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Is there a point in "Plus" grade fuel?

Castiel

Castiel

Golden Member
Here in Pennsylvania we have

Regular - 87 Octane
Plus - 89 Octane
Supreme - 93 Octane

Whats the point in even having "Plus" or am i just asking a question that i'll never get an answer for?
 
Well, older cars can sometimes have enough buildup of carbon in the combustion chamber to raise their compression ratio just enough to ping on regular, and moving to a mid-grade gas will stop that pinging.
 
Meghan54 said:
Well, older cars can sometimes have enough buildup of carbon in the combustion chamber to raise their compression ratio just enough to ping on regular, and moving to a mid-grade gas will stop that pinging.
Click to expand...

Or if you're trying to cheap out by putting cheap fuel in your BMW and it pings you can try using the mid grade and hoping that doesn't ping
 
Octane is a combustion inhibitor - fuels with higher octane actually burn more slowly than fuels with lower octane, but contain the same amount of energy.

Higher octane is only needed for high performance engine that would exhibit pre ignition, or knock, with regular fuel. It also depends on the altitude you are at, or more specifically, the air pressure. Lower air pressure means you can get away with lower octane fuel, higher air pressure means you need higher octane fuel to prevent pre ignition.
 
Exactly, higher octane is needed for high performance, high compression motors. Jo Bl0 is his Civic doesn't need it.
 
Ancalagon44 said:
Octane is a combustion inhibitor - fuels with higher octane actually burn more slowly than fuels with lower octane, but contain the same amount of energy.

Higher octane is only needed for high performance engine that would exhibit pre ignition, or knock, with regular fuel. It also depends on the altitude you are at, or more specifically, the air pressure. Lower air pressure means you can get away with lower octane fuel, higher air pressure means you need higher octane fuel to prevent pre ignition.
Click to expand...




What you're describing is detonation, not pre-ignition....but many, many people get the two confused.

Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.

Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion, it is classified as pre-ignition. The two are completely different and abnormal phenomenon.


Using the improper grade of gas and the resultant knocking/pinging heard is detonation. Just an FYI.
 
ShawnD1 said:
Or if you're trying to cheap out by putting cheap fuel in your BMW and it pings you can try using the mid grade and hoping that doesn't ping
Click to expand...

I do this with my MINI. The manual says that I should use 91, but 87 will work with some possible loss of performance.

I found that the car runs lousy on 87, but anything above 89 runs great in it. The engine runs smooth, and I'm averaging 40 MPG.
 
Last edited:
my civic requires 91, and i've been in bumfuck, nowhere, where the 91 pump was broken, so i put in 89 instead of 87. so i guess it did serve me some purpose that day.
 
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