what octane fuel?

[Ludi Mali]

I thinking about the possibilities for my engine and when considereing the high cr n/a route, i was wondering is there a way to figure out what octane fuel you'd need to run for a specific CR. like if i went with an 11:1 or 12:1 (hypothetically) how would i be able to know what octane fuel to use?

[A20A1]

I've seen things like this:

9.1:1 = 91 octane

10.1:1 = 101 octane

However with the proper fuel/ignition engine management you can bump that down... cause I've heard of people running 11:1 C/R and still use 92-94 octane. Of course they run a higher octane at tracks but daily driven is what I'm referring to.

Make sure you get the right heat range for spark plug.

The egr in most moder cars I assume helps manufacturers increase the CR and still run off of pump gas.

I liked 89 octane when I had the A1, now that I'm running an A3 block the car runs better with 92, of course this is the A3 block without the EGR, since I'm still carbed and have no ECU running things, so you can see why it's nessescary to go with the higher octane.

[AccordEpicenter]

11:1 you could possibly get by on 91 oct but you shoud retard your timing a little bit, 12:1 im not sure about, it might be ping city even on 93

[shepherd79]

the higher the compression, the higher the octane should be.
you can run 92-94 octane fuel on B16 motors all day long and they will be fine and they have 10.4:1 compression.
if you are going with 12:1 you may start want to mix your own fuel, 50% 92-94 octane and 50% something higher like race fuel.

[POS carb]

the Accords have a shittly rod-stroke ratio, I wouldn't recommend anything higher than 10.0:1
I have not tested this though.

[SteveDX89]

My engine is 10.2:1 and the minimum octane I can run is 91. ITR's run 11:1 compression and still use pump gas.

[treadhead 1952]

I agree with Eric's reply, anything designed to run hi revs to make power has a hard time with hi compression with regular pump gas. It wasn't too bad when you could go fill up at the airport with Phillips Avgas, the blue stuff at about 104 octane. I have wondered about supercharging one of these little beasties, you can lower the compression ratio that way and still make big RPM/Power numbers, course',you run the risk of blowing the head off ;-)

Jay treadhead 1952
Las Vegas, NV

[Ludi Mali]

yeah i was kinda trying to get a general idea how high i could possibly go for a daily driver.

[treadhead 1952]

Mine, '88 LXi Hatchback MT, runs well on 91, give it 89 and it tries to make rude noises at odd moments. That tells me anything more than factory box stock and you're out back mixing methanol and Phillips Flight fuel so it don't make those self same rude noises or worse. The more alteration off the original and you wind up changing what they figured was the best of what the combination could do.

My experience is with the Bow Tie brigade and four bolt mains and forged cranks to with stand the 13.5 to 1 of a heavy breathing Rat block(427). I had more success by lowering to 8 to 1 and sticking a GM 6-71 Supercharger on a Weiand manifold. That and a Holley Strip Dominator in 1350 CFM flavor made a '66 Chevelle go into the 11's and 10's. That was a while ago and the car was producing in excess of 700 ponies. Even then I never ran anything less than 92 octane, 98 if I could get it.

[NXRacer]

if you understand what the purpose behind octane ratings is for then you''ll know that anytime you up the compression (either n/a or by boost) then you need to up the octane rating also. Octane changes the flashpoint of the gasoline. If you have higher compression you need a higher octane so you dont get pre-detonation which is a BAD thing.

if you're running high boost or high compression you'll need to run race gas. Most times you can get away with pump gas if you have good spark/fuel management to keep the pinging/detonation away.

[Ludi Mali]

I understand the what the ratings mean, just not sure on how much you have to increase the octane rating for going up a certain amount in cr. howstuffworks.com has good info on how octane ratings work, for anyone that doesn't know.

[FoX]

I use the highest octane i can get mainly because it burns better and the shop manual says to use 91 octane or better.

[SteveDX89]

I use the highest octane i can get mainly because it burns better and the shop manual says to use 91 octane or better.

What manual says that? Read the back of your owners manual. It tells you what to use. Anything more is a waste of money.

[shepherd79]

the shop manual says to use 87 octane. i use 87 octane, and my car runs just fine. no pinning, no valve rattle.
plus on the top of that i found that my car runs better if i use 87 octane instead of 89 or 93.
if you have stock car, like i do, i would only recomend using 87 octane. anything higher and you are giving away your money to oil companies.

[AccordEpicenter]

i have to use 93 now that im boosted... but my LXI ALWAYS ran better on 89 vs 87... but not much better from 89-91 or 93

[Ludi Mali]

i think you guys are missing the aim of this thread.

