FUEL: Premium versus Regular
Racer
Joined: Jan 2015
Posts: 388
Likes: 6
From: Far West
The higher the altitude the lower the lower the Octane needed.
Octane is the ability of a fuel to resist knock, and high-compression engines tend to knock more. The obverse of that is that lower-compression engines can run on lower-octane gas. Air is thinner the higher above sea level you go. Less air going into the cylinders means less pressure at top dead center when things go bang. It's a lot like lowering the compression ratio in the engine, reducing the need for high octane. Cars will run just fine on lower-octane fuel when they're well above sea level.
For each 1,000 feed one's compression ratio drops approximately 3%. Here in Utah we are at 5,000 ish feet. Thus our compression rations are 85% of what sea level C-7s run.
I've used middle grade gas (87-89 Octane here) on high performance engines at our higher altitudes for decades and NEVER had any problems with knocking or performance.
My $.02
PS: Regular Fuel here is 85 Octane.
Octane is the ability of a fuel to resist knock, and high-compression engines tend to knock more. The obverse of that is that lower-compression engines can run on lower-octane gas. Air is thinner the higher above sea level you go. Less air going into the cylinders means less pressure at top dead center when things go bang. It's a lot like lowering the compression ratio in the engine, reducing the need for high octane. Cars will run just fine on lower-octane fuel when they're well above sea level.
For each 1,000 feed one's compression ratio drops approximately 3%. Here in Utah we are at 5,000 ish feet. Thus our compression rations are 85% of what sea level C-7s run.
I've used middle grade gas (87-89 Octane here) on high performance engines at our higher altitudes for decades and NEVER had any problems with knocking or performance.
My $.02
PS: Regular Fuel here is 85 Octane.
Last edited by ILuvUMan; Feb 11, 2015 at 09:20 AM.
Burning Brakes
Joined: Jan 2001
Posts: 777
Likes: 120
From: CT
This always puzzles me. you drive a 60K+ car. Why in the world would you want to skimp on the gas? as mentioned earlier, you're typically looking at a $2-$3 difference per tank. If you are really hard up for the couple of bucks, you need to re-evaluate your decision to buy an expensive car. If you just don't want to give the car the best fuel you can give it (which is what the mfg recommends anyway) then once again, you need to re-evaluate your decision to buy this car. lol
And I understand the exception for high altitudes...
Drifting
Joined: Sep 2014
Posts: 1,319
Likes: 436
I don't know how much more obvious it can be when it says:
If equipped with the LT1 engine, use
premium unleaded gasoline meeting
ASTM specification D4814 with a
posted octane rating of 91 or higher.
Apparently that's too difficult for people around here to understand...
If equipped with the LT1 engine, use
premium unleaded gasoline meeting
ASTM specification D4814 with a
posted octane rating of 91 or higher.
Apparently that's too difficult for people around here to understand...
And yet you stop reading..... Go a little farther grasshopper..
Thread Starter
Burning Brakes
Joined: Jan 2005
Posts: 796
Likes: 444
From: Miami & Naples, FL
Unmodified C8 of the Year 2021 Finalist
Premium versus regular
It amazes how many people do not answer the question. Some of you are just down right rude! 
My question has NOTHING to do with the cost of the fuel, or my ability to pay for it.
I am asking whether after a year of real world use, has anyone had trouble running regular fuel?
New 2015 on the way, and if I get caught running a tank of regular fuel because my local station runs out - has this caused anyone any trouble?
My question has NOTHING to do with the cost of the fuel, or my ability to pay for it.
I am asking whether after a year of real world use, has anyone had trouble running regular fuel?
New 2015 on the way, and if I get caught running a tank of regular fuel because my local station runs out - has this caused anyone any trouble?
Le Mans Master
Joined: Jun 2014
Posts: 7,474
Likes: 116
From: Over there
It amazes how many people do not answer the question. Some of you are just down right rude!
My question has NOTHING to do with the cost of the fuel, or my ability to pay for it.
I am asking whether after a year of real world use, has anyone had trouble running regular fuel?
New 2015 on the way, and if I get caught running a tank of regular fuel because my local station runs out - has this caused anyone any trouble?
My question has NOTHING to do with the cost of the fuel, or my ability to pay for it.
I am asking whether after a year of real world use, has anyone had trouble running regular fuel?
New 2015 on the way, and if I get caught running a tank of regular fuel because my local station runs out - has this caused anyone any trouble?
I wouldn't make a habit of it but your car won't detonate. Hope that helps.
Last edited by Crabbers; Feb 12, 2015 at 04:01 PM.
