octane preference

[rs_1101]

okay. i need some technical input here.. ive tried my car on 89 octane and 91, and i need to know from a scientific standpoint which would be better for the ep. the 89 is louder in my midpide (no resonator) and makes a definite resonant noise, the
91 is much quieter and no resonance noise, but im up in the air as to which one actually makes my car go alil bit faster.

im trying to compare this cuz i know our car runs rich on the ECU, but ive got intake/exhaust mods for more flow, and i know that that reacts differently with different octane ratings.

anyone care to comment?

[Lucid Moments]

The difference between 89 and 91 might be measurable on a dragstrip, or a dyno, but I doubt it myself. Go with the cheap stuff:cool:

[ADAMnQuickCIVIC]

I was a firm beleiver in premium gas until i actually tried 87 octane a couple tanks. I used to run Ultra 94 octane constantly. Running on regular my gas mileage increased from 22-24mpg on 94 octane to 29-32mpg on 87 octane. Performance did not decrease enough for me to notice, though I'll see the next trip to the track. I dunno if it's just me or not, but I do think my car is a bit louder on the 87 octane.

[DavidT]

91+ octane will make your car burn "dirtier" because it's a slower burning fuel to reduce preignition. Lower octane burns cleaner because it burns faster. If it burns to fast, there won't be enough fumes for the next stroke and the ignition strikes...preignition. Of course timing plays a big role in this as well.

I use 91+ (91 is all we get here in Ca.) because it basically reduces detonation...detonation leaves carbon deposits. Over time, large amounts of carbon deposits will build up if you run low octane gas and your car will always run shitty even with better octane and it's really hard to completely remove all the carbon buildup w/o removing the head off and sandblasting everything. My car has never seen anything below 91 so I can't attest to whether I get better mileage with a lower octane or if it's louder...maybe I'll try 87 on my next fill up ;)

Also, I believe 91+ octane is good for at least 3-5 additional HP because our ECUs are super smart. You'll probably get better ignition mapping, more aggressive VTC and all that because your car will detonate less. I think this is part of the reason why Hondata claims they get 7-10 HP with their remap is because they basically run a higher octane w/more agressive stock fuel/ignition remapping. It's not enough to fuel a big different, or enough for anyone to really care about, but it's probably a few ponies on the dyno.

[rs_1101]

well i know our ecu learns, but ive been reading on various aspects of the k20a3, for instance,
our car is meant to burn 80 octane.. thats why such low compression. the ecu is preprogrammed to run 87. now i ran some 89 for a week, and the ecu learned 89, now i filled up w 91, and it almost feels sluggish, im wondering if its just cuz of less noise comin out the a$$ end of my car.

hmm... dobbs.. where are you.. i know youve got something to say about this.

[Brettnyt]

87.... Just like a good hooker... Cheap and does a good job!

[civicSIracer]

Originally posted by Brettnyt
87.... Just like a good hooker... Cheap and does a good job!

you are one of the kids thats going to get some nasty STD.

[bobdobbs]

Originally posted by rs_1101
hmm... dobbs.. where are you.. i know youve got something to say about this.
I dunno. I'm not sure how our ECU would know if we're running higher octane, so I don't see how it would know to adjust for it. I believe we have a knock sensor and that would dial back the advance on the ignition timing if it detected knock (preignition). In that case, your ECU wouldn't have to "learn", it would adjust instantly, to keep your engine from being damaged. Maybe our ECUs will advance timing until it detects knock, so higher octane should give more power. Dunno. Gotta get me a Helm's manual.

I've noticed also that I get worse gas mileage with higher octane, but I can't explain it, so I doubt my observation.

[ADAMnQuickCIVIC]

Originally posted by bobdobbs

I've noticed also that I get worse gas mileage with higher octane, but I can't explain it, so I doubt my observation.

maybe your observation wasnt as clear cut as mine because i used to get 220 mi before my gas light came on (94 oct) now i get over 300 mi before it comes on (87 oct).

