Is there any advantage to running premium?

[Clevy]

Wildly engine specific. If the engine's ecu will compensate with more power then in theory it would take less fuel to achieve the same mileage if the operator compensates for this by using less pedal,or if the engines compression ratio is high enough to require its use then of course use premium but if the ecu can't tell or the compression ratio is low enough to use regular then there really isn't any point in paying more for fuel.
Here premium is pure gas with no ethanol. That alone is reason enough for me to use it. I get better mileage because there isn't any ethanol but if our premium was ethanol polluted I wouldn't use it.

 

[webfors]

Originally Posted By: Rand
In the summer or when towing I use premium or fill up with half a tank of premium.

In my opinion my forester pulls timing on regular.

not very noticeable unless I'm loaded down or towing.

Some stations here cost 40cents for premium some are 20cents(extra)

I'll throw in half a tank of premium before a long towing trip.
93octane. Seems to make a noticeable improvement. Esp. trying to accelerate at 2500-3000rpm towing.. up an expressway ramp.

8gallon x20cent = 1.60$ =worth it to me. YMMV


I put 91/premium in the forester for this reason. It's not butt dyno science with data logging via a tatrix openport 2.0 interface to confirm timing being pulled with regular on the ej25. There was a lengthy thread on sf dot org about persistent pinging with pzev foresters that were cured with premium gas. Is the extra costs recouped through better mpg?? some say yes, others are more sceptical. Avoiding knock/detonation is my motivator and my mechanic said he's never seen such clean plugs when he changed them

 

[webfors]

Originally Posted By: 440Magnum
Will this whole "burn rate" myth NEVER die??

Its got zero to do with flame speed. Its got everything do do with ability to resist igniting without a spark, which is what can happen when high compression occurs with a still-glowing bit of carbon (or spark plug electrode, or whatever) in the combustion chamber. It also is the ability to resist igniting at a point far away from the spark source due to the sudden jump in pressure when the flame front begins at the spark source, which causes an audible ping but is generally less damaging than ignition prior to any spark at all. The igniting far from the spark source has been reduced a lot in modern engine designs by the shape of combustion chamber used. "Quench" areas and similar features.

If the engine has sufficiently low MECHANICAL compression (set by the bore/stroke and combustion chamber size) so that it can achieve full programmed timing advance without pre-ignition or detonation on regular fuel... then premium has NO advantage. If the compression is high enough (or high pressure is achieved with forced induction) so that pre-ignition or detonation can occur before full timing advance is reached on regular, then premium allows the computer to reach full advance and thus produce more power.


^ This

 

[ziggy]

I was talking about this other day with assitant manager where i work. we had both been told years and years ago, by our fathers, who learned from the local mobil gas station mechanic, its good once a month, too run 93 octane, as long as the car has a knock sensor. it has more detergency, and is a cleaner cleaned up gas. 87 tends to be dirtier. that way, you dont fall into the spending of money of botttles of detergency save some $$$$>
cant say thats true or not...

 

[ziggy]

of course, this was told too me by my fatherk, from his mechinc at the time, down the street, mobil station, when i was 17/18 that was 1992-93.

 

[Garak]

Yes, some retailers do advertise the enhanced detergency of their premium offerings.

 

[Shannow]

Originally Posted By: nitehawk55
Well to me detonating or exploding VS a controlled burn = a difference in how the fuel ignites , burns....whatever .


That'll learn science for trying to describe how the world around us works.

 

[Wolf359]

Originally Posted By: ziggy
I was talking about this other day with assitant manager where i work. we had both been told years and years ago, by our fathers, who learned from the local mobil gas station mechanic, its good once a month, too run 93 octane, as long as the car has a knock sensor. it has more detergency, and is a cleaner cleaned up gas. 87 tends to be dirtier. that way, you dont fall into the spending of money of botttles of detergency save some $$$$>
cant say thats true or not...


Probably not. Never ran that stuff in my car, regular all time time up to 185k with no detergents. Still running. Actually never did any additives in the 80 and 90's, but the previous car did knock a little in the summer heat so I used to do plus once in a while in the heat. Lots of things that were true before aren't now such as 3k oil changes.

 

[nleksan]

Meh, pushing 14.5psi of boost in a motor with 11.3:1 SCR, I'll stick with my 93AKI fuel or higher, thankyouverymuch!


Basically, Forced Induction and/or High Compression motors either BENEFIT GREATLY FROM OR REQUIRE the equivalent of 96-98RON fuel, aka 93"octane"(AKI) fuel.

I've even dyno'd my 328Ci (that's with a built bottom to top motor, modified and intercooled Lyshlom 2.5L twin-screw blower, etc) to compare the E10 and No-Corn 93oct, running the same exact custom 93oct tune for the runs.
Car pulled timing with just 10% ethanol, and it was down about 30lb-ft of torque from the get, and peaked below 400rwhp, while running pure 93AKI gasoline w/o any ethanol gave the numbers in my signature.
Fill it with 100oct, press the button for 100oct tune (have 91, 93, 100, 105, and 110oct tunes as track-to-track varies) and having swapped SC belt and pulley for 18.5 or 20psi one, and that's 399-417rwtq from just 1850rpm all the way through 6975rpm!


SO YES, OCTANE (AKI) MATTERS!

I've seen BMW motors whose anti-knock sensors were actually dead from OVER-USE due to people thinking "Oh gee, I'll buy a brand new $60K+ car and cheap out with some 87oct gas! BRILLIANT!"....

*SIGH*

 

[shovel]

Originally Posted By: Clevy
Wildly engine specific.


This right here.

As an example, Chrysler's 4.7V8 was available for some time in 2 "flavors" at the same time - a standard and a high output version. Same engine overall, but the HO version had a slightly tighter compression ratio (different heads and pistons), different computer firmware - but another important distinction was the standard engine had no knock sensors and the HO engine had one on each head. Both engines were rated to operate on 87 octane at sea level, but the HO version would get dramatically better fuel efficiency and produce more horsepower if fed a steady diet of high octane fuel. Since the engine had knock sensors it could continually advance the ignition timing until the engine would knock, then bring it back to just below knocking. The standard engine lacked this capability so no meaningful difference was possible between low and high octane fuels.