My 99 Si Is getting 260-280 miles per 10 gallons so roughly 28 mpg.

there is no check engine light

i have a short ram intake, and dc headers, stock exhaust.

the car is not lowered and running on stock si rims.

i drive city/hwy

5w30 redline
redline MTL
new wires

i need to adjust the valves...

post up what your EM1 gets per gallon...

 

I get about 340-360 miles to a tank, with my supercharger.

 

About the same. What do you expect 44mpg?

 

no, but i hear of some b16's getting flogged all week and still putting out 35mpg

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ls_dx &raquo;</TD></TR><TR><TD CLASS="quote">no, but i hear of some b16's getting flogged all week and still putting out 35mpg</TD></TR></TABLE>

That's usually how it works, 1.6L is not a lot of displacement at all.

Most of the new Audi V8's and such are still raking in high teens to 20/23mpg off the highway . That's just b/c technology has made them more efficient since most of the decade or half decade old civics.

It has a lot to do with weather conditions believe it or not. Any precipitation at all makes it harder for your vehicle to pull - making you lose more mpg to keep up the same speed.

Also, same goes with air friction, windy day = lower MPG.

You might claim these things are small, but on a rainy day, when you probably aren't using CC, and it's windy out, they all kinda add up. Not to mention if it's cooler out, your engine uses more gas when it's colder (it performs better...but it also uses more fuel accordingly).

Never-the-less, I feel 28mpg is pretty low if you're on the highway.

I've been pulling bad mpg's lately too, about 30 around town when driving VERY economically, and about 30 on the highway (same speeds I used to get 36 on the highway at).

Although my situation is kinda different b/c I have a 43 CEL (Fuel supply system) and nobody can figure out what the hell it is - so that might have something to do with mine.

Though in any event, you'd be surprised, lots of things can contribute to worse gas mileage in terms of weather conditions.

If you wanna try anything out, change the fuel filter, do a tune up (basic **** like that).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by my_slow_civic &raquo;</TD></TR><TR><TD CLASS="quote">I get about 340-360 miles to a tank, with my supercharger.</TD></TR></TABLE>

The thing about turbos or superchargers is they give you BETTER gas mileage when you go easy on 'em/drive normally. Though they can really drain you if you hammer on 'em.

Now I'm sure you drive normally, you'd be blowing smoke up his *** if you claimed you got 36mpg while beating on a supercharged B20.

 

hey man... trade me for my 97cx and you can get 53mpg!!! lol

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Syndacate &raquo;</TD></TR><TR><TD CLASS="quote">

The thing about turbos or superchargers is they give you BETTER gas mileage when you go easy on 'em/drive normally. Though they can really drain you if you hammer on 'em.

Now I'm sure you drive normally, you'd be blowing smoke up his *** if you claimed you got 36mpg while beating on a supercharged B20.</TD></TR></TABLE>


If I acted like an *** while driving, I'm sure it will go down. Even after a four hour dyno session, I still picked up 320 miles on the tank.

Never really changed with the addition of the supercharger. Furthest I went was 372 miles. I can drive all week, and never see boost. My 30 mile commute each way sees my cruise control set at 67 mph.

Also, not sure where you live, but during colder weather they change the gas mixtures up.

 

this may be a long shot...

but maybe the brand of gas burns quicker/slower..

i use shell 91 premium only

i switched to chevron 91 and seems to be doing a little bit better.. .

170 miles before a 1/2 tank going into vtec 5 times

 

bump

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ls_dx &raquo;</TD></TR><TR><TD CLASS="quote">this may be a long shot...

but maybe the brand of gas burns quicker/slower..

i use shell 91 premium only

i switched to chevron 91 and seems to be doing a little bit better.. .

170 miles before a 1/2 tank going into vtec 5 times </TD></TR></TABLE>

No...

Gases burn the same. How do I know this? My dad used to drive tractor trailers, he found out what he was hauling one day was beads...a truck full of beads, so he asked what the expletive are they all for?

Turns out all the gas comes generic, and companies add beads to the gas to get it to turn colors, like exon was using a blue bead or red bead, shell was using a diff color, etc. Sorta like branding cattle.

There's absolutely NO need to use 91 octane. People are under a horrible misconception that if you use higher octane fuel, you will get better MPG and your car will last longer. This is very inaccurate. Higher octane only has to do with the tolerance level the fuel could take before pre-igniting.

A stock honda calls for 87 octane gas.

If you soup up the compression eventually it's going to pre-ignite and you're going to need 89 or 90 octane fuel. That's the only role that octane plays .

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by my_slow_civic &raquo;</TD></TR><TR><TD CLASS="quote">


If I acted like an *** while driving, I'm sure it will go down. Even after a four hour dyno session, I still picked up 320 miles on the tank.

Never really changed with the addition of the supercharger. Furthest I went was 372 miles. I can drive all week, and never see boost. My 30 mile commute each way sees my cruise control set at 67 mph.

Also, not sure where you live, but during colder weather they change the gas mixtures up. </TD></TR></TABLE>

so i assume you have vortech supercharger then

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Syndacate &raquo;</TD></TR><TR><TD CLASS="quote">There's absolutely NO need to use 91 octane. People are under a horrible misconception that if you use higher octane fuel, you will get better MPG and your car will last longer. This is very inaccurate. Higher octane only has to do with the tolerance level the fuel could take before pre-igniting.

