Gasoline types: which one is better

Munacra

At the gas station, they have the regular, the one in the middle, and the premium one. I know they differ in octane levels, and that's the reason why the premium one is pricier. However, what I don't get is, does it in fact make your car run longer, and is the added mileage worth those extra cents?
Would that make the premium cheaper by comparison?

How much better is that premium gasoline, or should I just stuck with the cheapest one?

powerss

What kind of car do you have?

I'm going to take a wild guess that it is not exotic, turbocharged, supercharged, etc.

If it isnt, and it's four cyl, use regular. You gain NOTHING.

Munacra

Duly noted, but in that case, what does the premium do then? Like an added boost to the whatever makes it run?

I'm afraid cars aren't my forte.

powerss

That "octane rating" can be simplified to "how hard this gasoline is to ignite"

Now you're thinking "lower should be better! My gas should explode easily!"

Well, sorta. In a high-performance engine, with a high compression ratio (inside the cylinder) or that has say, a turbocharger (takes exhaust gases, spins a turbine, pressurizes intake gases [air] going into the engine) that means the gasoline is subject to higher temperatures and forces, meaning that with a low octane gasoline, the gas is more likely to pre-ignite (knock).

Pre-ignition is bad, you lose MPG, power, and the engine has to cut back on timing.

Anyway, with something like a Honda Civic, all you need is regular. Not exactly a speed demon, it doesn't have a turbocharger or a rediculously fast igniton cycle or anything.

However, the higher octane gases at places like Shell, 76, Chevron (name brand) also have detergents and additives (ProPower, Techron) that help keep your engine clean. They do work, trust me.

You dont get that in the base 87, though. The fix? Get a bottle of techron and add it to your gas tank once a month. It's like 3.49, add it on Empty and then fill up. It's worth it.

On my car, which has a Turbocharger, I need to use premium and I STILL add Seafoam (an additive) once in awhile.

Be happy you save some cash every fillup

Munacra

Ahhh, I think I get it.

I'm assuming the bottle of techron I could find at pepboys, right?

Thanks for the explanation, I just kept thinking that it added more miles or something. :P

powerss

Yep, Pep-Boys. Costco sells them in a small box at a big savings.

ViolentChemistry

Run the grade of fuel your car is built to run on. i.e; whatever it tells you to run in the manual. You shouldn't go changing shit up at random pretending you know what difference it makes, most modern cars will automatically de-tune for lower grade fuels but not all of them, and I doubt any are going to tune themselves up automatically to get the benefits of higher grade fuel.

That said, the number of cylinders has exactly jack shit to do with what kind of fuel you should be running.

Drakmathus

it should be noted that even though cars will adjust for the lower grade fuel it is very hard on the engine and if done continually you can expect the life of your engine to be cut in half or worse.

tsmvengy

Yeah, for most cars the lowest octane is fine. Back when I was in high school and driving all the time, I used to do some gas mileage vs price calculations. It came out that I was getting pretty much exactly the same price per mile with 87 octane as 89 octane - I got a slight mileage boost with 89 octane so I went with that (burning less gas is good).

So what I would say is premium is never worth it unless you have a car that needs it - check the manual. You might get better gas mileage with 89 over 87.

ViolentChemistry

Drakmathus wrote:

it should be noted that even though cars will adjust for the lower grade fuel it is very hard on the engine and if done continually you can expect the life of your engine to be cut in half or worse.

Hence "run whatever the manual tells you to". Don't go picking a number out of your ass based on random irrelevant shit like number of cylinders.

blincoln

powerss wrote:

However, the higher octane gases at places like Shell, 76, Chevron (name brand) also have detergents and additives (ProPower, Techron) that help keep your engine clean.

In the US, all grades of gasoline have those additives, because it's required by law.

variant

powerss wrote:

What kind of car do you have?

I'm going to take a wild guess that it is not exotic, turbocharged, supercharged, etc.

If it isnt, and it's four cyl, use regular. You gain NOTHING.

something my dad always says..." if you have a four cylinder and you're constantly over 5k rpms, you'd be better off using premium."

EggyToast

If your 4 cylinder is regularly over 4-5k rpm, that means you have a manual transmission (or your automatic transmission should be taken into the shop).

To me, having a manual transmission and running it like that doesn't mean you should get higher octane gas. It means you should learn how to drive a manual transmission.

ViolentChemistry is really the best advice for pretty much everything regarding your car. How frequently should you change the oil? look in the manual. What about other fluids? Same thing. Spark plugs? Hey, it's in the manual! The manufacturers run and beat up these cars far more than an individual, and know what you should and shouldn't do to them.

