Fuel Octane

parksah07 · Post by **parksah07** » 08 Nov 2004, 00:26

currently i see a ton of different octane ratings and a ton of different oppinions on it, some people say it doesnt help performance at all, some say it does,

im just wondering whats the difference between 87 octane to the 94 stuff, performance? better on engine? better for fuel filter?

besides the price difference heh

thanks again guys

Volvord · Post by **Volvord** » 09 Nov 2004, 19:53

This explains octane, directly from the oil company.
http://www.shell.ca/code/motoring/encyc ... ctane.html

parksah07 · Post by **parksah07** » 10 Nov 2004, 00:50

thank you, volvos 'anti knock' rating is 91 isnt it?? (91 octane)

ozzimark · Post by **ozzimark** » 21 Nov 2004, 17:26

i think my 740gle is supposed to run on 87. if not.. well it works fine on it. hehe

petershen1984 · Post by **petershen1984** » 02 Apr 2005, 08:29

If this is accurate as a rule of thumb, cars with compression ratios of over 10:1, or if the engine is turbocharged, then the premium grade is required, because this "compression" is what causes lower-graded fuel to ignite before actual spark.

Knocking/pre-ignition wastes power because, while the piston is being pushed up naturally in the cylinder, the preignition pushes the cylinder down before it reaches the top. Consequently, the piston is forced to "knock" on the sides of the cylinder walls, which makes the sound we hear typically when the engine is under a workload (climbing hills, with more passengers).

Black850 · Post by **Black850** » 17 Apr 2005, 13:45

I also read in a magzine, I think consumer reports, that newer cars will modify the timing according the fuel put in. So the performance will drop but the strain on the engine won't be as great.

J_Guynn · Post by **J_Guynn** » 29 Apr 2005, 07:48

petershen1984 wrote: Knocking/pre-ignition wastes power because, while the piston is being pushed up naturally in the cylinder, the preignition pushes the cylinder down before it reaches the top. Consequently, the piston is forced to "knock" on the sides of the cylinder walls, which makes the sound we hear typically when the engine is under a workload (climbing hills, with more passengers).

Knocking (detonation) and pre-ignition are two different and unrelated things. The result sounds the same but the damage caused by knocking is different than that caused by pre-ignition. Typically knocking breaks things (like rings or ring lands) while pre-ignition melts things (like spark plugs and piston crowns).

The pinging or knocking sound you hear is not physical contact between the piston and the cylinder wall (which would quickly result in a ruined piston) but the sound of the pressure wave from colliding flame fronts hitting the piston...yes the impact from that pressure spike is loud enough to be heard.

J_Guynn · Post by **J_Guynn** » 29 Apr 2005, 13:21

If you want a very indepth article about detonation and pre-ignition, follow the link below:

http://www.streetrodstuff.com/Articles/ ... /index.php

It's 8 pages long and technical...but well worth the read.

ppcgm · Post by **ppcgm** » 23 Aug 2007, 13:09

pump prices here are $2.40 for "regular" and $2.60 for "premium" ... I usually put in 15 gallons of this overpriced low grade ripoff excuse for fuel at the time ... so that's $36 for the cheapest stuff they have or $39 for the best available ... that's less than 10% difference and the car drives better, idles better and gives me that tiny little bit of peace of mind that I'm doing the best I can to keep my Volvo's engine healthy ... why would I save $3 and run 87 through my car ? and someone is going to have to explain to me why 89 costs as much more than 87 as 93 does over 89 ... is that new math or something ? ... did you know that when a nuclear device is detonated over sand it produces green glass that glows in the dark ? what a neat effect !

Klausc · Post by **Klausc** » 01 Oct 2007, 13:20

Because of the 2 knock sensors in our engines, most of us cannot tell when the engine requires a higher octane. But, if you keep track of gas mileage from tank to tank, and have a turbo, you will be able to determine which grade is best for your driving style.
When the engine management computer detects knock, the timing is retarded until the knock goes away. This is how cars "determine" what grade of gasoline you use.
If you have a turbo and occasionally use the turbo, the 89 octane will probably work. If you like to put your foot in it a lot, then 91+ is for you.

For those readers not in the USA, our octane ratings are different than yours. Our 91 rating is about the same as 98 in Europe.

Klaus