Popular Mechanics - premium gasoline

[CELICA_XX]

I was reading in Popular Mechanics about buying gasoline and the difference in octane ratings.

Again, most of it is common knowledge... but they explain how the additives in premium gasoline cause it to burn more slowly and smoothly than regular. Your pistons get a "push" instead of the sharp blow that may occur under high loads with lower octane regular.

Even with the invention of knock sensors, wouldn't premium gas be a bit more gentle on the engine ?

 

[Lethal1ty17]

engines are designed to contain several thousand explosions per second, if there were serious implications of using non-premium gasoline because it was "less gentle" then i think we'd know by now.

its common sense, if the engine was designed for premium (i.e. high compression ratio) then run premium, if it wasnt designed for it (lower compression ratio) then premium can actually cause a performance hit. wont really hurt anything, just wont technically run as well as it should.

 

[CELICA_XX]

Originally Posted By: Lethal1ty17
its common sense, if the engine was designed for premium, then run premium


Yes, this was my belief.

The article just hinted to the fact that higher octane fuels would create a less aggressive explosion on the piston.

Which I thought might lead to less wear.

 

[Shannow]

Originally Posted By: CELICA_XX
... but they explain how the additives in premium gasoline cause it to burn more slowly and smoothly than regular. Your pistons get a "push" instead of the sharp blow that may occur under high loads with lower octane regular.


If they are explaining that premium burns slower, throw the article out, and write a letter to the editor complaining about it.

Both fuels burn at pretty close to the same rate.

The higher octane fuel is more resistant to igniting in areas other than the direct presence of a flame front or spark.

Up until the point that the regular can't handle the conditions of temperature and pressure in the chamber, there is no difference in the pressure characteristics of either.

 

[Lethal1ty17]

i wouldnt worry about explosions in my engine getting too violent, they are designed to contain explosions and harness that energy to drive the car, thats the whole purprose. if it was that large of a problem then im sure we'd know by now.

 

[mongo161]

IMO...If your vehicle is designed for regular gasoline...and the manufacturer suggests regular gasoline....then buying premium is throwing your money away.

Just use what works....and be happy.

 

[Oldwolf]

Only if the engine is pinging should you worry about violent combustion.

 

[Quest]

Originally Posted By: Shannow
Originally Posted By: CELICA_XX
... but they explain how the additives in premium gasoline cause it to burn more slowly and smoothly than regular. Your pistons get a "push" instead of the sharp blow that may occur under high loads with lower octane regular.


If they are explaining that premium burns slower, throw the article out, and write a letter to the editor complaining about it.

Both fuels burn at pretty close to the same rate.

The higher octane fuel is more resistant to igniting in areas other than the direct presence of a flame front or spark.

Up until the point that the regular can't handle the conditions of temperature and pressure in the chamber, there is no difference in the pressure characteristics of either.


Second that wholeheartedly!

Unfortunately, this misunderstanding of higher octane rating vs gasoline flame rate (flame propagation rate) has always been there out in the NA automobile community (claiming that higher octane rating automobile gas burns "slower" to that of automobile gas of lower octane rating) and it's been forever perpetuating as an urban legend.


Q.

for those who like to quickly disqualify my point please read my sentence (in brackets) carefully. for I'm talking about automobile gasoline here, not some high-test AV gasoline nor special custom blend for certain kinds of racing use.

 

[Audi Junkie]

The Astra specs 87 but runs way better on 91.


I think real octane need comes down to driving style. My Mom could probably drive a super car on regular. If I drove that same car, I'd need super.

 

[Shannow]

that's the really sad part of the life of a spark ignition engine.

99% of the time, you don't really don't need the octane that you do for 1% of the time.

But you can destroy an engine quickly in that 1%.

 

[SteveSRT8]

No modern gas engine is going to do anything but dial back the timing when filled with low quality/octane fuel.

They are completely unharmed by the experience. Most of them will not even ping.

 

[Oregoonian]

Originally Posted By: mongo161
IMO...If your vehicle is designed for regular gasoline...and the manufacturer suggests regular gasoline....then buying premium is throwing your money away.

Just use what works....and be happy.

+1
____________________________________
2003 Ford Focus SE (2.3L) / 87K
M1 5w20EP / OCI: 1 yr or 10K+/-
M1 EP Filter
Fuel: Regular

 

[mechtech2]

Originally Posted By: Shannow
Originally Posted By: CELICA_XX
... but they explain how the additives in premium gasoline cause it to burn more slowly and smoothly than regular. Your pistons get a "push" instead of the sharp blow that may occur under high loads with lower octane regular.


If they are explaining that premium burns slower, throw the article out, and write a letter to the editor complaining about it.

