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Comments
for years i drove LG4/305-TPI/LT1/LS1 Z28s through new england winters without traction control - and during cold weather i'd use 87 octane in those as "poor mans traction control", just to reduce the torque off-the-line a bit. the LT1/LS1 Z28 engines pinged objectionably if i tried that in summer however.
I can. Even when loafing along (in fact, especially when loafing along), fuel economy is dramatically improved by advancing the spark timing. The higher the octane the fuel is, the further the spark can be advanced without the risk of detonation. It sounds to me like the GTO engine does its level best to keep the engine on that most efficient "Ragged edge of disaster", meaning, just a knife edge shy of detonation.
Best Regards,
Shipo
The simple truth is that the further the ignition timing is advanced (shy of detonation), the better the fuel economy an engine will return. Why? The primary reason is thermal efficiency, retard the timing, the peak combustion temperature (and peak cylinder pressure) drops, advance the timing and the peak combustion temperature (and pressure) rises. The more heat extracted from the fuel, the more work the engine is capable of performing for any given amount of fuel.
Best Regards,
Shipo
The result might be different if this is a Winter season.
My Jetta required min. 91 Octane. But its more time consuming in pumping the gas as most gas stations don't have 91 octane gas, I have to mix it up myself. I suggest you to use 91 octane to save some money.
Anyway, go ahead and fill up at Hess. The only difference you'll notice is the extra weight in your wallet.
Best Regards,
Shipo
i'll try to remember to read the exact text and will post more later if that's not accurate.
i know the inside of fuel door just says "premium fuel recommended".
does the owners manual of *any* USA car recommend gasoline octane *larger* than 91? !?
i agree that there is zero benefit to using anything more than 87 octane in a car designed for 87.
the whole discussion is less important now that the percentage difference between low-octane gas and higher-octane gas is so much less than it was when gasoline was $1/gallon. there was a 20% difference back then between regular & premium. now there's a 6% difference.
I guess what I was driving at is the common misconception that premium fuel is some kind of "doggie treat" for your car :P
Absolutely, positively no argument from me. I thought we were discussing the GTO which per a recent post requires 91 octane or greater, not a car that carries a recommendation of 87.
With your comments in mind, I'm thinking that in theory at least, it is possible to design a normally aspirated engine specifically for 87 octane, and then design the ignition system to be able to nominally take advantage of a higher octane fuel. That having been said, in reality my bet is that advancing the timing on such a car far enough to take advantage of fuels beyond say 89 octane is probably not going to happen.
Best Regards,
Shipo
Best Regards,
Shipo
Best Regards,
Shipo
my pzev focus has a manual transmission, no tach, and an upshift light(flashback to the 80's).
one time i filled up with 93 octane. got my worst mileage ever, 24.9 average for the tank, and the upshift light never came on. for the life of the car i have averaged 28.9 mpg.
my explorer seems to run quieter on high test, but the mileage in not necessarily better, except when using winter gas in a cold snap.
In the case of the Focus, there is no surprise that your mileage went into the dumper, Premium fuel simply isn't volatile enough for that engine.
As for your Explorer, unless your engine is heavily carboned up on the inside of the combustion chambers, Premium gasoline shouldn’t make it run smoother at all. In fact, due to the effectively cooler burn that results from high octane fuel and a low compression engine, all you are doing is accelerating the process of carboning up the combustion chambers. Once enough carbon builds up, then "Hot Spots" can occur, and when they do, then you really will need Premium just to keep the engine from running in a constant state of detonation.
Best Regards,
Shipo
with the explorer v8/auto/towing pkg, it seems like the transmission got out of sync with the change in the operaion of the engine. back to regular gas, everything is as was before.
what do you think about switching brands of gas because they have different formulations?
Regarding different formulations, logistically speaking I just don't see how one brand can actually sell different gasoline than the next due to refining and transportation issues as well as various efforts at standardization such as the "Top-Tier" gasoline program.
I'm sure this wasn't much help but there you have it. :-/
Best Regards,
Shipo
Vettever
Go figure....
Best Regards,
Shipo
The only correct answer here is, "It depends."
