Octane question

[onequick99si]

I have a 99' civic si that has a b16a2 1.6 liter engine that redlines at 8200 rpm, I did some searching on google and found out that the compression is 10:2:1. In my owners manual it recommends that I run premium gas, would it hurt my engine if I ran 87 or 89 octane gas?? I have heard people in the past say that for these engines one shouldn't use anything less than premium fuel is this true.

The gas price's in my area are getting crazy and I would really like to run a lower grade of gas, oh and by the way I use fp60 with every fill up!

Thanks in advance!

Don

 

[Shannow]

Don,
that depends entirely on the Engine Management System.

If it retards with lower octane, then run what your wallet and desire for speed dictate.

 

[BlueWorld]

It does depend on the ECM, put you'll have to monitor MPG with different grades.

It could easily be the case that 87 could wind up costing you more than running 89 or 91 because of the ECM de-tuning.

 

[Dr. T]

The owner's manual should spec the min. octane. Then spike it with FP and you will be fine.

 

[onequick99si]

Hey everyone thanks for the input! I was looking through my manual and found this, it reads (U.S. Si model and Canadian SiR model) use a premium unleaded gasoline with a pump octane number of 91 or higher.

If you are unable to find premium unleaded gasoline, you may substitute an unleaded regular gasoline. The engine will compensate for the lower octane, but you may notice a slight decrease in power as a result.

I guess this means I can run reg. gas?

The last time I filled up I went ahead and used reg. 87oct gas and didn't hear any pinging nor did I feel any power loss, I added 1oz of fp60 per five gallons also! Oh and the MPG stayed at about 33.

Don

 

[uconn1150]

"If you are unable to find premium unleaded gasoline, you may substitute an unleaded regular gasoline. The engine will compensate for the lower octane, but you may notice a slight decrease in power as a result."

Once in awhile is ok, but I wouldn't permanently do it. I would experiment with maybe the 89 and FP, but I WOULD NOT do it with the 87.

With the high price of all grades of gas, 20 cents more more the good stuff works out to only $2 a tank, which is 300 miles--thats .67 of a CENT per mile.

Insurance is what costs us!

P.S. Being much colder, the 89 SHOULD suffice with FP. During the warmer months I'd go back to the 91. Lower temps = lower octane requirement

 

[uconn1150]

I have a B16 as well. If you dip the Octane, you'll lose performance (and not only "go" performance, you will lose mileage as well). The best thing to do is to "suck it up" and use the premium and then continue to use the FP to potentially gain more mpg.

By the way, you should be getting 30mpg with that B16--unless you redline or VTEC it a little too often.

 

[Ken2]

Don,
Can you run at least 3 tankfuls of each gasoline on repeatable trips? You need to get the actual cost of the fuel per mile. I expect you will burn more low octane gas and not have an actual savings per mile.


Ken

 

[onequick99si]

Ken2 wrote:


Don,
Can you run at least 3 tankfuls of each gasoline on repeatable trips? You need to get the actual cost of the fuel per mile. I expect you will burn more low octane gas and not have an actual savings per mile.


Ken


Yea I'll try that! The last tankful was with 87oct and fp60, the MPG was very close to what I got with premium 91oct gas.

 

[onequick99si]

Great info thank you!!!

 

[glennc]

I'll second the advice on temperature being a factor. If the engine compensates for the lower octane, there is probably no threat of damaging it with 89 or with 87. Track your mileage, and you will learn whether the cheaper gas is more cost effective. The price difference (87 to 91) is about ten percent, so you'd have to lose 10% of your mileage to make it a bad deal.

I'm guessing that in winter and for routine driving, you won't see any difference. In summer and heavy traffic, you will. Once you learn how the car behaves on the lower gas, you can fill up each time based on the driving you'll be doing, and the time of year.

- Glenn

 

[Toysrme]

No engine can compensate for octane before hand & solve pre-ignition. No engine knows what's in the tank.
It's a continual cycle of the engine management trying to run the factory timing for current conditions VS interpreting detonation via knock sensors. That also means that under such conditions there will always be cycles of detonation regardless of what the ECU is doing. You simply might not realize it.
It's not a big problem for stock engines. Most of them are conservatively tuned & overbuilt at *least* enough to survive mild pinging over a long amount of time.
I still wouldn't push your luck. If you're going to drop octane lower than the OEM recommends, operate the engine in an engine friendly way. You're just inviting problems wringing out an engine that has mild pinging, regardless of how the computer reacts to detonation as (going back to the first point).

The computer will always lag behind the onset of detonation, the severtiy of detonation & when "adjusted" will step back into detonation every few firing cycles if the conditions have not improved.


I would find a way to do it safely if you plan on doing it long term & can't change your driving habits & general engine operating conditions enough to keep it 100% safe. Retard ignition timing & deal with a slight power & economy loss. (However you can, crank position sensor, distributor, or piggyback)
And/Or try running slightly richer.
(Both of which defeat part of the purpose of using cheap gas)