There are things that break or work incorrectly that aren't covered in the manual, such as the spark plug cables wearing out or changing your oil more frequently if you do 90% of your driving in the city (in which case it's usually between 3k and 5k).

*My* dad told me that the one thing you need to remember with cars is that basic maintenance will take care of most of what you need to do with a car, and things like leaded fuel and high octane are really just specialty things, more of a "curse" for owning a car that needs them, rather than an optional bonus for regular cars.

variant

It's not a matter of know how to drive, its just that alot of 4 cylinder cars will run in high rpms in the last gear, such as mine, I drive mostly on the freeway at about 80mph, so I'm always at 4k rpms...

I was told this a while ago, so I dont quite remeber exactly why but, I do recall him saying that it applied more to hondas as their engines usually have a higher compression ratio, so I suppose it has something to with that?

Im not trying to mis-educate, rather, confirming what I've perceived.

redimpulse

Here's a quick thought for ya: What's the price difference between regular and mid-grade? With most small-medium cars, the difference in price for a full fill-up is pretty negligible; around $2.00 or so.

powerss had the processes for octane down pretty pat. I run 85 in my focus. It gets me along well enough. However in my Impala (3.8 V6, 9.5:1 compression) I have to run 87 or better or like powerss said: KNOCK. KNOCK is bad. It will kill your car. KNOCK RETARD, a 'failsafe' feature used on most any vehicle these days, isn't much better either. If you're experiencing any knock, it's better to just fill up with a higher octane fuel. Higher octane isn't going to net you any more fuel economy, or any more power, or anything else like that. But it will save your engine from knock.

edit t variant: most N/A cars have a compression ratio of around 9.0-10.0:1. This is a standard put in place so people don't get confused about, say, fuel choices. Turbo/Supercharged vehicles will generally have an idle compression of about 8.5:1. But once the turbo/super kicks in, that can be boosted to upwards of 11.5:1. This is where the higher octane comes into play: It combusts at a much higher compression, allowing the pistons to reach full extension. A Honda N/A engine is really no different than a Toyota, or GM, or DC or whathaveyou.

ViolentChemistry

I'd like to stop seeing fucking stupid generalizations in this thread. If you're running a four-cylinder constantly above 4k, you should be running whatever grade of fuel the manual tells you to and potentially re-evaluate your shift-points (some engines are built to run that high though). If you're driving a turbocharged/supercharged engine, you should be running whatever grade of fuel the manual tells you to. If you're driving a Honda 4 cylinder, you should be running whatever grade of fuel the manual tells you to (even if the manual tells you 92 when a Focus wants 87 or whatever). Also, not all engines are the same, not all engines with the same number of cylinders are the same, and not all engines with the same mode of aspiration are the same. Some Honda 4-cylinder engines have very high compression, and the manuals in those cars will tell you to use a higher octane-rating gasoline than the manuals for the Honda 4-cylinders that run at lower compressions.

If you didn't build the engine, do what the people that did build it tell you to do.

JWFokker

Wikipedia wrote:

The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is mostly false—engines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal.

Using high octane fuel for an engine makes a difference when the engine is producing its maximum power. This will occur when the intake manifold has no air restriction and is running at minimum vacuum. Depending on the engine design, this particular circumstance can be anywhere along the RPM range, but is usually easy to pin-point if you can examine a print-out of the power-output (torque values) of an engine. On a typical high-rev'ving motorcycle engine, for example, the maximum power occurs at a point where the movements of the intake and exhaust valves are timed in such a way to maximize the compression loading of the cylinder; although the cylinder is already rising at the time the intake valve closes, the forward speed of the charge coming into the cylinder is high enough to continue to load the air-fuel mixture in.

When this occurs, if a fuel with below recommended octane is used, then the engine will knock. Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark. Here is a white paper that gives an example: [4] . In this example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load then the difference in octane will have even less effect. The example cited does not indicate at what elevation the test is being conducted or what the barometric pressure is. For each 1000 feet of altitude the atmospheric pressure will drop by a little less than 1 inHg (11 kPa/km). An engine that might require 93 octane at sea level may perform at maximum on a fuel rated at 91 octane if the elevation is over, say, 1000 feet.

blincoln

redimpulse wrote:

What's the price difference between regular and mid-grade? With most small-medium cars, the difference in price for a full fill-up is pretty negligible; around $2.00 or so.

That $2 adds up pretty quickly, depending on how much you drive and your car's fuel economy. Especially since in my experience the "it's only $2" mindset doesn't just apply to one type of purchase, but most or all of them.

Using higher-octane gas when it isn't necessary is throwing your money into the gas station's wishing well.

ViolentChemistry is right. Read the manual. Don't use higher octane gas unless you need to or you like giving away your money.

