Ask the Mechanic

Running on Octane

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READER: With the current price of gas per gallon skyrocketing, I have thought about running lower-octane-rated gas in my trucks. The 5.7 Hemi that I have in one truck does not call for high-octane gasoline, but I have been running the high-octane-rated gas in it. The other truck is a Chevy with a 6.2 engine, and high-octane fuel is suggested for that engine. What are your thoughts on the use of these two fuels in these engines?

STEVE: If the engine manufacturer recommends lower fuel octane rating for the Ram 5.7 engine, then that is what I recommend. Save yourself some money. You will probably not notice any change in performance since your engine is tuned for that fuel. The Chevy 6.2 engine calls for higher-octane fuel, which is usually required in engines with higher compression ratios. The Chevy with a 6.2 is a fast truck, and the engine is built differently than its older brother, the 6.0. The 6.2 likes the slower burn of the higher-octane fuel as it pushes the piston down longer on the power stroke than the lower-octane fuels. The higher the octane, the slower the burn.

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-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email mechanic@progressivefarmer.com, and be sure to include your phone number.

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