[bobdobbs]

Originally posted by ADAMnQuickCIVIC
maybe your observation wasnt as clear cut as mine because i used to get 220 mi before my gas light came on (94 oct) now i get over 300 mi before it comes on (87 oct).
This was a while ago, with a different car and I've never heard anybody else notice the same thing, so I figured I was mistaken. I'll try it again and see if I get similar results. Still can't figure out why it would happen, though.

[02SilverSiHB]

93 for me....better Throttle response and power band, imo

[Brettnyt]

Originally posted by civicSIracer
you are one of the kids thats going to get some nasty STD.

LMAO, hahaha... anyways, yeah, i just use 87 because my car seems to run fine on it, i havent tried anything higher... Too expensive for me to afford anything higher too... I would buy her a tank of it every once in a while, but ive heard that it is worse for the car to switch back and forth...

[rs_1101]

yes. well like i said i tried 89 and it seemed like the car had better pull with the 89 than the 91. and usually i know gas mileage can be an indicator of power. worse gas mileage usually means less power in some way, cuz ur cars gotta put up more gas to get u where u want with less power output

[Si3]

93 for me... anything less gives me rotten egg exhaust for the next 600 miles!

one tank of 87 gives me stinky exhaust for 2-3 weeks.

-Aj-

[bobdobbs]

Originally posted by rs_1101
yes. well like i said i tried 89 and it seemed like the car had better pull with the 89 than the 91. and usually i know gas mileage can be an indicator of power. worse gas mileage usually means less power in some way, cuz ur cars gotta put up more gas to get u where u want with less power output
Okay, how's this for a theory: The higher octane causes the gas to burn so slowly that our engine doesn't make full power with it. I.e., for a given amount of higher octane gasoline, our engines don't efficiently make use of the slower burn because the piston reaches the end of it's power stroke before the gas is finished burning. So a percentage of the energy of the gas is wasted. That would explain the worse gas mileage. If our engines were adjusting the advance on the ignition, we could take advantage of the slower burn. Since some have noticed no power benefit (and worse gas mileage), it would seem that higher octane hurts more than helps.

Anybody buying that?

[rs_1101]

thats the exact question im trying to raise here bob. excellent, and i know that alot of us believe in 91 octane (or 93 for non cali residents) but the fact that our motors are such low compression is making me wonder if there can be such a thing as too much octane.. we already dont have to worry about detonation because the ecu adjusts fuel maps according to exhaust readings.

i think im going to drop to 89 octane and give it a try. anyone else wanna take the octane change challenge? basically if your runing 87, next time ur empty fill up on 91 for a week, let it settle in then leave your comments, and for those of you on higher octane, give lower octane a chance.. id like to see if theres any clear cut preference.

i would also like to know how ignition mods affect this, im sure that with grounding wires or new sparkers maybe they could ignite higher octane more easily.. octane tuning.. lol

[esmith13]

Well, I'm locked into 93 as a minimum now, but I use Sunoco 94 daily, and 110 octane (purple) at the track.

Oh, and even when I was stock, it was SWEET AS HELL to drive around on the street with the left over 110 octane gas!!!

You HAVE to try that @ least once!!

Eric

[rs_1101]

yea but your cybernation FI style..

[ADAMnQuickCIVIC]

Originally posted by esmith13
Well, I'm locked into 93 as a minimum now, but I use Sunoco 94 daily, and 110 octane (purple) at the track.

Oh, and even when I was stock, it was SWEET AS HELL to drive around on the street with the left over 110 octane gas!!!

You HAVE to try that @ least once!!

Eric

Why on earth would you put 110 octane gas in a stock Civic???
Correct me if I'm wrong but I don't know of any 110 octane gas that is unleaded.
You're asking for problems (ie: burnt oxygen sensor).

[rs_1101]

i think hes talking about FI though.. i know alot of kids who tell me that octane booster is god, but i was pretty sure that octane tuning was a very important part of racing

[2k2ep]

I've seen on a dyno before if I remember right the change in 87 to 91 was worth 2-3 hp over the rpm band but it will in my experience lower mpg. FI or not they do sell 110 oinktane unleaded, a shop in my city sells 120+. For me I figure its only a few bucks a month extra for premium so I run it for a lil down the road insurance.

