hey read!!, well... Options

[6strngs]

The air fuel ratio takes time to burn. if you light the spark plug at 10 degrees BTDC then by the time the mixture has finished burning you are probably around 20-ish degrees ATDC, this is your peak pressure and it actually pushes the piston on it's way down to help spin the crank which helps lift the other pistons up on their strokes and it just happens over and over. now, if you light that spark a little earlier and you can make peak pressure a few degrees earlier it helps push the piston down faster thus creating more power. You run into problems when you advance too far so that you reach peak pressure at 0 degrees or even BTDC so while the piston is still on it's way up, the explosion pushes it down and the piston has to fight against that extreme force. this is detonation and will kill an engine pretty quick.

But, a gasoline's octane number tells us it's ability to resist detonation so the higher the octane, the less chance of detonation which is why it's safer to use a higher octane when advancing the timing.

[FortuneCookie]

Ok dudes... After 3 months of driving with advanced timing to 16 degrees, I would have to say I LOVE THE RESPONCE AND GAIN! BUT!!! I have to go back to 10 degrees stock becuz I drive 60+ miles everyday to and from work. And that is causing me to pump $35 of 93 octane gas every THREE days! Looked at my budget, kinda hurts me on the long run. This is a GREAT way for gains for stock. But not a great if you drive it too much.

[GriffGirl]

Something is seriously wrong with your car if you're only getting 180 miles on an ST. I drive 40 miles a day and average 365 miles to a tank in cold weather w/stop & go traffic. Unless of course you're driving 60 miles EACH way in which case OOPS.

[808celica]

WTF!!!!!!! i checked my timing with the gun and mines is set @ 15 i think..............DAMN!!!!!!!! the whole time i didnt know...........CRAP is that bad??? i always use 89 octane cuz gas here in hawaii blows how do i adjust if a little closer to 10??? i dont know if i have knock..........but my cars seems to idle a little rough but it doesnt drop past 800rpms..............it just feels rough...........damn maybe i have a slight knock..........CRAP!!!!!!

This post has been edited by 808celica: Jan 9, 2008 - 5:39 PM

[FortuneCookie]

Lol. Well GriffGirl, 60+ miles everyday, 95% of it highway miles. And btw 808Celica, you can use 89 octane gas for 15 degrees. People have done it and have nothing wrong with their motor. But if you turn it a tad higher, I would seriously recommend 91 or 93 octane.

http://www.toyotacelicaonline.com/timing.htm

[6strngs]

what's the price difference between 87 and 93? like 0.25? so you're spending aproximately $3 more by filling up with premium? people are willing to drop like $200 on an intake and $500 on an exhaust, this costs you ~$7 a week and gives similar gains to those mods. seems like a good deal to me. but w/e

[FortuneCookie]

Well I'm not one of those people who are welling to spend $200 on an intake that does the same thing as a cheap ebay one for $30. But you are missing the point here 6Strngs. The higher the octane, the better the fuel burn and less chance of detonation. That means alot more gas consumption, and that means the more you pay for gasoline in a shorter amount of time that you would pay for a 87 octane. PLUS the timing advancement, which would equal to more money spent on gasoline overall. Then you add alot of highway miles which equals even more money spent on gasoline. Get my drift? Lol.

[6strngs]

Well I'm not one of those people who are welling to spend $200 on an intake that does the same thing as a cheap ebay one for $30. But you are missing the point here 6Strngs. The higher the octane, the better the fuel burn and less chance of detonation. That means alot more gas consumption, and that means the more you pay for gasoline in a shorter amount of time that you would pay for a 87 octane. PLUS the timing advancement, which would equal to more money spent on gasoline overall. Then you add alot of highway miles which equals even more money spent on gasoline. Get my drift? Lol.

actually, the higher the octane, the slower it burns. I'm sure you could get away with 89 octane for 16 degrees BTDC. but if you really think you get better gas milage with retarded timing and lower octane, then go for it. the only way you get better milage is because the car is slower so you won't be as inclined to put your foot into the gas pedal.

[Bitter]

i've been watching knock numbers on my safc2 with 15deg and 89 octane. i had my injectors cleaned at work on the machine and my knock counts dropped alot, im seeing the max counts at or under 100 now during WOT pulls in 2nd gear to 6500 rpm. the pcm is pretty fast to pull timing which i can see on the safc because knock only flits up for a split second and then is gone. thats the PCM detecting knock and then immediately pulling some timing to control it. i dont feel like messing with the timing anymore, 15 deg is enough for me and 89 octane isnt such a big price jump from 87.

[FortuneCookie]

actually, the higher the octane, the slower it burns.

Are you sure? How come everytime I put 93 octane in my gasoline tank, I tend to burn more gas? Especially with my Prelude which eats up gas like a mother with 93 octane! Even my buddy told me the higher the octane, the more it will burn. Someone needs to try it with STOCK settings. See how many miles they would get from 87 octane, and then see how many miles with 93 octane. Just test like 1 or 5 gallons.

This post has been edited by FortuneCookie: Jan 11, 2008 - 12:24 AM

[6strngs]

I'm taking college classes with a major in automotive technology. One class I took last semester was titled "Fuel induction and emissions" in which we talked about gasoline and all the gasses that come out the tail pipe and what they are and how they get there. We covered timing, and the properties of gasoline in that class. I'm sure that higher octanes burn slower. But, what I mean by burns slower does not mean better gas milage. it burns slower in the combustion chamber giving it a better resistance to knock.

