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There is only one station in town that has 93 octane gas . Recently even that station was out and I could only find regular unleaded. Any suggestions. This is my daily driver and my only automobile . Is lower (87 octane gas ) a problem .
You can probably get additive at an auto parts store to boost the octane during the shortage. But don't get it on the paint trying to get it in the tank.
Assuming that you have the base (ie, not supercharged) engine, 87 is ok. The knock sensors will retard the spark to protect the engine. There will be a slight loss of power, but the car has so much power to spare that it shouldn’t be a serious drawback. If you have the supercharged engine, risk of engine damage from 87 is higher, as the knock sensors can’t retard spark enough to prevent knock at full throttle in that engine. In either engine, if you do hear heavy knocking, ease off on the throttle until you can find some premium fuel.
I would not recommend an octane booster. They are either based on MMT or aniline, both of which are at least as risky as the risk of engine knock. In the case of MMT, it’s an organometallic, and the metallic part will poison your catalytic converters and foul your spark plugs. In the case of aniline, it’s highly corrosive and could damage fuel system components. Supporters of octane boosters say those risks are not very great. GM specifically mentions both of them in the owner’s manual as being high risk that could void the warranty. I’d believe a specific warning from GM before I’d believe chatter from an internet “expert”.
That's the best strategy. Keeping to round numbers for easy math, if you "top up" with 5 gallons of 87 octane on top of 10 gallons of 93 octane, you'll have 91 octane in the tank. It's a weighted average thing.
Please don't hate me because 1) I like easy math, especially early in the morning and 2) I really don't know the tank size on a C7.
Originally Posted by proexpert
You can probably get additive at an auto parts store to boost the octane during the shortage. But don't get it on the paint trying to get it in the tank.
Waste of money, and you're putting "mystery juice" in your fuel system. Is that a good idea?
If the "booster" specifies an octane rating for the juice in the bottle, maybe. If it specifies a mix ratio and resulting octane rating for the fuel, maybe. Most specify neither because the math is so bad you'd never buy it.
Again, it's a "weighted average" thing. If you add a pint (16 ounces, 1/8 gallon) of a liquid with an octane rating of 145 to 15 gallons of 87 octane gasoline, you're still short of 87.5 octane for the blend. The "octane booster" doesn't have an octane rating of 145, it's lower than that.
Originally Posted by hoganj
87 is fine. Read the owner's manual. I use it a lot, especially on long trips.
The PCM/ECM will detect knock and compensate for lower octane gas by reducing performance. If you've got knock to detect, you're already doing some potential damage to the engine. The knock sensors and electronics will step in to reduce/minimize the damage, but it's not completely eliminated.
I know it's a Corvette, and a C7 at that, but the best thing is, don't use full throttle or "maximum performance" if you know you've got 87 octane in the tank. At mild throttle openings, cylinder pressures are lowered enough that it won't knock/ping with 87 octane. The issues with low octane fuel are mostly at wide throttle openings, and especially at low RPMs with wide throttle openings. Tape a small piece of 2x4 to the back of the accelerator if you have to, but keep your foot out of it when you have 87 in the tank and you'll be fine.
Oh, and 87 is ideal for cross country trips on the cruise control. Often you'll get better fuel economy with 87 octane fuel. There's less oxygenates (ethanol, etc.), AKA "partially burned fuel" in the lower octane fuels, so theres more energy (BTU's per gallon) which gets better fuel economy.
Oh, and 87 is ideal for cross country trips on the cruise control. Often you'll get better fuel economy with 87 octane fuel. There's less oxygenates (ethanol, etc.), AKA "partially burned fuel" in the lower octane fuels, so theres more energy (BTU's per gallon) which gets better fuel economy.
That is just plain wrong - the higher the octane the more potential energy gasoline has. An engine designed with a compression ratio set to use 91 octane will be more efficient using 91 octane than 87 octane, because to use 87 octane it retards the timing which reduces efficiency.
An engine designed for 87 octane will not be able to release the added energy in 91 octane fuel, so there is no benefit to using it.
All E10 fuel is just that: 10% ethanol, it doesn't matter if it is 87, 89, 91, 93 or any other octane.
