Armando Kulas

What Octane Rating of fuel should I use?

43 posts in this topic

i use 91.. i guess youre not in the us getting 93 or 95 .. not california anyway.. theres a noticeable difference to me in performance versus 87.. both will work fine.. the higher octane is peppier..

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I would love a believer of the premium gas myth to provide some sort of emissions or dyno graph to prove you get more power and economy from 93 vs 87. Also a procedure in how they did the testing. I work in a vehicle lab where we test these kind of things.

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87 octane has quicker combustion at lower temp and the higher octanes combust at a higher temp and burn more slowly to prevent 'pre-combustion' resulting in engine knock. Higher octane does not in any way give better performance in cars that can run the regular octane...that is a long standing myth ie: higher number + higher price = better performance quality etc.

Bottom line: low octane burns fast and ignites at a lower temp, high octane burns slow and ignites at a higher temp. simply designed for high compression engines such as found in some performance domestic cars with high compression ratios such as 12/1 etc.

1LoudLS likes this

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I have a 2015 Chevy spark 5spd. I get an average of 35mpg. The best I've ever got was 56mpg. I was cruising at 45mph-70mph through a mountain pass where I live around. I found out that if I fill up with 92 octane rather than 87 I don't have to shift from 5th to 4th as much as I would if I filled up with 87. Also I get about an average of 8 more mile a gallon if I use 92 than 87. Top tier gas is better mpg as well. I prefer chevron or Texaco. They are expensive but I have done a lot of driving around I found out which one gives me the best. Also I can get like 70 mpg if I fill up on 92 octane non ethanol gas. Not sure how that plays out but I love it. But I don't like pay $4 per gallon when gas is $3. But I've done lots of driving. I drove both auto and manual sparks and the manuals have way more get up and go then the automatics. 

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On 9/27/2016 at 4:34 AM, YeeYee! said:

I have a 2015 Chevy spark 5spd. I get an average of 35mpg. The best I've ever got was 56mpg. I was cruising at 45mph-70mph through a mountain pass where I live around. I found out that if I fill up with 92 octane rather than 87 I don't have to shift from 5th to 4th as much as I would if I filled up with 87. Also I get about an average of 8 more mile a gallon if I use 92 than 87. Top tier gas is better mpg as well. I prefer chevron or Texaco. They are expensive but I have done a lot of driving around I found out which one gives me the best. Also I can get like 70 mpg if I fill up on 92 octane non ethanol gas. Not sure how that plays out but I love it. But I don't like pay $4 per gallon when gas is $3. But I've done lots of driving. I drove both auto and manual sparks and the manuals have way more get up and go then the automatics. 

 

 

Sorry man, you did math wrong, the DIC on your Spark is reading wrong, or you just want to believe that the money you're spending is accomplishing something.

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On 9/28/2016 at 7:42 AM, SpaceCowboy said:

 

 

Sorry man, you did math wrong, the DIC on your Spark is reading wrong, or you just want to believe that the money you're spending is accomplishing something.

Lower Octane gas combustion is faster and more complete and is what the Spark engine runs best on. I think you have your DIC units set to Canadian or Euro Gallons which are more volume, thus the perception of higher MPG. Check your owners manual on how to set the DIC display for US gallons. There is a widespread misconception that higher Octane equals more potent gas...not true..higher Octane is designed for engines with high compression and no variable timing for a slower combustion to prevent knocking or precombustion..by using higher octane the timing will advance to compensate and can occasionally give some xtra power when the knocking is sensed by the knock sensor..this is hard on the engine in the long run and will give you more carbon build up due to incomplete combustion between timing changes as speed and temp vary. A stock Spark that relies heavily on sensors making everything from ignition to valve timing variable at different conditions. The best running Sparks are ones that use correct octane quality gas, synthetic oil and tires inflated to about 42psi...clean OEM or non-oiled hi-flo filters and a fuel tank that is never driven to almost empty since the fuel pump, submerged in the tank, needs the gas level to be high enough to keep it cool..I have seen our Pizza guy run his '13 auto tranny over 180Kmi..no real issues and still runs like new. Any engine mods will only be negated by the many sensors to compensate for any change.