[esmith13]

here is a link to Sunoco Race fuel web site directly to the specs of their fuel. What I got was the GT Plus 109 Octane. As you can see on this link, the 105 and 109 gases are UNLEADED. Oh, and the GT 100 Gas (the 105 octane) IS street legal and safe for all vehicles.

If you look up info on gas octane and engine compression, you can do the math and find out that the 109 octane gas IS indeed safe for the EP... Which is by the way what XLR8B4U was smart enough to do before we last went to ATCO.

Oh, here's that gas link:
Sunoco Race Gasoline Specs (http://www.racegas.com/fuelspecs/default.asp)

Eric

P.S. - I haven't been to the track FI yet, I go this friday comming... I did all this when i was basic bolt-ons only.

[swampdonkey]

Octane is a measure of a fuels ability to resist detonation. The higher the octane of a fuel the less likely it is to detonate. (spontaneously combust) High octanes are clean burning because they allow more ignition advance (which burns fuel fully) and have additives designed to make them cleaner. The additives are designed to bond with products of combustion such as CO and NOx and nuetralize them. In fact a law was recently passed that allows fewer emmisions addtives so fuels will probably start becomeing a little dirtier with the new legislation. It should be noted that "perfect combustion" will only produce two emissions, CO2 and H20. There are many reasons combustion does not happen perfectly in cars, but I don't want to get to far from the subject matter.

I don't know if higher octane will make the EP perform better. Some cars are programmed to at least decrease ignition advance to limit power on low octanes, but only some are programmed to advance timing when octanes higher than those recommended are used. That was in Car and Driver a few months ago. They tested a Ford truck and it had the same output with all fuels, but the BMW had increasing outputs from 87, 89, 93. One truck made more power on the lower grade fuels probably because as someone mentioned earlier it was not either generating enough spark or enough ignition advance to get full combustion of the higher octane fuels.

Ok so I know none of this was useful.....the EP will run great on anything......I run midgrade. I don't think it matters a whole lot although I wouldn't be surprised if there were about 2hp between each octane rating.

[DavidT]

High octane gas DOES NOT make your car burn cleaner. 87 will always be cleaner than 91+. And yes, octane does make a difference on our cars. If you look and read carefully on the Hondata website, partcularly in the Si section, they said changing from 87 to 91 octane was worth 2-3 WHP across the rev band.

[SiR_d1]

For me, I only use Ultra 94!! The reason being that I hardly drive the car a lot anymore so It basically just sits in the garage. So the good thing about getting the good gas is that it wont go bad as quickly:)

[mini-driver]

our cars run and are designed for low octane....the only reason to buy higher than 87(other than cali) is to stop your car from "knocking". i doubt any of our cars have knocked yet.....give 'em ten years and maybe. "knock" is actually the end gasses in the cylinder breaking down and pushing into the incoming charge which makes a concussion wave and the sound. pre-ignition is when the gases actually ignite, why? because of hot spots in the cylinder.... the two are different , but one may cause the other......okay? now as for the fuel itself....87 octane is 87 percent iso-octane and 13 percent normal-heptane. iso-octane is a strong molecule in an"H" shape and normal-heptane is a slightly weaker molecule that is straight"-----" each molecule burns at basically the same temp and speed and ultimate energy level.......it's just that iso-octane resists breakdown and auto-ignition from compression heat. so a bone stock motor will react basically the same to all fuels...one does not have more power than the other essencially.

the difference in say cali, would be their use of different additives(instead of iso-octane) to produce less "knock." such as "oxygenates" hear me....these are bad, do some research on the fuel yu buy and you'll learn something! oxygenates are used hydrocarbons, they have already been chemically attached to oxygen molecules and they "don't" burn! their only reason for being there is to be an anti-knock agent. that's all well and good, but it's like this....if you are really thirsty and you fill your 40 oz. cup up with ice and then water, try and chug the water but you only drank 15 oz. of fluid, then dump the ice out and do it again and again until you are not thirsty! it's basically the same with oxygenats in fuel. they go in one end and out the other.....but the o2 censors pick up the extra o2 and compensate because it's reading a lean mixture therefore it sends more fuel and your gasmileage goes in the tank!

sorry that was long winded
g