your fuel costs. I was blown away at what I learned. Those guys are as good at fuel milage Hotrodders.com is at making hot rods. Believe it, they know MUCH more about that stuff than you can ever imagine!

Brian
 

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or Jeff, or Doc, or...
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High octane burns colder and needs more compression or timing to fully burn. You'll see higher emissions with that combo too.
Timing is a crutch in this situation. If your cylinder head/piston combo require 36* for regular unleaded to get a clean burn, adding 2 degrees for Premium wont yield ANY additional hp. Match, at best. You didnt change any cylinder pressures with the different fuel. You just lowered combustion temperature.
 
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