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cistercian 06-06-2016 11:21 PM

Civic Si better than hoped!
I joined this forum originally with a 1995 civic ex.I could squeeze 50+ out of that car...but at 320k it began to become inefficient.My father gave me a 2003 Si which due to poor CD, gearing and low compression never did do very well...but it was free so I drove it until this past thursday when a full size chevy hit me while I was stopped for a light...he was going 45...the 03 Si was annihilated...and I am apparently ok.I hope.

Anyhow I needed a new car so I bought a 2013 honda civic Si Coupe.It is rated 22 city 31 highway and 25 combined.I figured those numbers to be very low and had good reason to believe I could do better...for the following reasons: The new car has a better CD than the old one.The bottom is almost completely almost has a full belly pan stock!The engine, while larger at 2.4 vs 2 liters had a 11 to 1 compression ratio vs 9 to 1 for the old car.The new engine gained it's displacement by being stroked...which is good for torque and low rpm operation...and the car has a 6 speed close ratio transmission with decent low rpm at cruise vs the old cars very high highway rpm.I went 100 miles and then back on the same route and got 42.3MPG.The best leg of the trip was 45.6mpg...much better than the paltry 31 the car is rated at.I enjoyed a WOT excursion which cost 1.5mpg at least!This car has exceeded my expectations.My next goal is 48.Heavy traffic prevented really good technique...

I am very pleased.The car is a real rocket but properly handled capable of pretty decent fuel economy.I use shell premium only.

Not bad for a hot rod!

California98Civic 06-06-2016 11:48 PM


Originally Posted by cistercian (Post 515824)
... I went 100 miles and then back on the same route and got 42.3MPG.The best leg of the trip was 45.6mpg... ... Not bad for a hot rod!

Not bad at all. This is a manual transmission, yes. No turbo on the Si I believe. What techniques were you using?

MobilOne 06-07-2016 12:59 AM

And out of curiosity, why the Shell premium?

elhigh 06-07-2016 08:55 AM


Originally Posted by MobilOne (Post 515829)
And out of curiosity, why the Shell premium?

11:1 compression ratio. Reason enough, or at least it used to be.

I imagine the computer would retard the timing if you used regular, though.

cistercian 06-07-2016 11:06 PM

I found even my old 9 to 1 Si got much better mileage with shell premium.Going up mountains with a good load would pull back the timing on regular...which really hurt mileage.
The 2013 Si is a normally aspirated 2.4 liter DOHC engine with a 87mm bore and 99mm stroke.It requires a minimum of 91 octane.It is port fuel injected.The new direct injection versions of this engine in the Acura TLX are 11.6 to 1.
Technique used is allowing speed to drop off slowly approaching summits, but not more than 5 mph.Using absolute minimum throttle opening and no rapid speed changes...and very little if any brake use except on long very steep grades.

The transmission is a manual 6 speed...but 6th gear is a nice overdrive.Traffic requires braking when people pull in front of you or suddenly slow...this precludes achieving best results.
I tried to drive "normally" today and used WOT 4 times in 256 miles of driving.It got down to 37mpg which caused me to revert to mr hill anticipation and super smooth mode...and the tank ended at 40mpg.Very high head winds today too.

I brought the car home this past I am just getting to know her.Fast and efficient car...I wonder where 31 epa highway comes from?I guess if I alternated between throttle and brakes I could do worse...

redpoint5 06-08-2016 12:11 AM

My Acura TSX has a 10.5 : 1 ratio and the manual says to use no less than 87 PON, but recommends 91 PON. There is an extremely subtle difference in drive feel between running regular and premium, with a little more pep when accelerating. Fuel economy is the same regardless of octane. The difference between the octanes are most easily observed by looking at timing advance; with the higher octane having a significant increase in timing, perhaps up to 10 degrees. I never get codes about detonation because the engine timing adjusts automatically to the fuel used. I've even run as low as 85 PON when staying at higher elevations (5000ft).

Sometimes I alternate fuel fills between regular and premium, with the resulting octane falling somewhere between the two. Plus grades of fuel in Oregon and Washington are simply 60% regular mixed with 40% premium. You can often mix your own and save a very small amount of money.

My motorcycle has an 11.5 : 1 ratio, revs to 14,000 RPM, and Honda recommends 87 PON. Perhaps it runs a little rich to prevent detonation? It doesn't have an O2 sensor, but is fuel injected.

cistercian 06-09-2016 12:33 AM

Today I drove out 100 miles and then back in the mountains...44mpg!
I could have done better...I noticed this morning mileage was not so good...then it hit me 56 degrees was the air temp.Later when the temps rose into the low 70's I observed better mileage.On a hot day in the 80's I might hit 46 or even 48!

That's 41% better than the epa 31 mpg for this car!Whoo hooo!

LeanBurn 08-10-2018 12:46 PM

I just bought a 2013 Civic SI also this week. Fun car indeed, for the fist 1/2 tank I mostly just ripped around in it. The second tank I experimented with different speeds and just getting to know its quirks. On a more EM note...

The weather was perfect (no wind, 59F or 15C) to set a benchmark so I tested the fuel economy on the way to work today and driving conservatively as I would have done in the Corolla, cruise set to 91kph or 56.9mph for my commute and from door of home to door at work (42 miles or 67km)...I attained:

46.12 mpgUS or 5.1 L/100km or 55 mpgUK !!

Baltothewolf 08-10-2018 08:25 PM


Originally Posted by California98Civic (Post 515827)
Not bad at all. This is a manual transmission, yes. No turbo on the Si I believe. What techniques were you using?

Not that gen, no. The 10th gen (current gen) yes.


Originally Posted by MobilOne (Post 515829)
And out of curiosity, why the Shell premium?

My buddy has a 13' Si as well. It pings under heavy load on anything lower than 91.

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