Both of the prior two posts are at least partially incorrect. Octane has nothing whatever to do with energy content. Octane is simply a measure of that fuel’s resistance to knock and detonation. The higher the octane rating, the less likely the fuel is to knock, so the higher the engine’s compression ratio can be without having to retard spark to control knock. It is the higher compression ratio without spark retard that gives engines designed for premium more power. The fuel itself does not contain more energy.
The biggest factor in energy content is ethanol content. Ethanol contains less energy than gas, so the more ethanol, the less mileage. Ethanol has no effect on engine power, just mileage. The second biggest factor in energy content is whether the fuel is summer or winter blend. Winter blend has more butane to raise vapor pressure for cold weather starts, and butane contains less energy. As with ethanol, that does not affect engine power, just mileage. After those two factors, it’s pretty much noise level. On average, regular contains a tiny smidgen more energy than premium, because it tends to have a bit more of the heavier, denser components that are lower octane but contain a bit more energy due to their higher density. But any given batch can go the other direction, and any such effects are extremely small.
- the higher the octane the more potential energy gasoline has.
Now that is just plain wrong.
All pure gasoline (pure hydrocarbons) has about the same energy density. It's about 114,500 BTU's per gallon. That's a function of the hydrogen and carbon in the molecules, and that's fairly constant regardless of octane rating.
Higher octane fuels require more energy (pressure, temperature, spark) to ignite and start combustion. That's a function of the arrangement of the carbon atoms in the various compounds in the gasoline. Straight chain molecules (know as paraffins) ignite fairly easily. Molecules with multipe forks and branches in the carbon structure (isomers like trimethyl-pentane) take more energy to ignite. Once you ignite the gasoline, you get the same energy (heat) out of it because there are the same number of carbon and hydrogen atoms to combine with oxygen.
Ethanol has only about 76,100 BTU's per gallon. There's less energy in a gallon of ethanol, so it won't push your car as far. It takes roughly a gallon and a half of pure ethanol to get the same energy as one gallon of pure gasoline.
The more ethanol in the blend, the more gallons of fuel you'll burn to go the same distance. NASCAR teams learned this lesson a few years back when they switched to a 15% ethanol blend (E-15). They had some fairly spectacular miscalculations, with cars coasting to the finish line out of fuel.
Originally Posted by LIStingray
All E10 fuel is just that: 10% ethanol, it doesn't matter if it is 87, 89, 91, 93 or any other octane.
Outside of certain jurisdictions where enviro-fascists have mandated 10% (minimum) ethanol in all gasoline based fuels, "gasoline" is a blend of up to 10% ethanol and 90% to 100% pure gasoline hydrocarbons. The label on the pump says "May contain up to 10% ethanol."
I've measured the ethanol content from various gas stations around North Georgia and Eastern Tennessee. Most 87 octane "regular" blends are under 5% ethanol around here. Typically around 3%, and some are actually "ethanol free" even though they don't advertise that. Premium blends (91 to 93 octane) are pretty much universally 10% ethanol around here. Pure gasoline has about 114,500 BTU's per gallon +/-, 10% ethanol blend will have about 111,000 BTU's per gallon +/-, and 3% ethanol blend will have about 113,000 BTU's per gallon +/-.
Assuming the same driver, vehicle, driving conditions and "driving style," miles per gallon (and tank range) will be proportional to those numbers. For example (using easy math numbers), if you average 22.2 mpg with premium (10% ethanol), you'll probably get about 22.6 mpg with regular (3% ethanol blend), or 22.9 mpg with "ethanol free" gasoline.
Void where prohibited by law.
Last edited by C6_Racer_X; 09-21-2017 at 09:04 AM.
I have a LT4 engine so 87 isn't an option but the manual wording for the LT1 makes it clear that 87 isn't a preferred choice and the owner has to exercise due caution in operation to check for and avoid knocking. I wouldn't use it in a LT1 unless there is no other choice and I would make sure to avoid any high load operation on the engine.
