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civic premium vs regular vs octane boost

3K views 18 replies 15 participants last post by  webby 
#1 ·
First let me introduce myself I'm a newbie from Austin, Texas


Looking at buying a 08/09 civic si or 09 ex and was worried about having to buy premium all the time since it is 1.00 more a gall. The main reason I'm buying a car and selling my truck is to get better mpg. I was willing sacrifice mpg of the si vs the ex because the fun factor of driving it. But since I found out it suppose to use premium the overall cost for a 5 yr period for fuel went way up. Close to 4000 more than the civic ex fuel cost...

I friend told me today his sister in law has a 07 or 08 civic si and all she uses is regular...

I realize it is probably bc of the needing higher octane but at a 1.00 more a gallon it seems cheaper to add octane boost at every filling..


Does any use just regular or regular plus octane boost or mix regular and premium???

Any help would be much appreciated...
Thanks
 
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#3 ·
This guy answer your question beautifully..

It doesn't matter what you do as far as running the engine hard, bottom line is if you fire a cylinder at the wrong time, in the wrong direction (WHICH WILL BE AN INEVITABILITY WITH 87 OCTANE) then you will destroy your motor. If the people on here can't pay for premium, then get rid of the car.

If not, all you will do is increase the value of mine by making less Si's out there that run WELL. If you want to put 87 in, you could use it for years without damage, or only once. The choice is yours. A few bucks to keep it running smooth, or an engine swap. Your money either way.

I personally want people to know that anyone who has an Si and knew what they were getting will NEVER run less than the highest octane they can find. It is what it was made for. Those of you who bought it and didn't plan on premium fuel or the additional maintenance for this special car won't be using it for it's potential and makes the rest of us angry. We'll laugh at you when we're passing you in our cars that run like champs while you're either hesitating or have had to buy a clunker after your car quit.

I don't mean to offend anyone, just reiterating what serious owners are trying to convince you all of (not you in particular Bossman. I wasn't singling you out, I promise).

For the sake of the fuel door, the owner's manual, and other Si enthusiasts, don't skimp on fuel. It's not worth it. $20 gets me 320 Mi. at 72MPH easily. I would only use 87 if it were an extreme emergency. No exceptions. No one here wants to see an Si out of commission. We're only trying to help, not bash. Do what the car tells you. :)
 
#11 ·
I feel you man we have all been throug this conversation before. Look you can ride a horse without a saddle but its gonna hurt and your going to slip off . samething with si you can drive with regular but in the longrun its going to destroy your engine and mpg did you know that if you put the correct premium youll get better mpg than regular 87? When a car requires premium and you put 87 it needs more gas therefore it runs out quicker.
 
#13 ·
The computer will actually retard the timing to run with the 87. Im not saying its better for the car, but the computer wont continue to run like it has 91+. I ran 87 on my RSX-S for a while just to prove a point and when you were in vtec you could tell all the power wasnt there but i actually got more miles out of the tank.
 
#12 ·
It's not $1.00 more per gallon. I live in texas also, and it's only .20-.25 higher per gallon. If you fill up will around 10 gallons each time (like I do), then it's only $2.00 - $2.50 more per fill up. And the si is worth it. Trust me, it may seem like a big deal at first, but for $2.00 per 300 miles extra, the si is way more fun to drive.

Also, I've read that on octane boost, if it says 5 or 10 points, thats really only .5 or 1.0 octane points. 1 point on an octane boost is equivalent to .1 points of octane that we think of. Adding 10 points of octance boost to 87, would only give you 88. You would need to add 40 points of octane boost to get from 87 to 91. This is way more expensive than just purchasing 93 octane for 2.00 extra per tank.
 
#14 ·
I too ran 87 in my 93 prelude Si. All the time. The girl who had it before me did too. So did her Aunt that owned it before her (bought it new). I traded the car with 234,000 miles on the motor.

Does this mean it's OK to do? No. It means I got lucky. It was probably not as big of a deal on the old prelude Si Non-vtec 2.3L engine. It seems like the K20xx is a smaller, more "high-strung" motor. On my RSX-S I ran nothing but premium and my Si has seen nothing lower than 92 Octane.
 
#15 · (Edited)
Hey guys

I didn't mean to poke a sore spot...Haha I guess I should have searched a bit more b4 I posted

I was obviously a bit confused, 2 days ago when I filled up with regluar in my truck, I noticed premium was .92 more than regular and .01 less than diesel....

I was SHOCKED since I just found out the si took premium and was concerned.
Now hopefully, it was a fluke and it is normally not like that, maybe I caught them in the middle of a price or something, I'm not sure

And then my friend's sister-n-law uses regular in her SI.. THEN, I was REALLY confused

I actually wrote a really loooong post with math calculations and comparisons from edmunds but it got erased..

So the summary is
Over a 4 yr period the increase of fuel cost is about 2700. The difference of 56 a month. No biggie..

My brother has a basically raced prepped S2000. So Im a little bit familar with the vtec. Which added to my confusion of using regular..

Thanks for all the info... Sorry if I poked a sore spot.
Hope yall understand my confusion and Y I posted the question..
 
#16 ·
Well welcome to the site. :thumb:

I think at one point we all had the same concerns. I did anyway.

Test drive the Si and decide if the cost of upkeeping it is in your budget and go from there.

It's a great car and so much fun to drive everyday. If you don't drive aggresively (unlike myself) you'll get great mpg. There are people on the 8th that have gotten 40+ mpg, of course that's doing 65 mph in 6th, no vtec, and driving like a turtle everywhere.

So in a nutshell mpg will be determined by the way YOU drive. :thumb:

Joey
 
#17 ·
joey-
I've driven the s2000 quite a bit and have test drove the 08si and it seemed like I had to shift much more than the 6sp s2000. It feels like the gear ratios are really close together making it tougher in stop/go traffic and city driving.

I don't mind driving like a grandma on the highway, I'm really not much in a hurry these days..

Overall the difference is minimal so the chose is clear.. SI

Thanks for the info....
 
#18 ·
Yea I agree, it's a close trans, 1st gear is so short, 2nd is usable at 5mph. lol

If you do drive in city traffic a lot I'd suggest getting an Ingalls ETD. It stops the engine movement in the engine bay so shifting at lower speeds in stop and go traffic is much more tolerable. It's a $150 at corsportusa.com Just a suggestion bc it made such a difference for me driving in traffic all the time.

Joey
 
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