In light of the ridiculous gas prices in California, I am considering switching to 89 instead of the 91 ($3.55/gallon). I am aware of the fact that it may hamper performance, however, I only use the car for daily driving and at this point am a lot more interested in cutting down my gas bill. Are there any other drawbacks to using lower grade gas? The motor is a 2000 USDM GSR.

TIA

 

It won't hurt the engine, but the car will perform sluggishly. My father filled my GSR with 89 octane once and it ran like a turd.

 

Unfortunately that's what I expected to hear.

The motor I have is in a 2000 Civic hatch, running on stock Si rims and Azenis (205/15/50). I am driving it very conservatively, hardly ever hitting vtec, and staying under 80 most of the time. The last 2-3 tanks of this kind of driving I can hardly get anything over 25-26 mpg. Is this normal? For some reason seems very low to me.

PS the highest I ever got in all-freeway driving was 31mpg at about 70 - 70mph.

 

What ECU are you running? If there is no knock sensor, you could have a problem. The stock P72 ECU has a knock sensor.

 

I think for GSr you would want to go 91 cause it says "Premium ONLY" ont he cluster

here is a segment where a similar topic was discussed.

1. In an engine designed for 91 octane, switching to a lower octane may be compensated for by the ECU. However, there is almost always a loss of efficiency in mpg by doing this. At about $3/gallon, the savings are only about 6% by going from 91 to 87. Many cars will see a reduction of 5-10% in mpg, thus negating all savings from the switch.

2. Unless the manual actually says 91 recommended, but 87 can be used, he does indeed run the risk of damaging the engine from pre-ignition.

3. If anything, it makes even less sense now to go to a lower grade. Back when gas was $1/gallon, the price steps between grades were still usually 10 cents. Thus, going from 87 to 91 would mean a 20% increase in fuel costs. With costs hovering around $3/gallon, and those same 10 cent price steps, the increase is now only 6.7% of your fuel costs.

Use what the car is designed for. A high compression engine needs something that is more resistant to detonation. That something is a higher octane gas.

Put a lower-than-recommended octane in your engine, risk engine damage.
Put a higher-than-recommended octane in your engine, risk incomplete combustion.

 

The ECU should compensate for the change in octane and will adjust the timing accordingly.

 

Since I bought my GSR used, I dont know what the fuel capacity is. is it like 12 something?

 

Thanks for the responses gentlemen, I am going to stick to 91 and bite the bullet on the costs. I am still puzzled as to why I am getting such low MPG, but I've been doing some research and am going to take a couple of steps to try to fix it.

By the way, regarding the tank capacity - the 96-00 Civics are listed at 11.8 fuel tank capacity. Believe it or not, I filled up a month ago (after riding with a light on for 2 days, had absolutely no time to go fill up), and the pump meter said 12.3 when I filled it up.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dynamo &raquo;</TD></TR><TR><TD CLASS="quote">By the way, regarding the tank capacity - the 96-00 Civics are listed at 11.8 fuel tank capacity. Believe it or not, I filled up a month ago (after riding with a light on for 2 days, had absolutely no time to go fill up), and the pump meter said 12.3 when I filled it up. </TD></TR></TABLE>

Gas stations can scam consumers by pressing a button to increase the indicated quantity. It is highly illegal. If that happened to me, I would be calling 911 to report the crime.

 

I don't use high octane pump gas for power. I use it to prevent detonation in an engine that has 12:1 static CR. Higher octane just slows the burn process down. If you use it because you think it is for power, then indeed you are fooling yourself.

Some car models require you use higher octane fuel (EVAP system reasons). Check your owner's manual.

As far as I know, there is no car that purely combusts without incomplete burn byproducts. If you know of one, let me know.

Use higher octane for the intention it was designed for: less detonation...not for making power.

 

it is for higher power because you are delaying the point of combustion... giving yourself optimal conditions for better/higher power

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by greenleech &raquo;</TD></TR><TR><TD CLASS="quote">I don't use high octane pump gas for power. I use it to prevent detonation in an engine that has 12:1 static CR. Higher octane just slows the burn process down. If you use it because you think it is for power, then indeed you are fooling yourself.

Some car models require you use higher octane fuel (EVAP system reasons). Check your owner's manual.

As far as I know, there is no car that purely combusts without incomplete burn byproducts. If you know of one, let me know.

Use higher octane for the intention it was designed for: less detonation...not for making power.
</TD></TR></TABLE>

In a properly designed engine, higher octane yields more power. Retarding the timing to compensate for knock results in a loss of power. Technically, you could tune a GSR engine to run on 87 octane by enriching the air:fuel ratio. The catch is that the mixture would no longer be stoichiometric and the catalytic converter would be damaged. A stock GSR running less than 91 octane at an altitude anywhere close to sealevel will experience a power loss due to timing retardation by the ECU.

The octane rating and the EVAP system have nothing to do with each other. The EVAP system never sees combusted products, it simply stores gasoline vapors from the tank. Are you confusing the EVAP with an EGR, which our cars do not have?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by greenleech &raquo;</TD></TR><TR><TD CLASS="quote">I don't use high octane pump gas for power. I use it to prevent detonation in an engine that has 12:1 static CR. Higher octane just slows the burn process down. If you use it because you think it is for power, then indeed you are fooling yourself.</TD></TR></TABLE>

Sounds like quite a bit of Bs..

I guess that means all those high boost cars should run lower octane, since they won't make more power with better gas.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dynamo &raquo;</TD></TR><TR><TD CLASS="quote">The last 2-3 tanks of this kind of driving I can hardly get anything over 25-26 mpg. Is this normal? For some reason seems very low to me.

PS the highest I ever got in all-freeway driving was 31mpg at about 70 - 70mph.</TD></TR></TABLE>

Your mileage sounds absolutely normal. That's about what we get on our GS-R - 24-25 mpg for mixed local and highway driving, and 29-32 mpg on a long trip.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Solscud007 &raquo;</TD></TR><TR><TD CLASS="quote">Since I bought my GSR used, I dont know what the fuel capacity is. is it like 12 something?</TD></TR></TABLE>

It's 13.2 gallons.

You really need to get an owner's manual for your car. You can buy one here.

 

Everybody has good points. The car will deff. run bad, gas mpg might be going down, also you'll prob be seing a CEL if you dont already have one

 

sell the gsr and get an ls

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Homestar Runner &raquo;</TD></TR><TR><TD CLASS="quote">I hope you guys realize the price difference between premium and regular grade isn't that big a deal. Its $0.20 more per gallon, and in a approx. 12.5 gallon integra tank that is 3.55 x 12.5 = $44.38 and 3.35 x 12.5 =$41.88......Cough up the extra 4 bucks you bum..... </TD></TR></TABLE>

think about it in the long run

 

its a few extra bucks a week for safety of the motor..come on...but prices are ridculous, i've been stayin out of boost as much as possible

 

it doesnt do anything performance whise except lower gas mileage