Peak pressure, or the point where the pressure in the combustion chamber becomes the greatest to where it forces the piston down, thus spinning the crank, thus moving the other pistons and keeping the car running, should be around 10-20 degrees After top dead center (ATDC). Now, gasoline takes a few milliseconds to burn (approx 2-3 mS) so you fire the spark plug before the piston reaches top dead center (BTDC) so that a few mS later when the piston is on it's way down, the explosion actually occurs. Imagine pedalling a bicycle, when the pedal comes up and around you wait until it's a little bit past the top and then push down on it with your foot and it gives you propulsion. now, if you were to step on the pedal when it was already halfway through it's trip down, you wouldn't get as much power as if you stepped on it right as it passed the top mark. That's how advancing the timing gives you power. However, fire the spark plug too soon and the explosion will happen too soon happen while the piston is still on it's way up and make it hard for the piston to complete it's revolution. That's knock. at idle, we could get away with advanced timing, but as you drive, your timing is always changing, and sometimes under high load, such as wide open throttle, it'll be so advanced it'll begin to knock, which is why we use higher octane gas. This way the gasoline takes longer to burn and preventing knock by delaying the peak pressure slightly.

That said, I don't really see how a higher octane gas could give you worse gas milage. except maybe because it burns slower, it doesn't give as complete of a burn because it's doesn't have enough time to finish, and so more of it just gets wasted out the tailpipe, but that's the only thing I can think of.

[FortuneCookie]

Regardless of all the classes you take and notes you want. I'm still getting lower mileage out of higher octane. Maybe like GriffGirl said, something is wrong with my car. It isn't the average ST. It is quite quicker.

This post has been edited by FortuneCookie: Jan 11, 2008 - 3:05 AM

[Bitter]

if you're timing is retarded or is being retarded then higher octane will give lower fuel economy. double check what its set at, if the ecu is pulling timing all the time because its hearing knock (even with 93 you can knock) then fuel economy will be affected. the ecu works soo fast you never feel it or hear it unless its soo severe its causing damage. try getting your injectors cleaned by a shop with a machine and have the top end de-carboned.

[808celica]

Lol. Well GriffGirl, 60+ miles everyday, 95% of it highway miles. And btw 808Celica, you can use 89 octane gas for 15 degrees. People have done it and have nothing wrong with their motor. But if you turn it a tad higher, I would seriously recommend 91 or 93 octane.

http://www.toyotacelicaonline.com/timing.htm

now way imma leave it at 15` imma bring that shiz down to 10 or something...........maybe there's something wrong with my car?? could that be it??? he turned up the timing to hide a problem with the engine??

[6strngs]

Lol. Well GriffGirl, 60+ miles everyday, 95% of it highway miles. And btw 808Celica, you can use 89 octane gas for 15 degrees. People have done it and have nothing wrong with their motor. But if you turn it a tad higher, I would seriously recommend 91 or 93 octane.

http://www.toyotacelicaonline.com/timing.htm

now way imma leave it at 15` imma bring that shiz down to 10 or something...........maybe there's something wrong with my car?? could that be it??? he turned up the timing to hide a problem with the engine??

make sure you check your timing with the TE1 and E1 terminals in the diagnostic box jumped. my friend forgot to do that on his AE86 corolla and tried to advance it a little, then was having problems with a lack of power a little bit later, checked his timing and reset it to stock, but still had the same problem. then later found out he needed to do that, went back after jumping them, and saw his timing was retarded 15 degrees below spec!

[n1ckz0r]

I loled at this thread becuase of the confusion and how many people asked like the same question over and over just different ways.

[Rayme]

octane rating is a rating for the self-ignition properties of the gas..not how fast it burns...?
Maybe you should have mentionned that too.

I'm taking college classes with a major in automotive technology. One class I took last semester was titled "Fuel induction and emissions" in which we talked about gasoline and all the gasses that come out the tail pipe and what they are and how they get there. We covered timing, and the properties of gasoline in that class. I'm sure that higher octanes burn slower. But, what I mean by burns slower does not mean better gas milage. it burns slower in the combustion chamber giving it a better resistance to knock.

Peak pressure, or the point where the pressure in the combustion chamber becomes the greatest to where it forces the piston down, thus spinning the crank, thus moving the other pistons and keeping the car running, should be around 10-20 degrees After top dead center (ATDC). Now, gasoline takes a few milliseconds to burn (approx 2-3 mS) so you fire the spark plug before the piston reaches top dead center (BTDC) so that a few mS later when the piston is on it's way down, the explosion actually occurs. Imagine pedalling a bicycle, when the pedal comes up and around you wait until it's a little bit past the top and then push down on it with your foot and it gives you propulsion. now, if you were to step on the pedal when it was already halfway through it's trip down, you wouldn't get as much power as if you stepped on it right as it passed the top mark. That's how advancing the timing gives you power. However, fire the spark plug too soon and the explosion will happen too soon happen while the piston is still on it's way up and make it hard for the piston to complete it's revolution. That's knock. at idle, we could get away with advanced timing, but as you drive, your timing is always changing, and sometimes under high load, such as wide open throttle, it'll be so advanced it'll begin to knock, which is why we use higher octane gas. This way the gasoline takes longer to burn and preventing knock by delaying the peak pressure slightly.

That said, I don't really see how a higher octane gas could give you worse gas milage. except maybe because it burns slower, it doesn't give as complete of a burn because it's doesn't have enough time to finish, and so more of it just gets wasted out the tailpipe, but that's the only thing I can think of.

This post has been edited by Rayme: Jan 20, 2008 - 10:37 AM