I need a simple,easy to understand explanation please. I drive an 05 GT. She gets 87 octane at every fill up. No engine mods. She drives fine, no engine problems. From day one, my B-I-L has wanted to put racing fuel in her. I say "no" she runs fine. He says she needs a higher octane from time to time to clean her out. Again, I say "no". I'm about to take a 7-800 mile round trip. He says higher octane fuel with an octane boost additive is a must-make the motor purr like a kitten. What's the deal? She runs fine and gets great MPG. (27 hwy) He runs higher octane in all of his motors and adds octane boost and sometimes runs racing fuel. Will it hurt my GT? Would it just be a waste of $? Will it increase performance, MPG? Will it spoil her to the point of always needing the "good stuff"? BTW, I use Texaco fuel around home, Shell or Chevron when Texaco is not an option. Never use no name brand or Citgo.
I am sure others will chime in, but an engine is "tuned" to a particular octane, ie, timing issues. Putting in a higher octane gas will do nothing for performance or the engine.
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Gas is 2 molecules, Heptane and Octane. Heptane ignites super easily under pressure, and octane does not. Therefore, the higher concentration octane you have, the higher compression you can run in your motor without the fuel igniting prematurely. But, if your car is not tuned for the higher octane, you will see no advantage from it, in fact it might hurt the motor because it wont run right. Higher octane is better than lower if you cant get 87, but racing fuel is a horrible Idea.
Octane rating simply put is a number that reflects the fuel's ability to suppress detonation. Another factor is burn rate. The higher the number, the slower the burn rate. You should run the fuel that is required for the tune present in the car's pcm. You will probably decrease your mileage with a higher octane fuel because of the slower burn rate. Your BIL is all wet.
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Not to mention that racing fuel is leaded and will damage the catalytic converters. If you do not have higher compression, nitrous, a blower, and some actual reason to go with higher octane, then you will not see any benefit of it other than a lighter wallet. The higher octane fuel burns slower and is how it fights off detonation as jgard said.
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He says higher octane fuel with an octane boost additive is a must-make the motor purr like a kitten.
"Octane boost additive" will gum up your engine. There have been several threads on AFM to that effect. To review:
1. Adds nothing.
2. BAD for the 3-valve engine.
Quote:
Originally Posted by 65205
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I use Texaco fuel around home, Shell or Chevron when Texaco is not an option. Never use no name brand or Citgo.
Texaco and Shell merged a couple years ago. It's now "Texaco/Shell." Same source. All of the Texaco signs around where I live have been converted to Shell. In some areas, its one or the other, but that is just a marketing program. Ya' picks one, ya' pays yer nickels. Same deal.
Oh, and while Citgo is a brand name, big ups to you for letting Hugo suck dry pumps. Scroom.<== Say it fast three times.
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I need a simple,easy to understand explanation please. I drive an 05 GT. She gets 87 octane at every fill up. No engine mods. She drives fine, no engine problems. From day one, my B-I-L has wanted to put racing fuel in her. I say "no" she runs fine. He says she needs a higher octane from time to time to clean her out. Again, I say "no". I'm about to take a 7-800 mile round trip. He says higher octane fuel with an octane boost additive is a must-make the motor purr like a kitten. What's the deal? She runs fine and gets great MPG. (27 hwy) He runs higher octane in all of his motors and adds octane boost and sometimes runs racing fuel. Will it hurt my GT? Would it just be a waste of $? Will it increase performance, MPG? Will it spoil her to the point of always needing the "good stuff"? BTW, I use Texaco fuel around home, Shell or Chevron when Texaco is not an option. Never use no name brand or Citgo.
As many have already stated, you are doing the correct thing is using the 87 oct. as you state the car is running fine, why mess with it. Keep doing the 87 oct as it was intended for, and in addition you are getting 27mpg highway, that is fantastic. Tell B-I-L to leave your car alone.
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Thanks for all of the replies! I've taken notes...can't wait for our next talk! He's a great guy and has always been helpful. He freely admits that he is old school and the computers running today's cars are a bit of a mystery. I know I'll never change his mind, but I feel better now about sticking with the 87. Silly, I know.
Gotta love brother in laws....there's no benefit in running higher octane if your cars tuned for 87.....well there is one, but it goes to the oil company.
I found that my engine would always "knock" when accelerating using Shell/BP 87 octane (with 10% ethanol)...so I switched to 89 (mid-grade) octane and the knock is gone...haven't heard it since...
Can someone explain octane? 
for letting Hugo suck dry pumps. Scroom.<== Say it fast three times.
Tell B-I-L to leave your car alone.
- Her Toy. 