Advanced
Joined: Jan 2015
Posts: 97
Likes: 0
My daughter drove our C5 on her permit--and the GTO on weekends
Never a problem with pre ignition--and no long term bad effects after 14 years owning the vette.
If circumstances dictate a tank or few of lower octane it is no problem--It just slows the cars down based on experience--YMMV.
Never a problem with pre ignition--and no long term bad effects after 14 years owning the vette.
If circumstances dictate a tank or few of lower octane it is no problem--It just slows the cars down based on experience--YMMV.
Burning Brakes
Joined: Jul 2000
Posts: 761
Likes: 0
From: Tucson AZ
Golly...I don't know what to do at the gas pump anymore!
I read the "covering our *** manual"....I mean "owners manual" regarding octane ratings.........just remember when you see the words, "can be used", "could be damaged", "may occur & may void" and the holy grail, "recommended"....just reach up and scratch your head, hope you don't go deaf so you can hear strange fuel related noises at 5 thousand RPM so sum hungry mechanic on the forum can make a boat payment on you fixing the engine cuzz he "knows" these words are clear, concise, irrevocable and final! Just relax, your engine isn't going to care and the GM lawyers can sleep at nite.
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Racer
Joined: Jan 2015
Posts: 388
Likes: 6
From: Far West
It amazes how many people do not answer the question. Some of you are just down right rude!
My question has NOTHING to do with the cost of the fuel, or my ability to pay for it.
I am asking whether after a year of real world use, has anyone had trouble running regular fuel?
New 2015 on the way, and if I get caught running a tank of regular fuel because my local station runs out - has this caused anyone any trouble?
My question has NOTHING to do with the cost of the fuel, or my ability to pay for it.
I am asking whether after a year of real world use, has anyone had trouble running regular fuel?
New 2015 on the way, and if I get caught running a tank of regular fuel because my local station runs out - has this caused anyone any trouble?
-- The engine has an 11.5:1 compression ratio. That higher than the current engine's 10.7:1 compression ratio. Despite the higher ratio, the new Corvette can run on regular unleaded fuel although premium fuel will be recommended.
Thread Starter
Burning Brakes
Joined: Jan 2005
Posts: 796
Likes: 444
From: Miami & Naples, FL
Unmodified C8 of the Year 2021 Finalist
when the new stingray engine was being introduced, one of the things gm touted, "the new corvette can run on regular unleaded fuel although premium fuel will be recommended".
http://autoweek.com/article/car-news...ck-uses-direct
http://autoweek.com/article/car-news...ck-uses-direct
Melting Slicks
Joined: Jul 2004
Posts: 2,216
Likes: 285
From: Ten Mile TN
Find it hard to believe some one would spend over 50K on a car, where it recommends 91 or higher and not use it, even if you can use 87.
Heck, 93 is all mine has seen.
Burning Brakes
Joined: Oct 2014
Posts: 762
Likes: 125
From: Houston TX
Both of My wife's Mercedes ML SUV & daughter's 3 Series cars with 6 cylinders "recommends" mid grade fuel with 91 octane.
Both of them has been using 87 octane reg gas for over 3 yrs now, with no problems with performance nor gas mileage.
But I'll stick with premium gas my C7 since I drive her a lot more agressively....
Both of them has been using 87 octane reg gas for over 3 yrs now, with no problems with performance nor gas mileage.
But I'll stick with premium gas my C7 since I drive her a lot more agressively....
Race Director
Joined: Dec 2007
Posts: 19,574
Likes: 167
From: Frederick, MD
So you spend a min of $55k new, probably closer to $70k on a brand new sports car and you want to put regular gas in it? Especially these days with the prices so low. $.30 a gallon isn't much so give up a fast food lunch per week and you'll be ok. It will be better for you and the car anyway.
In Utah 85 octane is regular so I don't think you want to use that if you every passed by here.
In Utah 85 octane is regular so I don't think you want to use that if you every passed by here.
Advanced
Joined: Sep 2014
Posts: 78
Likes: 6
Since I don't like running my C-7 below 1/2 tank, I put in 1/2 tank of 93, and on the next fill, I put in 1/2 tank of 87.. When mixed u have an octane rating of 90 average... This engine can only utilize with full advance 91 octane... Have never experienced any pinging even going up hill and on throttle ... Always park mine w/full tank as its not a daily driver.. Do this same procedure on all my high performance bikes and boat...
Drifting
Joined: Jan 2005
Posts: 1,942
Likes: 1,328
From: Houston Tx
Since I don't like running my C-7 below 1/2 tank, I put in 1/2 tank of 93, and on the next fill, I put in 1/2 tank of 87.. When mixed u have an octane rating of 90 average... This engine can only utilize with full advance 91 octane... Have never experienced any pinging even going up hill and on throttle ... Always park mine w/full tank as its not a daily driver.. Do this same procedure on all my high performance bikes and boat...
