Why does 2 Octane make such a difference?

[Gand1]

Small story....

I drive a 95 Mazda Protege, not the baddest performance car out there (I always say it's not what you drive but how you drive it anyway). Anyhow, since gas has been a bit more expensive lately, I have been putting the regualr stuff in. With that the car pings and knocks like there is no tomorrow! I normally buy my gas from Mobile/Exxon due to the fact it is the most convienient for me. Yeah, yeah, big bad oil companies, whatever... So the other day I decided to stop at my brand spankin new Wawa and fill up with the better grade stuff. 89 octane instead of 87. The pings and knocks stopped almost instantly! Whoah! So can someone explain how only 2 octane made that much of a difference and is Wawa gas actually better than Mobile/Exxon? I always assumed Mobile/Exxon was a bit more expensive due to, well yeah the big oil thing and the more consistant level of detergents and addatives (makes car run better?).

Wha happen?

 

[DivideBYZero]

Flame front is slower. Prevents Detonation (pinging).

/Thread.

 

[iamwiz82]

Perhaps you should be looking into why your 95 Protege is pinging rather than hiding the problem.

 

[jamesbond007]

Where I work, we dropped Mobile gas because of the cost...we bring ing our own branded gas to control our cost and pricing better. My manager said that Mobile adds a solution to their stuff to brand it and to do some other stuff...maybe it really is worth the premium? Perhaps you are mixing a bit too much ethanol with the new stuff? I know some cars can't take it because of the higher temps ethanol puts on car parts.

Originally posted by: DivideBYZero
Flame front is slower. Prevents Detonation (pinging).

/Thread.

Can you explain this?

 

[Siddhartha]

Originally posted by: iamwiz82
Perhaps you should be looking into why your 95 Protege is pinging rather than hiding the problem.

As cars age they develop cylinder carbon build up. This causes an effective rise of the engines compression ratio. As an engine compression ratio goes up it requires the use of fuel with higher octane ratiings to prevent pinging or preignition detonation.

An engine rebuild will fix this.

 

[DivideBYZero]

Most engines built in the last 5 years should have a 'knock' (this is Pinging, knocking, pinking whatever you want to call it) sensor and adjust the timing to compensate for low octane fuel.

If you just put some in maybe it's taking a couple of miles to adjust, or the sensor is buggered, or I'm completely on the wrong track and like Sid says there is another reason.

Good luck.

 

[Howard]

Originally posted by: Siddhartha

Originally posted by: iamwiz82
Perhaps you should be looking into why your 95 Protege is pinging rather than hiding the problem.

As cars age they develop cylinder carbon build up. This causes an effective rise of the engines compression ratio. As an engine compression ratio goes up it requires the use of fuel with higher octane ratiings to prevent pinging or preignition detonation.

An engine rebuild will fix this.

That'd be a hell of a lot of carbon to make a difference.

 

[DivideBYZero]

Originally posted by: jamesbond007
Where I work, we dropped Mobile gas because of the cost...we bring ing our own branded gas to control our cost and pricing better. My manager said that Mobile adds a solution to their stuff to brand it and to do some other stuff...maybe it really is worth the premium? Perhaps you are mixing a bit too much ethanol with the new stuff? I know some cars can't take it because of the higher temps ethanol puts on car parts.

Originally posted by: DivideBYZero
Flame front is slower. Prevents Detonation (pinging).

/Thread.

Can you explain this?

Dug this up for ya:

Higher-octane fuel isn't harder to ignite in the usual way (that is, with a spark); the octane rating just indicates how easily the fuel can SPONTANEOUSLY ignite before the flame-front reaches it. "Spontaneous pre-ignition" is just another phrase for "detonation" or "knock"; higher-octane fuels resist knocking better than low-octane fuels.

Diesel engines rely on Sponatneos ignition under compression and heat, but this is bad in Petrol engines as they rely on the computer to time the spark.

 

[Gand1]

Guys thanks for the answers!!

Engine rebuild... ha! Oh yeah, I did leave out the fact the car/engine has 250,000 miles on it!

Can I get a badge from Mazda for that!

 

[Siddhartha]

Originally posted by: Gand1
Guys thanks for the answers!!

Engine rebuild... ha! Oh yeah, I did leave out the fact the car/engine has 250,000 miles on it!

Can I get a badge from Mazda for that!

I put that in response to the "find out whats wrong instead of hiding it comment"...

 

[Minjin]

Originally posted by: Howard

Originally posted by: Siddhartha

Originally posted by: iamwiz82
Perhaps you should be looking into why your 95 Protege is pinging rather than hiding the problem.

As cars age they develop cylinder carbon build up. This causes an effective rise of the engines compression ratio. As an engine compression ratio goes up it requires the use of fuel with higher octane ratiings to prevent pinging or preignition detonation.

An engine rebuild will fix this.

That'd be a hell of a lot of carbon to make a difference.

At 250k? Very possible. Turbo cars are especially known for doing this because they often run very rich from the factory. His Protege may have been run with a bad o2 sensor for some time, causing it to run very rich.

OP, do a search on Mopar Combustion Chamber Cleaner and follow one of the many instruction pages. I believe some people use a product known as Seafoam as well.

Mark

 

[jamesbond007]

Originally posted by: DivideBYZero

Originally posted by: jamesbond007
Where I work, we dropped Mobile gas because of the cost...we bring ing our own branded gas to control our cost and pricing better. My manager said that Mobile adds a solution to their stuff to brand it and to do some other stuff...maybe it really is worth the premium? Perhaps you are mixing a bit too much ethanol with the new stuff? I know some cars can't take it because of the higher temps ethanol puts on car parts.

Originally posted by: DivideBYZero
Flame front is slower. Prevents Detonation (pinging).

/Thread.

Can you explain this?

Dug this up for ya:

Higher-octane fuel isn't harder to ignite in the usual way (that is, with a spark); the octane rating just indicates how easily the fuel can SPONTANEOUSLY ignite before the flame-front reaches it. "Spontaneous pre-ignition" is just another phrase for "detonation" or "knock"; higher-octane fuels resist knocking better than low-octane fuels.

Diesel engines rely on Sponatneos ignition under compression and heat, but this is bad in Petrol engines as they rely on the computer to time the spark.

Wow, thanks for the detailed response!

 

[FrustratedUser]

Originally posted by: Gand1
Small story....

I drive a 95 Mazda Protege, not the baddest performance car out there (I always say it's not what you drive but how you drive it anyway). Anyhow, since gas has been a bit more expensive lately, I have been putting the regualr stuff in. With that the car pings and knocks like there is no tomorrow! I normally buy my gas from Mobile/Exxon due to the fact it is the most convienient for me. Yeah, yeah, big bad oil companies, whatever... So the other day I decided to stop at my brand spankin new Wawa and fill up with the better grade stuff. 89 octane instead of 87. The pings and knocks stopped almost instantly! Whoah! So can someone explain how only 2 octane made that much of a difference and is Wawa gas actually better than Mobile/Exxon? I always assumed Mobile/Exxon was a bit more expensive due to, well yeah the big oil thing and the more consistant level of detergents and addatives (makes car run better?).

Wha happen?

1. What octane do Mazda recommend?
2. Use that
3. ...
4. Profit.