93 octane in a 2007 Honda Civic

[alphatarget1]

You should tune it on a dyno to run 93 octane gas. lawl.

 

[Eli]

There is so much fail in this thread it hurts.

 

[EightySix Four]

If it's worth the extra $0.40 / gal to make your car feel like it gained 10hp, then sure.

100 octane on a chipped 335i, on the other hand is :thumbsup:

:thumbsup: JB4 FTW.

 

[Capt Caveman]

There is so much fail in this thread it hurts.

All you had to do was see who the OP was to figure that one out without even opening it.

 

[Rifter]

Only if you have turbo'ed it or installed very high compression pistons/decked the block/head to raise compression to 11.5+

 

[Blain]

i dont even know where the manual is.

^_^ Let me get that for you... > Click Here <

 

[Doppel]

91 or 93 + can of autozone octane boost and K&N = stop light monster, do it your car will own.

 

[yottabit]

91 or 93 + can of autozone octane boost and K&N = stop light monster, do it your car will own.

True dat, here's a camaro with a K&N
http://www.youtube.com/watch?v=3gg3wxS1LeU

 

[Blain]

91 or 93 + can of autozone octane boost and K&N = stop light monster, do it your car will own.

True dat, here's a camaro with a K&N
http://www.youtube.com/watch?v=3gg3wxS1LeU

It looks like a K&N filter added about 300HP to that car.

I'm headed off to AutoZone right now! :awe:

 

[JCH13]

i dont even know where the manual is. been putting 87 for a year. only a 25 cent diff between 87 and 93. 87 makes it run like crap. no wait, maybe its the 1.8L engine that does that.

Wait, I thought you were the biggest Honda fanboi snob ever...

Why does it need premium? Just because the compression ratio is 11:1? With aluminum heads and block it is more likely than not that it will run perfectly fine on 87. Aluminum carries heat away from the combustion chamber so fast that old rules on compression ratios and octane requirements are not valid. You actually have to raise the compression on all aluminum engines just to get back the power loss from not using cast iron.

If you run a higher octane that required you can actually LOOSE power and mileage since the fuel is harder to burn and thus you may not get complete combustion. I have verified this on a dyno more than once to non believers.

Probably because there is more actual fuel and less crappy stuff so (I think) you actually need less fuel. It's not that 93 is 'harder to burn' it's that there is more useful fuel in it, so you wind up running a little rich if you just switch from 87 to 93. I notice changing fuel grades, 91 vs 93, in the fuel trims in my MS3, it will adjust its fuel trims because it does closed-loop fuel correction with a wide-band O2. I definitely get better mileage on 93 vs 91 because of this, verified over 2,000 miles of driving cross-country.

 

[SandEagle]

^_^ Let me get that for you... > Click Here <

if that's legit, then thanks. ill try 89 and see how it performs

 

[996GT2]

if that's legit, then thanks. ill try 89 and see how it performs

There's not really a point to using 89. Unless your car specifically requires premium (in which case you need 91/93), 87 is fine and 89 won't make it run any better.

 

[SuperSix]

megafuckingfacepalm

 

[yottabit]

Why does it need premium? Just because the compression ratio is 11:1? With aluminum heads and block it is more likely than not that it will run perfectly fine on 87. Aluminum carries heat away from the combustion chamber so fast that old rules on compression ratios and octane requirements are not valid. You actually have to raise the compression on all aluminum engines just to get back the power loss from not using cast iron.

If you run a higher octane that required you can actually LOOSE power and mileage since the fuel is harder to burn and thus you may not get complete combustion. I have verified this on a dyno more than once to non believers.

You're right that it doesn't automatically need premium because of it's compression ratio- there are far to many other variables (cam overlap, timing, combustion chamber geometry, etc). However this particular motor does. You'd have to pull a shitload of timing from the K20 to get it to run right on 87. (Which is what the Knock Sensor would inform the ECU to do if you ever put 87 in it)

Also I had never heard the claim about aluminum heads being able to run higher compression ratios before. In fact in doing research I could find no substantiated evidence of it although it seems to be common folklore among hot rodders. I did find some evidence that doesn't necessarily counter it, but seems to indicate there is no major difference in the detonation characteristics between aluminum and iron heads: http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/index.html

Normally to get a "guess" for the type of fuel required I look at the hp/L and the age of the motor. Newer motors are a lot harder for me to judge. But for instance it's pretty easy to figure out that if the 90s Ford 5.0L requires 87 octane and makes ~200 hp, it's likely that the ~300 hp 5.7L Corvette LT1 would require premium.