Advanced
Joined: Sep 2014
Posts: 78
Likes: 6
Your math is questionable. Looks to me like on the times you fill with 93, the resulting tank will be 91, while on the times you fill with 87, your tank will be 89. So you are constantly alternating between 89 and 91 in your tank. The knock sensors will theoretically cover you at 89, but just barely, and there’s always at least a bit of a lag as the knock sensor “catches up” with what’s really in the tank. If you doubt my math, consider that half at 89 plus half at 93 equals 91, and then on the next fillup, half at 91 plus half at 87 equals 89. Yes, over time, it averages out to be 90, but it gets to that average of 90 by tank to tank switching back and forth between 89 and 91.
Kind of go by what the knock vibration sensors are telling me.. My other car is a Shelby GT 350 which recommends 91 octane as well, but have never heard the marbles in the engine sounds in it either under hard accel..
Race Director
Joined: Dec 2007
Posts: 19,574
Likes: 167
From: Frederick, MD
A full tank of gas will cost you about $5 more for premium. If you are cruising all day then you probably won't have an issue with the regular gas and can probably fill it up if needed. However, I doubt you will every run into a problem of not being able to find 91 octane gas somewhere before your engine flames out. However the Corvette likes to climb hills at lower RPM (if you have an automatic). This puts stress on the motor somewhat. My intention was never to flame the OP but there are many other places in life where you can save about $5 a week.
All of our gas is like garbage anyway compared to German gas. 91 AKI is 95 RON in the rest of the world, that is regular gas in Germany with 100 RON being premium.
All of our gas is like garbage anyway compared to German gas. 91 AKI is 95 RON in the rest of the world, that is regular gas in Germany with 100 RON being premium.
Advanced
Joined: Sep 2014
Posts: 78
Likes: 6
A full tank of gas will cost you about $5 more for premium. If you are cruising all day then you probably won't have an issue with the regular gas and can probably fill it up if needed. However, I doubt you will every run into a problem of not being able to find 91 octane gas somewhere before your engine flames out. However the Corvette likes to climb hills at lower RPM (if you have an automatic). This puts stress on the motor somewhat. My intention was never to flame the OP but there are many other places in life where you can save about $5 a week.
All of our gas is like garbage anyway compared to German gas. 91 AKI is 95 RON in the rest of the world, that is regular gas in Germany with 100 RON being premium.
All of our gas is like garbage anyway compared to German gas. 91 AKI is 95 RON in the rest of the world, that is regular gas in Germany with 100 RON being premium.
In areas where 93 isn't prevalent, this blending doesn't work very well.. I broke in my 15 A8 Z-51 in on strictly 93 premium for about 1500 miles..
My mpg and drivability is identical as when I switched to the mixture..
The spark advance in the ECM doesnt do anything better with 93 than 91, and from 91 to 90 octane probably isn't even recognizable in the spark advance system. I thought I would see even a small amount of mpg loss, but its identical.. I drive the same route 3 days a week, and about the same speeds... Even the plugs look the same. With no sign of preignition, or sounds of it. I don't track my car, but do jump on it once in a while when an SS Camaro starts barking at a light, but all in all, it runs fine with the mix. I do run the recommended amount of Marvel Oil in my fuel since a kid, and it has additional benzene in it which is an octane improver.. Not much though, about 8 ounces per tankful.
Drifting
Joined: Jan 2005
Posts: 1,942
Likes: 1,328
From: Houston Tx
US gasoline on the whole is a bit lower octane because we make a much higher fraction of our fuel into gasoline, with much less of it going to diesel. A detailed discussion of why that affects octane would be a very long post, boring most to tears with technical jargon. But a short, layman’s version is that if you are trying to maximize gasoline yield, you have to keep all the gasoline range components in gasoline, you can’t afford to use some of the lower octane ones for other products. The reason for California being lower than the rest of the US is California state air pollution regulations. They very heavily restrict olefins in gasoline, and olefins are considerably higher octane than their corresponding saturates. So these things are not big conspiracies and do not represent selling “garbage”. It’s simply a case of situations being different in different places.
Drifting
Joined: Jan 2005
Posts: 1,942
Likes: 1,328
From: Houston Tx
Agree there is little or no penalty dropping from 93 to 91. But as I mentioned earlier, your strategy does not result in a further drop from 91 to 90, it is from 91 to 89. Every other tank, you are running what amounts to straight mid grade. That’s not disastrously bad. The knock sensors should catch it. But it is taking at least a bit of a chance. You may well get by with it, but I doubt that many would want to chance it.