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On 9/30/2016 at 5:09 AM, Retired old Gearhead said:

Lower Octane gas combustion is faster and more complete and is what the Spark engine runs best on. I think you have your DIC units set to Canadian or Euro Gallons which are more volume, thus the perception of higher MPG. Check your owners manual on how to set the DIC display for US gallons. There is a widespread misconception that higher Octane equals more potent gas...not true..higher Octane is designed for engines with high compression and no variable timing for a slower combustion to prevent knocking or precombustion..by using higher octane the timing will advance to compensate and can occasionally give some xtra power when the knocking is sensed by the knock sensor..this is hard on the engine in the long run and will give you more carbon build up due to incomplete combustion between timing changes as speed and temp vary. A stock Spark that relies heavily on sensors making everything from ignition to valve timing variable at different conditions. The best running Sparks are ones that use correct octane quality gas, synthetic oil and tires inflated to about 42psi...clean OEM or non-oiled hi-flo filters and a fuel tank that is never driven to almost empty since the fuel pump, submerged in the tank, needs the gas level to be high enough to keep it cool..I have seen our Pizza guy run his '13 auto tranny over 180Kmi..no real issues and still runs like new. Any engine mods will only be negated by the many sensors to compensate for any change.

 

not telling me anything i don't know.

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"not telling me anything i don't know."

I realize that working in a vehicle lab that you would know the facts on this..but my post was meant to enlighten the "Yee-Yee" poster who seemed not to have any concept of how Octane works, with a few other items thrown in to help him understand this widely misunderstood concept that higher Octane equals better performance. Now that I have your attention, working in a lab that tests this kinda stuff, do you have any facts or opinion on the addition of 10% ethanol? OH..while I'm here..not sure if you work with brake fluids, but what is the reason brake fluid is recommended to be changed every 40-50Kmi or so. That is something I would really like to know as in previous vehicles I have never changed it.

Edited by Retired old Gearhead

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4 hours ago, Retired old Gearhead said:

"not telling me anything i don't know."

I realize that working in a vehicle lab that you would know the facts on this..but my post was meant to enlighten the "Yee-Yee" poster who seemed not to have any concept of how Octane works, with a few other items thrown in to help him understand this widely misunderstood concept that higher Octane equals better performance. Now that I have your attention, working in a lab that tests this kinda stuff, do you have any facts or opinion on the addition of 10% ethanol? OH..while I'm here..not sure if you work with brake fluids, but what is the reason brake fluid is recommended to be changed every 40-50Kmi or so. That is something I would really like to know as in previous vehicles I have never changed it.

 

I work for the EPA testing vehicles for emissions and fuel economy.  10% ethanol is going to lower mileage very slightly because it has less BTU's than equivalent gasoline.  Hence why when you have a vehicle that will run on e85 it will roughly get 33% less mpg.

 

As far as brake fluid I am far from an expert but, brake fluid absorbs moisture.  When this happens it lowers the boiling point which in time can cause a spongy pedal. Also when brake fluid gets dark it has been contaminated.  

 

That's my 2 cents

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Thanx SpaceCowboy!...I forgot about the brake fluid absorption. Both the Spark and my Range rover '15 (V8-540HP) have absolutely no odor at exhaust once engine is up to temp. I know today's cars are cleaner..which unit of the ones you have tested is the cleanest?

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On 10/6/2016 at 5:48 AM, Retired old Gearhead said:

Thanx SpaceCowboy!...I forgot about the brake fluid absorption. Both the Spark and my Range rover '15 (V8-540HP) have absolutely no odor at exhaust once engine is up to temp. I know today's cars are cleaner..which unit of the ones you have tested is the cleanest?

 

Electric cars seem to be the cleanest on emissions testing ;).  In my 9 years I've tested hundreds of vehicles.  The small displacement hybrids are probably the second cleanest to electric cars.

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I'm sorry, but anybody that thinks they are getting any better performance from higher octane fuel is just arguing against science. you are no different than people that still think the earth is flat or that we haven't been to space. they oblivious work in a profession that is far different from that of engineers that design engines, engineers that test those engines, technitions that built or work with high performance engine building or that work in engine tuning.  those people actually work in science, they are actually doing the math and need to know what the difference in octane actually is and what it means during the combustion cycle.   

