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This is a discussion on 91 octane ? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; OK, OK, sorry to cause such a fuss, but I found what I'm looking for. What I was asking is ...

  1. #16
    sss
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    91 octane

    OK, OK, sorry to cause such a fuss, but I found what I'm looking for. What I was asking is what particular mechanical damage does the knocking and detonation incur to the engine?

    Like this kind of stuff:

    from http://www.germanmotorcars.com/Detonation.htm


    Detonation causes three types of failure:

    1. Mechanical damage (broken ring lands, rod bearing failure)

    2. Abrasion (pitting of the piston crown)

    3. Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)


    but they also said

    One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. It's not an optimum situation but it is not a guaranteed instant failure.

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  3. #17
    UnBanned Sinister's Avatar
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    Quote Originally Posted by D0WNxSH1FT View Post
    /banstick
    Very well said turning it around to work for a turbo engine.
    Grassy-ass

    (spanish for thank you, I think)
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  4. #18
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    Quote Originally Posted by sss View Post
    OK, OK, sorry to cause such a fuss, but I found what I'm looking for. What I was asking is what particular mechanical damage does the knocking and detonation incur to the engine?

    Like this kind of stuff:

    from http://www.germanmotorcars.com/Detonation.htm


    Detonation causes three types of failure:

    1. Mechanical damage (broken ring lands, rod bearing failure)

    2. Abrasion (pitting of the piston crown)

    3. Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)


    but they also said

    One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. It's not an optimum situation but it is not a guaranteed instant failure.
    True on older cars, but on a high pressure, high heat, high revving engine such as ours, the chance of mechanical damage increases. We have a very technical engine (I know there's a or 2 out there) We really do. And therefore we don't have as much leeway as, lets say, a 1971 Mustang Mach1. Back then, tuning was a much more general thing, but now we have sensors, and so we push our engines closer to the limit. So you need to be a lot more careful with our 2.0's and 2.5's than you used to with the small black 350's, etc.
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  5. #19
    sss
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    91 octane

    So you're saying that the damage described there is the type of damage you would have with detonation, but detonation is more likely to be destructive with our cars than the ones of the past?

  6. #20
    Registered User D0WNxSH1FT's Avatar
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    Quote Originally Posted by sss View Post
    So you're saying that the damage described there is the type of damage you would have with detonation, but detonation is more likely to be destructive with our cars than the ones of the past?
    Yes especially since our cars are turbocharged.
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  7. #21
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    I would say that if you're not careful that it's easier to get detonation on newer cars if you don't tune them correctly and take care of them properly (91 oct for high perf), and the higher performance the engine is, then the easier it is for the detonation to turn into a larger problem. That's why a lot of todays engines have knock sensors to retard timing if you have detonation problems.
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  8. #22
    UnBanned Sinister's Avatar
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    Also EFI engines are more likely to have problems since they are not mechanically controlled, and the ECU cannot properly manage a runaway engine - one that is knocking/detonating.

    (knocking is when you get pre-detonation.. or when the fuel ignites w/o a spark)
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  9. #23
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    Quote Originally Posted by sss View Post
    Of course, I've been told the 91 octane I get is too cheap and causing a little problem I have, so wtf do I know?
    91 oct is too cheap?? Then go to Cheveron!
    What kind of problems are you having?


    Wow. Are you too cheap to used 91 oct or what?

    Is saving $0.08 a gallon really worth risking the life of your engine?

    If the people who built your car say to use 91 oct. you should probaly use 91 oct. I think they know a little more about your car then you do
    Last edited by Josh04WRX; 07-10-2007 at 11:30 PM.

  10. #24
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    Quote Originally Posted by Josh04WRX View Post
    Wow. Are you too cheap to used 91 oct or what?

    Is saving $0.08 a gallon really worth risking the life of your engine?

    If the people who built your car say to use 91 oct. you should probaly use 91 oct. I think they know a little more about your car then you do
    That wasn't necessary.. he was asking about it. Just learning.. look back. He never said anything about him using anything but 91
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  11. #25
    sss
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    91 octane

    uh, yeah, i'm using 91, it's a hypo!

    Sinister, you said, "That's why a lot of todays engines have knock sensors to retard timing if you have detonation problems.", then wouldn't the knock sensors retard the timing to prevent them?

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    Quote Originally Posted by sss View Post
    uh, yeah, i'm using 91, it's a hypo!

    Sinister, you said, "That's why a lot of todays engines have knock sensors to retard timing if you have detonation problems.", then wouldn't the knock sensors retard the timing to prevent them?
    Correct... But you lose a lot of power, and can still suffer possible detonation. It's basically so that you can get to the next station and fix your mistake.
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  13. #27
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    Quote Originally Posted by Sinister View Post
    That wasn't necessary.. he was asking about it. Just learning.. look back. He never said anything about him using anything but 91
    What are you talking about??? Why dont You Look Back...
    I re-posted his quote for you:


    Quote Originally Posted by zillig04 View Post
    I have used 87 octane in my 04 rex since purchasing it about 5 months ago. I was wondering if anyone had done the same and then reset the ECU to accomodate for changing to 91 or higher octane?

  14. #28
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    Quote Originally Posted by Josh04WRX View Post
    What are you talking about??? Why dont You Look Back...
    I re-posted his quote for you:
    That was in 2004 bro. Look at the dates!
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  15. #29
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    Quote Originally Posted by Sinister View Post
    That was in 2004 bro. Look at the dates!
    Good Job you can Read!

    What the **** is you point?? I made my comment to the OP and you comment me back

  16. #30
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    Quote Originally Posted by Josh04WRX View Post
    Good Job you can Read!

    What the **** is you point?? I made my comment to the OP and you comment me back
    I'm glad you hooked up the OP...

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    Looks like he hasn't been online in a while, so I hope he gets back here just because you hooked him up with your educated comment!
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