Detonation...
#1
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Joined: May 2012
Posts: 43
From: Washington
Car Info: 2005 Subaru WRX STi
Detonation...
I was talking with my mechanic lately about the subject of detonation, but he really wasn't too specific on what it actually was... he just said something about not using 87 oct. gas for my STi, to just use 91 and up... What IS detonation?
#2
detonation happens when the fuel ignites before the piston reaches the top of the cylinder. Its bad because it pushes back at the piston instead of pushing it forward. It shows up as a "knocking" sound which is why cars are equipped with a "knock" sensor which will cause your car to pull timing to avoid further detonation.
Using the correct grade fuel for your car is important but in a pinch lower octane fuel will work but you will have reduced power as a result.
Using the correct grade fuel for your car is important but in a pinch lower octane fuel will work but you will have reduced power as a result.
#3
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From: Cheesesteakville
Car Info: 05 wrx wagon, 90 celica alltrac, 66 mustang
Close Marioshi but it sounds like you are describing pre-ignition.
Engine knocking - Wikipedia, the free encyclopedia
Knock or detonation is when the explosion of air and fuel is irregular yet still initiated by the spark plug.
Engine knocking - Wikipedia, the free encyclopedia
I am no expert though.
Engine knocking - Wikipedia, the free encyclopedia
Knock or detonation is when the explosion of air and fuel is irregular yet still initiated by the spark plug.
Engine knocking - Wikipedia, the free encyclopedia
I am no expert though.
#4
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From: Rohnert park/SSU
Car Info: 2006 SGM wrx wagon
When I had my car tuned in Washington with 92 octane and then moved down here and started using 91 octane I started getting detonation. Basically, I would floor it in 3rd, 4th, or 5th gear and at around 3k rpms when the turbo would spool I would get a kind of crackling sound with a little hesitation and then it would go away. Didn't know what it was until I saw this dyno video DETONATION - YouTube --> that's what detonation sounds like.
#5
Close Marioshi but it sounds like you are describing pre-ignition.
Engine knocking - Wikipedia, the free encyclopedia
Knock or detonation is when the explosion of air and fuel is irregular yet still initiated by the spark plug.
Engine knocking - Wikipedia, the free encyclopedia
I am no expert though.
Engine knocking - Wikipedia, the free encyclopedia
Knock or detonation is when the explosion of air and fuel is irregular yet still initiated by the spark plug.
Engine knocking - Wikipedia, the free encyclopedia
I am no expert though.
Bottom Line: Put the recommended octane in your car to avoid reduced power and/or damage to your engine. your mechanic is correct about this.
You are correct that my limited explanation did seem to describe pre-ignition once I went back and read it
Last edited by Marioshi; 05-10-2012 at 01:26 PM.
#6
91 octane is fine as long as you're not running a tune meant for 93 or higher. You can't run low or midgrade octanes unless you absolutely have to because it's all that's available and you stay out of boost. Your stock ECU will retard timing when it starts detonating as a self-preservation method but will eventually start to advancing it again until you start knocking once more. If you keep using 87 you're gonna constantly run into the retard -> detonation -> retard -> detonation cycle and that can lead to you replacing the motor.
Last edited by Brfatal; 05-10-2012 at 06:30 PM.
#8
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From: Cheesesteakville
Car Info: 05 wrx wagon, 90 celica alltrac, 66 mustang
Down here in California all that is commonly available is 91. I try to only go to 76's that have one nozzle per grade of fuel so I do not get a little 87 with my 91. If I have to take from multi-grade nozzles I stay out of boost until I can top of with a gallon or two of 100. Some people think I am nuts for doing this.
#10
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Joined: May 2012
Posts: 43
From: Washington
Car Info: 2005 Subaru WRX STi
Thanks everyone for your help. I HAVE been running 92 since I got it, and I dont plan to go any lower unless I absolutely need to... I was just curious on what detonation actually meant. I really appreciate you guys answering my question.
#11
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Joined: May 2012
Posts: 43
From: Washington
Car Info: 2005 Subaru WRX STi
I see that detonation is DEFINATELY not good, but I also have heard of people like running higher octane fuels like Citgo 110 leaded fuel... what would something like that do to your motor?
#12
For you running 91, a little bit more power. I've read that our ECUs might advance enough for anything up to 95 octane to be beneficial. Anything after that will require tuning to take advantage of.
Last edited by Brfatal; 05-11-2012 at 04:47 PM. Reason: spelling
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