I recently purchased a used 2008 Civic Si Sedan - I'm really enjoying the car! I think the salesman misled me a bit when he said that a relative's Civic (I'm guessing not an Si) got 40mpg on the highway. In any case, is there a setting on either the dash or the navi that actually shows avg. mpg at any given time? If there is, I haven't found it yet.

 

There isn't one. You have to calculate it yourself.

 

OK - thanks. That's a bummer. I guess honda concluded that people driving Si's wouldn't care about gas mileage. Is it your understanding that Si's MUST take premium gas?

 

Premium gas is recommended you can run crap gas if you choose but the computer will pull timing and remember that it burns less evenly in the combustion chambers, for larger bore motors like the K20 that can take a toll on internal components over time.

 

Our engine uses premium gas because of the compression rate. Higher octane fuel is actually harder to burn that lower octane. If you run low octane fuel in our engine you run the risk of predetonation, meaning the fuel combust from the compression and this is a bad thing.

To the mileage question, I got just under 38 miles to the gallon in my Si on a trip from El Paso, Texas to NW Arkansas. Average speed was 60mph and I had to hypermill like crazy but I got it. I normally get a combined of around 28 IIRC (this is when I'm having a lil vtec fun also). I've gone in the low 30s combined taking it really, really easy.

 

I'm averaging 22mpg city with lots of vtec.

 

Yes it MUST take premium.

 

i think the r18 civics do get 40 mpg on the freeway, definitely not the si though . i get around 27-30 mpg mixed city/highway depending on how i drive.

 

thats why i like the new si's so much. the older ones are great too.