Munacra

I looked in the manual, and they did not specify what kind of gas was needed or anything of the kind.

However, it is a little cavalier, and seeing from everyone's thoughts, I'll stick with the regular one, instead of spending the premium one.

redimpulse

Cavalier? Then yeah, you're quite fine with regular.

But watch out for your fuel injectors (if it's a 98-2005). They can be finicky; you may want to run some injector cleaner through from time to time, say, every other oil change or so.

Ginzue

Uh oh...
I drive a 97 Volvo SMS T-5 high compression turbo. I recently had a fully rebuilt engine put in it, last week. I've never used anything other than regular. Should I be using premium?

Gas is EXPENSIVE for me, I live on a island, so its 4.00 or so a gallon for the good stuff.

Sorry to derail, but I'm a bit worried if I should use the good gas or not.

redimpulse

Well, as ViolentChemistry so colorfully put it above, you should read the manual and see what it says about the fuel grade.

But the general rule of thumb is that if your engine is forced induction, you should probably be using higher octane gas to help with the higher compression.

Parroteer

variant wrote:

It's not a matter of know how to drive, its just that alot of 4 cylinder cars will run in high rpms in the last gear, such as mine, I drive mostly on the freeway at about 80mph, so I'm always at 4k rpms...

I was told this a while ago, so I dont quite remeber exactly why but, I do recall him saying that it applied more to hondas as their engines usually have a higher compression ratio, so I suppose it has something to with that?

Im not trying to mis-educate, rather, confirming what I've perceived.

Well, true, but in my protege, I still don't go above 4200 or so when travelling at about 80 mph. I'd say going over 4k rpm should be relatively rare, and a total no-no in cities(except for the occasional flexing of the engine).

ViolentChemistry

Parroteer wrote:

variant wrote:

It's not a matter of know how to drive, its just that alot of 4 cylinder cars will run in high rpms in the last gear, such as mine, I drive mostly on the freeway at about 80mph, so I'm always at 4k rpms...

I was told this a while ago, so I dont quite remeber exactly why but, I do recall him saying that it applied more to hondas as their engines usually have a higher compression ratio, so I suppose it has something to with that?

Im not trying to mis-educate, rather, confirming what I've perceived.

Well, true, but in my protege, I still don't go above 4200 or so when travelling at about 80 mph. I'd say going over 4k rpm should be relatively rare, and a total no-no in cities(except for the occasional flexing of the engine).

*shrug* Depends on the engine. There are a bunch of engines out there that are built to spend a lot of time in the 3-5k range, the first year of S2000s in particular are quite happy to rev higher than that, even, and if you don't rev them high they don't move all that well. Although the S2000's redline isn't 7000, as it is on most DOHC 4-cylinder cars. You can build an engine to reliably rev high, you just have to have that intent in mind when you design it, and you're going to have better luck designing a small engine that way than a large one (.5mv^2 and all that). You probably don't want to do it without DOHC, valve-float blows. Also, rotaries.

But I wouldn't trust a Cavalier engine for that kind of use.

blincoln

If your manufacturer's manual doesn't list a recommended octane rating, you can pick up the Haynes or Chilton aftermarket maintenance/service manual which should. They're well worth having around for other purposes anyway.

TrippyDK

For years my dad put good ol' 89 octane premium into his jeep, thinking he was taking care of it. One day this good jeep shut down on itself. The culprit? It was the too high octane fucking up the engine with gunk or something like that.

Stick to whats you cars tuned for. Its cheaper in both the short and long run.

Regina Fong

The owners manual on my vehicle warns me not to use anything higher than regular, that it can damage the engine.

JWFokker

TrippyDK wrote:

For years my dad put good ol' 89 octane premium into his jeep, thinking he was taking care of it. One day this good jeep shut down on itself. The culprit? It was the too high octane fucking up the engine with gunk or something like that.

Stick to whats you cars tuned for. Its cheaper in both the short and long run.

That's just completely wrong.

redimpulse

TrippyDK wrote:

For years my dad put good ol' 89 octane premium into his jeep, thinking he was taking care of it. One day this good jeep shut down on itself. The culprit? It was the too high octane fucking up the engine with gunk or something like that.

Stick to whats you cars tuned for. Its cheaper in both the short and long run.

This is true. If your engine's ignition system is inherently weak, I.E. tuned for regular fuel and light-normal driving, then the spark won't necessarily be strong enough to burn higher-octane fuels. In this case, it's not knock that'll kill your car, it's (as stated above) unburnt mixture (or gunk). Unburnt fuel is just as bad for your car. It can screw up your oxygen sensors, your catalytic converter and other emissions-necessary components.