Both fuels burn at pretty close to the same rate.

The higher octane fuel is more resistant to igniting in areas other than the direct presence of a flame front or spark.

Up until the point that the regular can't handle the conditions of temperature and pressure in the chamber, there is no difference in the pressure characteristics of either.


Right. It is the INCEPTION of ignition, and resistance to self ignition that is delayed with premium fuels. A normal burn is of course slower than a fast BANG!
Unfortunately, the rather prestigious Popular Mechanic's is spewing old myths. Many will cling to their advice, though.

 

[Garak]

Originally Posted By: Audi Junkie
The Astra specs 87 but runs way better on 91.


I'd suspect a lot of German vehicles are like that. My Audi recommends 91, but only requires 87. It, of course, has a knock sensor. I run premium in it. I would suspect that in Europe, especially a decade or so ago, there would have been a wide range of different qualities of gasoline available.

Here, too, one has to be cautious. We all know the difference between a basic 87 at a no name gas station versus a top tier 91. Certainly, if it's a vehicle that only calls for 87 (not even recommending premium) and one puts in quality 87, there shouldn't be any noticeable difference.

I've also gotten bad premium from stations where they simply don't sell enough and it sits there forever.

 

[Quest]

Don't forget that part of the deal RE: most recently released cars can take on virtually any grades of gasoline has to do with the fact that (due to technical progress, computer control, etc.), cars these days no longer have to limit themselves RE: octane ratings.

Computerised ignition control, dynamically adjustable (computer controlled in a closed loop fashion) ignition timing throughout the entire operational range (from idling all the way to red-line), etc. coupled with knock sensors to monitor the timing (and immediately retards the ignition timing the moment it detects pre-ignition presence, in a fraction of a second), is what makes it possible nowadays.

Thats why even most computer-controlled cars that originally spec'ed for premium of 91 or more can still run with 87 octane rating gas (abeit less hp output) safely. It's all about the ability to dynamically adjusts it's ignition timing that we aren't able to back in the days of yore (or should I say distributor-based spark ignition systems).

My 2c's worth.

Q.

 

[Gary Allan]

One thing about this term used here "explosions". It's ideally a uniform flame front that migrates across the chamber in an integrated uniform manner. At some point in the process, you have an ever expanding flame front advancing into a decreasing volume of space. If it holds itself together, you get peak power out of it. Higher octane will allow it to stay looking like that alien fire storm on Independence Day. If it fractures ..can't remain integrated ..starts shooting off in a couple of angles.. you'll hear the sound of the colliding flame fronts. That's the knock you hear.


Think high potency "puff" with thermal content ..or maybe a ZIP file. You deliver it compressed in content, and let it unpack.


If "explosions" were routine, there would be a bunch of pistons with holes in them.

 

[countryboy9799]

If it calls for 87 and there are no pinging or other problems save your money and buy the regular gas. In a normal car dont worry about the explosions being more severe, it probably isnt that much different anyways. Less explosive power would mean less power in a regular car.
I want my car to last as long as I can and I worry more about driving it easier, changing oil regularly and buying cars that have a reputable history, thats what will insure having a car that will last 250K and more.
Back in my early days I had an 87 Bonneville that was redlined many times a day and always driven hard, oil was changed at 3000 miles and my gf at the time totaled it out at 210,000 miles. That engine would have easily made 350,000 miles.

 

[Garak]

Originally Posted By: Quest
Thats why even most computer-controlled cars that originally spec'ed for premium of 91 or more can still run with 87 octane rating gas (abeit less hp output) safely. It's all about the ability to dynamically adjusts it's ignition timing that we aren't able to back in the days of yore (or should I say distributor-based spark ignition systems).


That's quite right. Polaris snowmobiles, as an aside, started years ago (1996 I believe) with having a switch for premium versus regular. They still have some provision for that, if I recall correctly.

 

[GMBoy]

Engine design and controls have improved over time, for sure. Case in point - my '94 5.7 V8 (LT1) Corvette (in stock form) makes 300hp and requires 91 octane. Flash forward to 2008 and my CTS with the DI 3.6 V6 is making 304hp and GM only requires 87 octane.

I run what the OEM says to, anymore is a waste of money unless your car is so badly maintained that you need more octane Or, if you've you modified the car - you may need more octane. I've been trying to tell a friend for years that her 2005 CTS with the little 2.8V6 and all of 205hp does not need 93. But she thinks she is treating her car better... LOL!

 

[lexus114]

I hate when the manual states (which mine does) select 87 octane fuel. For increased performance,the use of 91 octane or higher is recommended.

Now I know this is simple to understand,but if you read into it too much,you can get a little confused.