Similarly a 2.0L making over 200 hp today naturally aspirated will still likely require premium. However a 150-160 hp 2.0L probably wouldn't. Go back 10-15 years, and a 160 hp 2.0L probably would require premium. Pretty much any motor that is ever on the cutting edge of hp/L is going to be running premium

 

[LTC8K6]

There would be less "actual fuel" in 93 octane vs 87 octane, if we were going to use such terminology...

 

[Vette73]

Wait, I thought you were the biggest Honda fanboi snob ever...



Probably because there is more actual fuel and less crappy stuff so (I think) you actually need less fuel. It's not that 93 is 'harder to burn' it's that there is more useful fuel in it, so you wind up running a little rich if you just switch from 87 to 93. I notice changing fuel grades, 91 vs 93, in the fuel trims in my MS3, it will adjust its fuel trims because it does closed-loop fuel correction with a wide-band O2. I definitely get better mileage on 93 vs 91 because of this, verified over 2,000 miles of driving cross-country.

Stop posting.

 

[JCH13]

Stop posting.

Note how I prefaced everything with "I think" because I wasn't sure, it is just something I've noticed and have discussed in automotive engineering classes. If you know something I don't, please feel free to correct me. If you don't know any better, then kindly shut the hell up.

 

[Paratus]

Interesting question, but we're missing some pertinent info about the car.

Does it have a wing? How big?
How many "Type R" stickers are the on the car?
What color did you paint the brake calipers and drums?

I don't see how we can answer the question until this crucial information is revealed.

 

[ShawnD1]

I thought SI's wanted premium?

Nah, the people who make the honda website are just stupid buggers.
http://automobiles.honda.com/civic-si-sedan/specifications.aspx
Required Fuel Premium Unleaded


The engine doesn't really need better fuel unless the engine knocks when using low quality fuel. The engine in a Civic Si is really damn expensive to replace so it's probably best to just follow the manual and use premium anyway. The computer probably keeps track of knocking as well so they can void your warranty when they find out you've been using bad fuel and it's been knocking for months and that's why it's so broken.

 

[ShawnD1]

Probably because there is more actual fuel and less crappy stuff so (I think) you actually need less fuel. It's not that 93 is 'harder to burn' it's that there is more useful fuel in it

Usually it's the other way around. Molecules with higher octane ratings tend to be lower energy density. Ethanol and propane are very low energy density, very high octane rating. Diesel is very high energy density but very low octane rating. Cyclohexane and benzene are a good comparison; while both are very similar molecules, the benzene is more stable, benzene releases less energy when it burns, and benzene has a higher octane rating.

It makes a lot of sense if you think about what the octane rating means. Things with a high octane rating are harder to burn. You can compress and heat the hell out of ethanol and it will not explode until there is a spark. That molecule doesn't want to burn, it's already in a low energy state, and it doesn't release a lot of energy when it does burn. Fuels with low octane ratings are the exact opposite. If you compress diesel, it explodes. If you heat diesel, it explodes. Even when there's no spark, it explodes. Heavy fuels like diesel are very high energy, they are unstable, they release large amounts of energy when they burn.

This doesn't just apply to things like gasoline or ethanol. It applies to explosives as well. If an oxidizer like sodium perchlorate is ridiculously unstable, then you can be sure that it releases a huge amount of energy when it reacts with something.

 

[Throckmorton]

Diesel has a very high octane rating, not low. But yeah it has nothing to do with energy content

 

[Doppel]

I've heard the octane on rocket fuel is so high it won't even light with a match. That may be bullsh*t, though

Yeah, probably is!

 

[Blain]

I've heard the octane on rocket fuel is so high it won't even light with a match. That may be bullsh*t, though

Yeah, probably is!

Why post that rather than simple doing a Google search?

 

[ShawnD1]

Diesel has a very high octane rating, not low. But yeah it has nothing to do with energy content

If you put a little bit of diesel in your gasoline, the gas engine will knock like a bitch. It dramatically lowers the octane rating of the fuel.
wiki says diesel is around 15-20 octane rating
http://en.wikipedia.org/wiki/Octane_rating

That terrible knock is actually how a diesel engine works. Diesel engines do not have spark plugs.

 

[yhelothar]

Wow. An econo-box engine that needs premium? Another fail point for the Si...

The Si specs look pretty good, if the car was from the 80's.

LOL @ calling a 100hp/L high-revving, high compression, naturally aspirated engine an econobox engine just because it's from a civic.