If any given engine is optimized for 91 octane but has ignition control electronics that allow it to retard the spark event for more volatile fuels (lower octane) and/or advance the spark event for less volatile fuels (higher octane), then the "Minimum Octane" in the manual might could well be 87. That having been said, that same engine will lose both performance and economy when anything less than 91 is being used.
The flip side of course is when any given engine is optimized for any given octane rating and then a higher octane fuel is used. In this scenario, performance and fuel economy will suffer if the engine isn't able to advance the spark event sufficiently to start the fuel burn early enough. If, however, the engine can advance the timing, economy and power may actually improve slightly, of course, not as much as an engine optimized to burn said higher octane fuel.
Best Regards,
Shipo
I had a VR6 in my 1995 Passat and on that engine I don't remember it being at all sensitive to fuel above 91 or 92 octane.
Sorry I can't be more help than that.
Best Regards,
Shipo
I live in an area where the gas stations are dominated by the local convenience stores, Rutter's, Sheetz, Tom's, etc. Reading a few forums, the discussion of top tiers gasoline providers popped up. It dawned on me that none of these providers are in my area (South Central PA) or are they? Is there a way to find out who provides the gas for these stations? Obviously Rutter's and Sheetz don't own refineries and must buy from someone.
Many people get upset or can not understand why the GAS mileage of same vehicles differs so much. It is quite simple and it is not what most people talk about. Yes how you drive has a lot to do with it but the one main reason that mileage differs on two like vehicles is ALTITUDE.
ALTITUDE will determine how lean or rich your car will run. Higher altitude will provide better gas mileage if your car is tuned properly for the higher altitude.
Here is a simple explanation of what I mean.
With altitude, air density decreases, so a computer controlled fuel injection system will automatically decrease the fuel in the mixture to match the air density. Thus all the electronic sensors needed to keep the motor running correctly. You will find that horsepower will decrease, but mileage will actually increase.
This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the fuel mixture after reaching cruise altitude, you leave the fuel mixture at full-rich while climbing.
I hope this help explain why gas mileage is so different from so many people. The higher the altitude the better mileage. So people in Denver get better mileage then people in Death Valley California.
If you need a better explanation your local mechanic can also explain this to you.
Cheers!
2014 Malibu 2LT, 2015 Cruze 2LT,
In thicker or more dense air you need a more rich fuel mixture increasing the power output to move you 1 mile thus burning more fuel.
Even though the car is doing the same speed and distance the output of fuel needed is greater or lesser depending on the fuel mix based on air density. You can not get around it.
What is the difference in air resistance at 900 feet altitude compared to 0 feet?
2014 Malibu 2LT, 2015 Cruze 2LT,
also, it explains why I've been seeing such lousy mpg while driving in the Marianas Trench.
Ummm, no. Modern fuel injected cars measure the weight of the air coming into the engine and provide the exact same amount of fuel per pound of air at all altitudes and all temperatures and all humidities. Fuel economy as measured by the conventional Brake Specific Fuel Consumption (BSFC) measurement won't change one iota regardless of any of the above "Density Altitude" factors.
"This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the fuel mixture after reaching cruise altitude, you leave the fuel mixture at full-rich while climbing."
Ummm, no again. GA aircraft can extend their range at altitude simply because air resistance against the airframe is lower at altitude. Said another way, I take out say a Skylane and set it up as lean as possible to cruise at 100 knots in level flight at sea-level, and then measure the hourly fuel flow. I then take that plane up to say 17,000 feet and lean out to the exact same hourly fuel flow setting, that plane will have a true airspeed of 137 knots. That, and only that, is why aircraft get better economy at altitude.
FWIW, I've seen anecdotal evidence that suggests that cars will see some gains in economy at altitude (but no where near as dramatic as with aircraft due to the rolling friction of the wheels), especially turbo-charged cars.
Best Regards,
Shipo
That said, stoichiometric is stoichiometric is stoichiometric. Given the proper air and fuel ratio, the mixture will burn exactly the same regardless of whether the aircraft is at a density altitude of sea-level or 17,000 feet. ;-)
Best Regards,
Shipo
Best Regards,
Shipo
Best Regards,
Shipo
Thank You
Best Regards,
Shipo
2014 Malibu 2LT, 2015 Cruze 2LT,