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I am thinking of buying a 2006 Civic Si. My only concern is that I have read Honda's brochure and it recommends using high performance fuel ie. 91 octane. My question, can the Si run off 87? I know I won't get the top performance, I am just looking to improve gas efficiency.

Thanks in advance,
Brian

 
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dont do it... whatever the manual suggests, thats always best for the engine. Like if u want ur Si to last u a good while without knocking and crap like that, i highly recommended 91

If price for fuel is a concern, y even by the car, that shoulda been calculated when getting ready to buy a new car.

 
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He speaks the truth, if you run the lower octane it will "Diesel" and you don't want that. I also suggest purchasing your fuel at a reputable station. Do not buy bargain gas. You will get what you pay for.

Just do a search for gas or something and read up.

 
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id recomend useing the 91 also

 
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does the manual say anything else about using lower octane fuel?

 
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i run 93 for no apparent reason. 87 and 91 octane fuel isnt that much more a differnce in price. ecspecially in a honda. bargain gas?? wat the hell is that. will that really make a HUGE difference in the long run..

 
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if you are planning to use 87 for fuel efficency reason, then you are in for a big shock...

you are going to get WORST gas mileages than if u were useing 91octace.

the car was designed to use and maximize(the efficency) of 91 octane

 
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11:1 compression will HATE 87 octane. It will pull timing out until it runs out of timing to pull, then throw a CEL cuz the motor will knock under heavy load.
Its an extra $2.50 in a tank. If you cant afford that, then pick another car.
There's almost no high performance motors these days that run on regular.

 
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That is the gas you get when you fill up at the no name gas stations, for example Loves, Murphy USA, Diamond Shamrock, and all the other stations that do not advertise a particular brand of gas. These stations buy their gas from the cheapest seller, they care not how old or the water content of the gas. Yes, there are federal standards that they must follow. Most of these stations will barely meet the minimum standards. To answer your other question. Yes, it will make a Huge difference. In the log run buying 2nd grade gas will cause fuel system problems and accelerated where on the internals of the car.

 
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don't listen to the manual, put 87 in...

 
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My mom has an 02 Altima with the 3.5 V6 and we've put 91 in it every time except the rare occassion of the station not carring it(out in the country and really needed gas). After over 60k the motor is still running perfect so I HIGHLY recommend using what the manual says, since thats what they designed/tuned the motor to run off of.

If it could run off the cheap stuff properly they wouldn't tell you to use 91.

EDIT: On the "bargain gas" DON'T get it. I filled up at a place down at school and my car ran like ****, my stock lil 1.7 didn't like the cheap gas, plus I got horrible gas milage. I didn't think it mattered that much until I actually used it.

 
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the higher the octane, the longer the fuel lasts it seems to me. so i use 93...i think its liek a 20 cent difference where i live from 87 to 93...so why not.

 
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Hey its okay to put 87 in it! LOL HA HA HA Just hope you dont plan on having that car for long. I mean seriously your willing to spend the 24000 on the good car then not the money on gas.. I mean what is that?

 
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your a dumbass

 
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dang not so harsh man just mis-informed

 
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well if thats what the manual says than do it, doesnt take a rocket scientist to figure that out

 
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yea truth

 
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use shells.

 
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you shouldn't run 87 in a k, period. granted you CAN, but only in an emergency situation. i'm pretty sure that if you put that low of an octane in it, the ECU recognizes it and runs in limp mode. I just run 93 in my K, and 94 when it's at any station.

 
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Heres and idea.. Save your money. Buy a k-pro,upgrade your fuel pump, add fuel pressure regulator, some 1000cc injectors, and have a tune for 85. Then you can save as much money as you want and basically be driving around on race gas all day

and then get a 2nd tune for 87 that wont let you rev above 3000.

 
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why wouldnt you want to follow the manual?

 
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Ill give you a hint:

 
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def on a k spend the money for 91 or 93, which ever is available for you. Always use a good station also, around me its Marathon or Shell for good gas. Please avoid using Giant Eagle (GetGo) or other gorcery store gases. I saw an evo filling up at one the other night as I drove by and it almost made me sick.

As a double check , The d series engines in our cars run fine on 87 right because of the engine temp? so there is no need to run 89 or 93.

 
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yeah our d17 is lower compression, 87 is perfect for it and using higher will do more harm since it doesnt get hot enough to combust all the fuel. using 87 will give most power and higher mileage.

 
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yea a locked thread with what mods

 
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My S197 Mustang GT uses 87 octane gas and makes 300 hp on over 10:1 compression. I too was wondering about using 87 in the Civic Si. Has anyone tried it?

How does the factory plan to void your warranty if something bad did happen? There's no way to make sure you get the highest quality 91-93 octane gas all the time.

 
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why use it if you really aren't saving that much more money over using what they suggest? And you don't want to get in a pissing match with Honda about a warranty either. Especially since it tells you what to use there is no real reason to do otherwise.