GM recommends 87 octane for the 3.6L in my Cadillac ATS (11.5 to 1 CR) but light knocking is noticeable at lower engine speed under load and I switched it to 89 which is sufficient to keep it quiet.
I run 93 most of the year in my Z06 except right before winter storage I will run a few tanks of 91 through it because that is the highest octane ethanol free available in my area. Ethanol itself has a very high octane rating thus its popularity in creating high octane blends and the difficulty of finding ethanol free 93 in many areas.
I've measured the ethanol content from various gas stations around North Georgia and Eastern Tennessee. Most 87 octane "regular" blends are under 5% ethanol around here. Typically around 3%, and some are actually "ethanol free" even though they don't advertise that. Premium blends (91 to 93 octane) are pretty much universally 10% ethanol around here.
Thanks, I have wondered if anyone had actually measured the ethanol content. Anecdotally that fits well with my experience recently. My local station has both E10 93 and ethanol-free 91 (or 92, it's a point or 2 lower but I don't remember which right now). Mileage difference between the 2 types is so close as to be in the noise, which has led me to believe that the E10 fuel doesn't have anywhere close to 10% ethanol.
And the price difference between the two types is only $0.10/gallon, about 3-4%.
87 is fine. Read the owner's manual. I use it a lot, especially on long trips.
Ok, what am i missing?
My manual very clearly states
Section 9-52 "Use premium unleaded gasoline
meeting ASTM specification D4814
with a posted octane rating of 91 or
higher. If the octane is less than 91, damage to the engine may occur
and may void the vehicle warranty.
If heavy knocking is heard when
using gasoline rated at 91 octane or
higher, the engine needs service.
"
Ok, what am i missing?
My manual very clearly states
Section 9-52 "Use premium unleaded gasoline
meeting ASTM specification D4814
with a posted octane rating of 91 or
higher. If the octane is less than 91, damage to the engine may occur
and may void the vehicle warranty.
If heavy knocking is heard when
using gasoline rated at 91 octane or
higher, the engine needs service.
"
The 2015 owners manual also states "Regular unleaded gasoline rated at 87 octane or higher can be used, but acceleration and fuel economy will be reduced, and an audible knocking noise may be heard. If this occurs, use a gasoline rated at 91 octane or higher as soon as possible."
The 2015 owners manual also states "Regular unleaded gasoline rated at 87 octane or higher can be used, but acceleration and fuel economy will be reduced, and an audible knocking noise may be heard. If this occurs, use a gasoline rated at 91 octane or higher as soon as possible."
Oh wow! They changed the manual from 2014 to 2015! Huh, how bout that. I'm still not sure Im brave enough to do 87.
My caddy manual does read like what you posted. huge difference in performance tho. Not at all subtle.
I swear by Race Gas concentrate. It's what I use on my twin-turbo big block dyno mule, so it should be good enough to keep 87 happy during the shortage:
Oh, and 87 is ideal for cross country trips on the cruise control. Often you'll get better fuel economy with 87 octane fuel. There's less oxygenates (ethanol, etc.), AKA "partially burned fuel" in the lower octane fuels, so theres more energy (BTU's per gallon) which gets better fuel economy.
It kinda makes sense if you keep the revs high enough to avoid lugging, or if you have an automatic that will shift up under load. In my M7, I usually don't downshift for non-aggressive highway passing -- stay in gear, and just press a little harder on the gas gets the job done, esp on interstates where there's always plenty of time to pass.
However, in normal city/hwy mixed driving, when I've experimented with reg fuel, I'll see a 1-2 MPG *drop* when I use 87 octane instead of 91 in my manual transmission car, mostly negating any savings from using the cheaper grade.
When the engine retards the timing to accommodate the lower octane, it isn't running as efficiently, thus lower MPG.
Yes, every locale is different and one can only use what's available within a reasonable distance. Seems GM prepared for this in "allowing" 87. Such are the breaks.
Btw, for those old cars not amenable to any alcohol there is a Website that give "corn" free stations all over the country. Sometimes one finds a local source where one never knew it exists. Too bad no such Websites seem to exist for 93 availability.
09-21-2017, 02:45 AM
Premium gas shortage