A stock honda calls for 87 octane gas.</TD></TR></TABLE>

Except that a 1999-2000 Civic Si calls for 91 octane ... which is what the OP drives.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eran &raquo;</TD></TR><TR><TD CLASS="quote">

Except that a 1999-2000 Civic Si calls for 91 octane ... which is what the OP drives.</TD></TR></TABLE>

Ah yes, I was referring to an older car.

I was making a point.

The point is simple, in and of it's stock form, a car can usually get away with lower octane.

The compression of the B16 isn't terribly high, I wouldn't be surprised if you could get away running 89 octane.

****, you could probably use half 87, half 91 w/o it pre-igniting.

Though my point is simple, octane is only for combustion purposes, other than that, it doesn't increase the longevity of your motor, it doesn't get you better MPG, or anything like that, I hate those rumors. As for different brands of gas, you will NOT get better gas mileage by going to shell instead of exxon.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Syndacate &raquo;</TD></TR><TR><TD CLASS="quote">The compression of the B16 isn't terribly high, I wouldn't be surprised if you could get away running 89 octane.

****, you could probably use half 87, half 91 w/o it pre-igniting.</TD></TR></TABLE>

Point taken, I still like to do what Honda recommends. It's their RnD I trust, not their brand name.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Syndacate &raquo;</TD></TR><TR><TD CLASS="quote">Though my point is simple, octane is only for combustion purposes, other than that, it doesn't increase the longevity of your motor, it doesn't get you better MPG, or anything like that, I hate those rumors. As for different brands of gas, you will NOT get better gas mileage by going to shell instead of exxon.</TD></TR></TABLE>

Debatable. I know for a fact that certain gas stations in my state add higher amounts of ethanol to their gasoline mixtures, almost to the level of "gasahol."

ARCO, Safeway, 76, and CostCo add extra ethanol. Chevron, Shell, and Texaco do not.

Needless to say, I don't fill up anywhere else but Chevron if I'm near home.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ls_dx &raquo;</TD></TR><TR><TD CLASS="quote">no, but i hear of some b16's getting flogged all week and still putting out 35mpg</TD></TR></TABLE>

I'd say most of the people out there do not figure gas mileage correctly and or exaggerate how many mpg they get. I get on average right at 30-32mpg with every B16 i've had all in hatches. I'd say 28mpg is very normal especially not knowing the persons driving habits.

 

I used to get 28mpg on my B18B1 with mostly city when I lived in town. Now, I live 10 miles up the freeway, and 8 miles out a road that the speed limit is a lax 50mph. I've started getting 30+ since I moved.

 

yeah i figured that one stations ethanol content might be more potent than another station... and yes, the b16 requires 91 octane. i dont put it in there because i think ill get better gas mileage, i put it in there because its a relatively high compression engine. thanks for your input guys, lets get some more input ...

 

Does COLD weather increase or Decrease MPG?

Everytime I search people say it decrease mPG but when I think about it cold air is more compact so its more compressed so it should burn better ?
plus cold air will expand more than warm air at explostion temperature?

 

Owned my civc all its life. 70k miles later it still gets the same gas mileage. 27-29 mpg. Don't do much highway driving but 30-32 at most on long crusies (drove from tallahassee to boca raton a bunch of times, 480 miles each way)

Sounds right to me. I live in FL get a lot of rain and my car is stock except no cat and cone filter.

 

I've got a 99 SI too, in Ohio... Your region is probably causing your gas mileage. I recently went on a few trips to Florida... That is 1000 Miles south where I was going.

This is what I noticed. Places are where I bought the gas.
Also note. pure highway miles, no stopping, 70mph 38-3900rpm. My experience the most efficient speed/rpm for the car, as well as the speed limit for most of the trip. BP gasoline, except Florida was Chevron.

Ohio 28-30 mpg (cant remember but it was pathetic)
Virginia 35mpg (hilly too, mountains)
South Carolina 36mpg

Trip back. Florida gas. 44 mpg... yes, 44 mpg. First time I ever went over 450 miles on a tank and just changed because I didn't think it could have anymore.

SC - 36mpg
Virginia - 36mpg
Ohio - 25.....

Moral of the story. While Chevron MIGHT have the better additives that work best for my particular motor. And BP might have the worst. That is not likely, and would not account for the HUGE difference in mileages. However, the temperatures being around winter do. Different season gasoline mixes.

It has always been this way for Ohio, we have had 70F lately... but still, winter gas made my old EX go from 34 HW to 25-26 HW.

 

how is your tire pressure?? i would also look into the air and fuel filters etc.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by my_slow_civic &raquo;</TD></TR><TR><TD CLASS="quote">I get about 340-360 miles to a tank, with my supercharger.</TD></TR></TABLE>

haha...damn nice, if i had a sc id prolly be getting no where those #'s haha.

 

i get about 29 mpg wuth exhaust and header

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by young noob &raquo;</TD></TR><TR><TD CLASS="quote">

so i assume you have vortech supercharger then</TD></TR></TABLE>

I have a ENDYN modified Jackson Racing charger.