Kup4036

si in and getting it saturday!!!! my question is: do u really think u need to use the mid grade (89 octane?) fuel for an 07 si?? I could see maybe every other tank full, but always and exclusively?

whatcha all think?

sonitex1

I use only 93 oct. The book and the sticker on gas cap door says to use premium only.

gasaholic

That is exactly what I was thinking however, the book says you can use 89 and that premium fuel is suggested but not a must. I found this odd being that I have been under the impression that higher compression cars need higher octane. It does mention in the book that if you use lower than 91 that you could here engine knock in lower rpms. Now I have not had a naturally aspirated car in some time so I am not at the top of my game on this info. I also have a 06 GSXR and it has 12.5:1 compression and it only referrances unleaded gasoline with octane rating of atleast 87. So with this being said I would love to hear a good explanation on this and why the bike can handle that sort of gas with that high of compression vs a car needing such higher octane. I am actually going to start researching this due to my own overwhelming curiousity, but if anyone already knows the answer to these questions please chime in.

Kup4036

hey gasoholic; sounds like u know your stuff. i didnt even understand half of it. anyway, am anxiously waiting to see what u found out. I would really hate to keep buying the expensive stuff if I couldve gotten by with 87 oct. all along.

gasaholic

I run 91 as well just becuase I am guilty of doing what I have always been told, however I am curious why the book says what it says. Not too mention why the bike says to use 87. Personally I think you can get away with using lower octane, but seriously, knock is not good no matter at what rpm .Motors are equipped with knock sensor, which in turn tells the stock computer to retard timing and pull fuel/ add fuel to compensate for alot of diffeent variables, like bad gas, But I would still run atleast 89.

I made a mistake when I was typing my first post ( I was tired) the bike is 12.5:1 compression.

gasaholic

Everything that I have checked has said that the new Si has 11:1 compression ratio.

gasaholic

Funny enough, I was watching the news this morning and they had the editor from Edmunds.com on there talking about this very issue with premium fuel. He basicly said that same thing that I had previously thought. The octane rating on naturally aspirated cars that are still being controlled by the factory computer will make adjustments to fuel, and ignition to compensate for the use of lower octane fuels and you do not have to run higher octane to operate these vehicles safely. The whole reason for this is because of how advanced the sensors and actual computers are that run and monitor our car and others. The only time that it really is an issue of needing to use premium fuel is when you are talking about a car that uses forced induction of some sort whether it be a supercharger, turbo charger or even nitrous. But even in those cases if it is a stock system that comes with the car the stock computer should still make the correct adjustments to keep the motor running safe, keeping in mind that you will lose power due to these very same corrections the computer will make.

In my opinion when you are talking about using an after market piggy back system or a StandALone, or just taking an NA car and throwing forced induction on it then the stock computer can no longer reliably make adjustments to keep the motor running safe. Therefore you should always run premium to be safe. And on something that is turbo charged from the factory he even suggests that even though the stock computer should keep it running safe, it is not worth the risk. Now that is of course for forced induction cars so any car that is naturally aspirated from the factory still running na and using the stock ECU should be safe no matter what the fuel is as long as it is unleaded gas 87 or higher.

He also talked about the difference of using gas from a station that sells gas for a big oil company,i.e. exxon, vs a company that would sell no name gas, that the differences in gas basicly are only the detergents used and should cause no problem with the vehicle what so ever. However, to watch out for shady looking gas stations. Now I know from knowing people that have owned gas stations that this means to look out for crappy looking gas statison as they could be adding fillers in a sense to the gas there for polluting the actual gas potentially causing major issues, or in the case of forced induction cars that need higher octane could be buying what they think is high octane and it is really not.

gasaholic

Ok. I ran a full tank of 89 octane from Citgo. Now up until this tank I have ran nothing but 93 octane and I was getting around 360 miles to a tank. With that being said after I have been riding around with 89 I only got about 265 miles to a full tank. So with that being said from the stand point of saving money I would say,"buy higher octane".
I think this can be explained by the engine compensating for lower octane.

Luey

With the lower octane, wouldn't the engine's knock/ignition sensor kick in and just retard ignition? That would let the engine run on even 87 octane, but would also explain the worse mileage.

Kup4036

u mean using a higher octane can get you 7-8 mpg more? wow!! havent filled it up yet (only 83 miles on the car), but I guess I'll go wtih 89-91, but no way 93. that's way too costly in the long run, and cant imagine the mpg getting that much more.

SpecialKPB

isnt it only like 10 cents more per gal. from 87 to 93 Octane?

I'm thinking if your ok with spending the money for an SI, and the fact that you bought a beautifully crafted car such as an SI; that you would WANT to put in 93 to get all you can from the engine and avoid any remote possiblilty of a issue with knocking and such. thats just me - I also see your opinion in that gas prices suck; so if you can why not try to save some $$$ at the pump.

-K