[smufguy]

i think you guys are missing the aim of this thread.

well they already lost it. BUt im sure you got your question Answered in this crazy maze. higher the compression, the higher the octane rating so its 91 or 93 octane depending on what state u live in. For a stock compression of 9.5 or below people use 87 octane and between 9.6 to 10 they tend to use premium fuel. It all depends on manufactures preference and what it says on the sticker. I mean the Infinity J30 (210hp) that my aunt has runs on premium fuel and she got 10.56 cr and the new accord V6 (240) runs on 87 octane and it has 10 cr. so its basically engine dynamics and what not.

So for you, using 11 cr for this block, you are gonna use highest octane provided at ur state/any state.

[Jareds 89 LX-i]

There's really no cut and clear answer to this question, becuase it all depends on the individual engine and how it's designed/built. Unless you're really high compression (in which you just use premuim), just try a few different grades until you find one that works with no pinging or otherwise strange side effects. I know with my 3g (with a slightly shaved head which = higher CR) always did better on 89 vs 87. Anything higher than that made no difference.

My bike has a 12:1 compression ratio and it does fine on 93 octane

[Blkblurr]

My S2000 has an 11.1 to 1 compression ratio and I run 93 octane and have no pinging. Honda recommends 92 Octane minimum for my engine.

[smufguy]

My S2000 has an 11.1 to 1 compression ratio and I run 93 octane and have no pinging. Honda recommends 92 Octane minimum for my engine.

wonder how they drive around in Cali with 91 octane. but again, they get special engine mod for that stupid state.

[A20A1]

What I was saying eariler is it depends on the engine management... I'm sure the newer Accords and S2000 all have ECU's that can handle the different grades in gas... not saying it knows what gas you put in... but the effect of a lower or higher grade is picked up by the ECU and then it just runs with different fuel, timing, and EGR outputs. As a result you'll get less power with a lower grade of gas and a higher CR... but in our Accord I doubt our ECU has any way of changind based on the effects of a certain grade of gas... IMO

[Ludi Mali]

that makes sense

[smufguy]

What I was saying eariler is it depends on the engine management... I'm sure the newer Accords and S2000 all have ECU's that can handle the different grades in gas... not saying it knows what gas you put in... but the effect of a lower or higher grade is picked up by the ECU and then it just runs with different fuel, timing, and EGR outputs. As a result you'll get less power with a lower grade of gas and a higher CR... but in our Accord I doubt our ECU has any way of changind based on the effects of a certain grade of gas... IMO

the chemical composition of the gasoline is the same for all octanes, its just the different level of iso-octane and other stuff that changes and they dont contribute to the combustion by product. as in u dont get higher CO burning 87 as opposed to 93. If any, the ecu has to go with the knock sensor. Just like the mitsus do on their turbo motors. U can run 87 on their motor and run fine without a problem, but they prefer 91. the only reason you make more power in higher octanes, like race gas and stuff is cause of the ECM which controlls the ignition and stuff can actually advance the ignition to get more power. And thats what the standalones and piggybacks are good for. Controlling the combustion process.

and yeah, the winter gas is different from the summer gas. ;)

[Ludi Mali]

bleh, i fear the coming of the winter gas

[AccordEpicenter]

smurf... youre not gonna see 240hp with the honda v6 unless youre on premium fuel... on 87 the knock sensors will pull out alot of timing

[A20A1]

the chemical composition of the gasoline is the same for all octanes, its just the different level of iso-octane and other stuff that changes and they dont contribute to the combustion by product. as in u dont get higher CO burning 87 as opposed to 93. If any, the ecu has to go with the knock sensor. Just like the mitsus do on their turbo motors. U can run 87 on their motor and run fine without a problem, but they prefer 91. the only reason you make more power in higher octanes, like race gas and stuff is cause of the ECM which controlls the ignition and stuff can actually advance the ignition to get more power. And thats what the standalones and piggybacks are good for. Controlling the combustion process.

and yeah, the winter gas is different from the summer gas. ;)


Where did I say gas had a different chemical composition... I'm not talking about emissions or combustion byproducts... my reference to EGR was that it helps reduce cylinder temps to prevent knock without needing to retard the ignition to any great degree.

[smufguy]

Where did I say gas had a different chemical composition... I'm not talking about emissions or combustion byproducts... my reference to EGR was that it helps reduce cylinder temps to prevent knock without needing to retard the ignition to any great degree.

no i was just mentioning it :D i know what u were talking about mike, i was just adding in ;)

[smufguy]

smurf... youre not gonna see 240hp with the honda v6 unless youre on premium fuel... on 87 the knock sensors will pull out alot of timing

jason, thats what the 7th gen V6 runs on, 87 octance and their manufacturing spec was 87 octane. Look at the honda.com website. U will see under the V6 engine, it uses regular unleaded.