89 Octane gasoline

[CJ]

I have used mid grade before many times, anyone who runs more octane then they need is a fool. If you don't have to pull timing on 89, run it.

Interestingly the only place I've ever seen 93 octane is in the DFW metroplex, you never see that high of an octane out of state.

[Ratt]

Premium fuel is bullshit anyways.

Unless you have a tune or FORCED INDUCTION, there is no reason to spend the extra $$$.

I did find out crapstang told my mom to put 87 in her mini cooper sport...(supercharged!!!!) DOH! His excuse was "well it didn't say premium fuel requiered"...............

FTFY. Also, my wife drives a mini cooper non-s model, and it requires 89 or above, so to save a few bucks she uses 89.

there are a few 7-11s with pumps like that in plano

Frisco 7/11s and Quiktrips are like that.

I have used mid grade before many times, anyone who runs more octane then they need is a fool. If you don't have to pull timing on 89, run it.

Interestingly the only place I've ever seen 93 octane is in the DFW metroplex, you never see that high of an octane out of state.

I've never seen 93 anywhere but in the DFW metroplex either.

[Strychnine]

Dude, I've researched it enough. I've heard that California does 91 because of emissions even though I heard the hotter fuel burns, the less emissions

Hotter combustion temps create more NOx emissions. This is why cars have EGR now. Introducing inert gas into the cylinder helps lower the flame temp and keep the combustion below the 1540*F threshold for NOx prodcution.

and the higher the octane, the higher temperature it burns at, creating a more powerful ignition hence the potential power increase.

Octane rating does not affect combustion temperatues, flame speed, energy content, etc.



Background:

** Octane is a number that reprsesents the fuel's resistance to detonation. Nothing more.

** Chemicals, like gasoline and other carbon chain molecules, decompose when heated. Decomposition forms other chemicals which have their own auto-ignition temperature.

** Auto-ignition temperature is the temp at which something will burn without any spark or flame (ex. paper ~ 451*F... hence the title of Bradbury's Farenheit 451, which was about burning books)




There are three things happening when combustion takes place. 1) The flame front moves across the cylinder burning the fuel, 2) the air in the cylinder is heated, and 3) the pressure in the cylinder increases following the Combined Gas Law (p1V1/T1 = p2V2/T2)

It doesn't burn hotter... The flame front moves slower, and is less resistant to going supersonic and forming a shockwave, which causes a ping.

Not quite.

By definition detonation is a "supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it" but in this case it has nothing to do with flamefront speeds and increasing or decreasing that with octane changes (because we know that octane ratings have no effect on flame speed)


Detonation (knock / ping) happens after the fuel has been ignited. The flame front is burning the fuel and propogating outward but the heating of the air is breaking down the carbon chains in the fuel over on the other side of the cylinder before the flame gets there.

As the molecules being heated are broken down they create new compounds and some of these can have auto-ignition temperatures in that range of temps that the cylinder is being heated to via the approaching, but not yet arrived, flamefront.

If that other side lights off then you have an uncontrolled combustion event that will create a its own pressure wave. Now you have two opposing waves, one from each ignition source, that meet in the middle. When they crash they will bounce around off of themselves and the cylinder walls. Combine that with the quicker burning, uncontrolled secondary explosion and you get the "ping" sound. It also creates big spikes in the cylinder pressure which is hard as shit on parts... it's like smashing the piston crown with a hammer instead of giving it a good shove.

So think of octane as the fuel's ability control the burning.


Here's a visual of that push vs the hammer blow

Premium fuel is bullshit anyways.

Unless you have a tune or a s/c, there is no reason to spend the extra $$$.

It's only bullshit if you don't need it. There are naturally aspirated engines that need premium grade just as much as forced induction engines.
Example: My wife's Lexus... 12:1 compression, N/A

[majorownage]

^

What he said.

Supersonic flame front = what ping is.


The coyote motor is 12:1 and can run on 87...but I guess a blanket statement saying all n/a engines can run a piss water is probably going a bit far.

[91CoupeMike]

^

What he said.

Supersonic flame front = what ping is.


The coyote motor is 12:1 and can run on 87...but I guess a blanket statement saying all n/a engines can run a piss water is probably going a bit far.

11:1 sir.

The new mazda 3 is 14:1 lol direct injected though.

[dee]

My 97 Cobra said premium fuel only and with 89 it caused slight pre-detonation.

[A_A_G]

My 97 Cobra said premium fuel only and with 89 it caused slight pre-detonation.

Why be a cheapass and potentially cause damage to save $5 a tank?

[bcar]

I run the cheapest fuel I can find in the vette.



















E85

[89stangGT]

Regular is 87. 91 is considered premium in California. 89 octane gas is the most useless shit ever.

they have 90 octane as premium in west Texas, and all the way from west TX to Cali premium is no better than 91.

[89stangGT]

Need more variety? I took this pic last night in Stillwater OK

I saw that kind of variety at the Walmart in Tyler, TX.

[89stangGT]

my car manual says you can use 89, but only if you have no other choice. Recommends nothing less than 91. Turbo motor. I only run Shell 93.

I put QT's 93 octane in once and got a CEL. Filled up next time with Shell and it went away. As a test, used QT the next time and it came back on lol. So, went back to Shell 93 and it went off. The code for the CEL was the o2 sensor. Doesn't help my downpipe has a single, crappy high flow cat.

[dee]

Why be a cheapass and potentially cause damage to save $5 a tank?

I lived out In the middle of nowhere then and that's all the local station had till I got to town, just put enough in to get me there kept it under 3000 and didn't have any ping.

[majorownage]

My 97 Cobra said premium fuel only and with 89 it caused slight pre-detonation.

lulz

Bullshit.

b headed cobras run wot afrs in the 10s and a pathetic amount of spark.

[Dawkins]

I parked my TA after I built the motor to run on 93 and I cannot get anything over 90 here. No e85 either. Gas this far out is shit.

Just another reason I miss Dallas.

[dee]

lulz

Bullshit.

b headed cobras run wot afrs in the 10s and a pathetic amount of spark.

Since you drove the car you must know, right?