 

in a modern fuel injected automobile, for the most part, the compression ratio, air temps, and how aggressive the engines calibration or "tune" is, are what dictate what octane fuel the car needs to be fed. none of that is really that high in the case of the spark, if the compression ratio was high enough, fuel with lesser octane would ignite too early causing pre detonation which will eventually(or very quickly depending on the severity) destroy your motor probably by throwing a rod right through the block.

 

if the air intake tempature was hot enough like it was being compressed by a turbo, that added with too much compression would cause the air/fuel to ignite to early causing............  

but with ambient air not being compressed before being fed to the engine means that wont be a problem causing you to need a high octane fuel.

 

in regards to engine tuning, if it was aggressive enough be having a lot of spark advance, then you would need a high octane to keep the air/fuel mix from igniting too early causing............  

but luckily the GM engineers though of that and when the knock sensor starts to detect pre detonation, it retards the timing enough to keep that from happening and preventing the motor from blowing itself apart. they also know that the spark is not a Z06 and build the engine for efficiently not full on performance and therefor tune it to walk a balance of longevity and efficiency. the stock tune is very mild and as long as your your meeting the minimum requirements, the PCM wont need to pull any timing to keep it safe, but it also is not pushing the edge and after the minimum is met, it wont push harder than its programmed to do. now if the spark had an aftermarket tune, then the tuner would likely push the timing up a few degrees making use (and requiring) higher octane. but without that, there is truly no benefit to a high octane fuel, doesn't matter if its 91, 92, Corn E85(which is really equivalent to over 100) or VP racing 114, all that extra octane is not making your bang any more powerful in your low compression engines.

 

long story short, you want the precisely controlled spark from the spark plug, not the inconsistent heat from the compression cycle to ignite the air/fuel mix. and if that precisely controlled spark is not programmed to take advantage of the benefit of higher octane fuel, then there is no more power to be made, their is no more mileage to be made, there is no measurable difference to be found.  your engine will only suck so much air in on its own, that air will only have so much oxygen contained in it, that oxygen can only allow a very specific amount of fuel to be burned with it. octane changes none of that

 

#SuckSqueezeBangBlow

#MathAlwaysWins

#BecauseRaceCar

 

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On 10/6/2016 at 5:48 AM, Retired old Gearhead said:

which unit of the ones you have tested is the cleanest?

 

my money is on it not being Voltswagon/Audi... :lol:

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From my experience, 87 is fine at 100 degrees and below. Mid-range  for 101-115 stops it from trying to stall out. Highest octane  gives it random bursts of acceleration.

(Of course, all deemed normal by the dealership)

Edited by VegasSpark

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if higher octane was truly responsible for burst of acceleration, why would they be random? it either does or it doesn't.

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16 hours ago, 1LoudLS said:

if higher octane was truly responsible for burst of acceleration, why would they be random? it either does or it doesn't.

Ive only seen the burst of acceration while using the highest octane. And since that was the only change at that point, and didnt happen after i switched back, i was under thr assumption that it had something to do with the octane.

 

Or my car is possesed. ;)

Edited by VegasSpark

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On 11/5/2016 at 6:26 PM, VegasSpark said:

Ive only seen the burst of acceration while using the highest octane. And since that was the only change at that point, and didnt happen after i switched back, i was under thr assumption that it had something to do with the octane.

 

Or my car is possesed. ;)

 

Do you have a calibrated butt that can feel the difference between 13.9 seconds 0-60 compared to 14.0?  Placebo effect of putting money in the gas tank.

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On Monday, November 07, 2016 at 9:23 AM, SpaceCowboy said:

 

Do you have a calibrated butt that can feel the difference between 13.9 second 0-60 compared to 14.0?  Placebo effect of putting money in the gas tank.

No... more so like steady pressure on the pedal, and it shoots forward for half a second or so like i slammed on the gas, then dropping back down to normal.

Though it just had its brain replaced and hasnt actes up since, so that might have been the root cause of it all.

Though the dealer did think it was vapor locking during the summer...

Edited by VegasSpark

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