Octane Levels, Over 91

[ToplessFC3Sman]

ummm, emagdnim, a quick correction... The mass of the air/gas mixture does not change, because the number of particles doesnt change. Its the volume of it that changes. When the piston is at TDC, the volume is the smallest, so according to Boyle's law (i think), volume (V) is proportional (~) to the inverse of pressure (1/P), so as the piston moves up, decreasing the volume, the pressure increases, giving the compression ratio. The air is usually at about 1 atm entering the cylinder when the piston is at the bottom of its stroke (in an N/A engine, turbos create more hp by forcing more air into the engine, starting with a higher initial pressure). Then, as the piston moves up it compresses the air until it reaches TDC, when the volume is at a minimum and the pressure at a maximum. This maximum is usually about 10x more than atmospheric pressure (approx 10 atm), give or take a little. Thus you get the 10:1 ratio for compression. Or at least this is how I understand it, but I do know its not the mass that changes, its the volume and pressure.

Anyway... Whats the suggested octane for a non-turbo S4 FC? we have 89, 91 and 93 I think around here, i usually put the 91 in.

[AtroXR7]

MOST N/A vehicles run on 87 in america. and unless you change the timing, using higher octane just makes the mixture harder to burn, loosing efficiency. Im not sure how rotory engines work with octane levels tho, Ive never worked on one.

[SaintDrift]

My question is do other countries use the same octane rating as the US? I know Japan apparently has 102 octane, but if you ever look at the pump, they have some sort of forumla to come up with octane ratings. Is it the same internationally? I can't imagine our gas being so much shittier than everywhere else. We roll 93 octane on the East Coast.

[Emagdnim]

Originally posted by ToplessFC3Sman
a quick correction... The mass of the air/gas mixture does not change, because the number of particles doesnt change.

Your right I wasn't sure if it was volume or mass I was just to lazy to go search for there definition.

[AtroXR7]

Octane is available much higher in japan. But its also $5 a gallon or more. Its $5 + in Europe too. These are conversions of course, since they use the metric system everywhere else.

[SC_erritos]

how do you "change the timing?"

[AtroXR7]

depends on the car, some just arm yourself with a timing light and turn the distributor cap. High tech engines are harder, many have distributorless engines have fully electronic controls and you cant adjust timing without reprogramming the computer. I really dont know the import cars. Ive worked mostly with fords, getting to know nissans a bit better.

[marshun]

Originally posted by AtroXR7
depends on the car, some just arm yourself with a timing light and turn the distributor cap. High tech engines are harder, many have distributorless engines have fully electronic controls and you cant adjust timing without reprogramming the computer. I really dont know the import cars. Ive worked mostly with fords, getting to know nissans a bit better.

well its not the cap of the distributor. its the whole thing. i wouldnt recommend doing this if you dont know what youre doing. and when you adjust this then you shouldnt run lower octane levels. might ruin the head prematurely

[DoriAltis]

I'm in Cerritos, that 76 on the corner of Artesia and 183rd should have race fuel in 5 gallon drums, if not, they can always order some for you

[DoriAltis]

I'm in Cerritos, that 76 on the corner of Artesia and 183rd should have race fuel in 5 gallon drums, if not, they can always order some for you

[AE86GetSideways]

i live in Fresno California and the best fuel i can get is 91 off the pump for 2.42 a gallon.... its hard on the wallet, but i mix it with some 104 octane booster and when i want to go racing i can get some 105 fuel from my freinds sand rail shop but thats like 8$ a gallon. thats just what i do

[drftn13]

im not sure on the ignition timing of the cars you guys get there, but here in nz,
non turbo reccomended to run 96 octane $1.27 per litre
turbo reccomended 98 octane $1.36 per litre

our $$ is about half the value of the us $ and a gallon is about 3.5 litres??

[Feint]

I found a very rare case,94 octane right down from my house at the gas station I never use.It hovers around 94-98 cents a liter or 75-78 yen a liter,which is around $2.55 USD a gallon or something.I've never seen 94 anywhere else besides a select few chains of these stations.

[Ripper]

i live in cerritos too, but i refuel using mobile from marquart or exxon by that one taco bell, duno what's the intersection called. it's cheap in those places.

[AtroXR7]

Dont waste your $ on octane boosters from the store, they're absolutely worthless. Just a big marketing ploy.

http://tccoa.com/articles/misc/fboost.html

If you really need to spend an extra $5 on octane booster for every fillup to prevent detonation, then you're better off adjusting your timing.