Stew Pidasso

A while back there was a dispute on using the cheap low octane gas.I found this article on a Nissan forum.I hope this will settle any disputes.
http://www.dynospotracing.com/octane.htm
Edit: My theory on the low vs. high octane fuel is as follows.
If you use low octane gas you will get less gas mileage and less power due to the engine retarding the timing to accomodate the lower flash point of the fuel (detonation=pinging and knock). When you use higher octane fuel, the engine will detect more hydrocarbons in the exhaust (unburnt fuel-oxygen sensor) and advance the timing and lean out the engine more in order to run at it's peak efficiency. Advance timing= more power and low end torque, lean it out and you get better fuel economy.
These are my thoughts on the subject.Please comment on what you think.
Also, why spend so much on a car and then put cheap *** gas in it?


[Modified by Nitz5785, 9:50 PM 8/13/2002]

H23 Power

if the car only requires low octane....9 times out of 10 its pointless to put high octane in it.

the 98-02 v6 was dyno tested to LOSE power all accross the power band when using premium gas.

VERY VERY new engines can detect if premium is being used...ie. 02 civic si and 03 accord...but older engines do not, therefore, unless you advance your timing manually...you're not gaining any power.

you're theory is almost good....except for the fact at WOT the ecu is in open loop mode and doesn't get anything back from the o2 sensor...so when you're trying to go fast...you theory doesn't hold true

H23 Power

vtc is cam timing...not ignition timing

greensleeper

yes. yes it is. I'm an idiot.

H23 Power

even if you were to get better milage...wouldn't the cost difference offset the gains??? just a thought

Stew Pidasso

I really couldn't test it because of my driving habits( they vary but are usually on the lead footed side).I personally don't care about mileage.Using gas is just a part of life and if I use more getting there quicker then ohwell. Timeis more important to me than spending a few extra bucks a week in gas.
01GSR,I'm aware of the open loop at WOT.What I was referring to was normal everyday drivng and fuel economy.And I do believe that the car does lean out the fuel if it detects excessive hydrocarbons, why do you think we have OBDII? Do you think that auto manufacturers will just let all that unburnt fuel out of the exhaust? I'm sure that most cars maufactured today are made for lower octane fuel but more expensive cars (Benz,Bmw etc.) are made for and recommend premium. Either way I will continue to use premium.

zeta_msz_006

I see 2 problems with the test. First of all they didn't specify if the cars being tested was modified or stock. Second the test was performed on 2 different cars with 2 different owners, may be the owner of the 89 Octane car doesn't take care of the car at all, or maybe he has advanced his timing and still using 89 Octane gas which is not recommaned.

Chiovnidca

As far as I know there isn't a sensor that measures hydrocarbon on OBDII, or any other cars. The O2 sensor measure oxygen content but it has no idea if there are any unburned hydrocarbons. All it does is give the ECU a signal so it knows whether it is lean or rich.

formervendor

What is High Octane Fuel? It is yeild number..... if a race car with high compression runs 87 it will ping, knock, and blow up!! Why? Because it is too easy to burn!! With low octane gas it will pre-ignite (burn prior to TDC) a highr octane fuel is harder to burn which allows this motor to reach TDC and take advantage of the high compression. Putting high octane fuel in a vehicle that does not require it is the reverse.... low compression motors w/ 87 or 89 will burn the fuel in proper ratio, adding 91 or higher will overwhelm the spark (smuther the flame) and results in a loss of power, carbon build up, increased emissions, a nasty smell, and an empty pocket book. If The car was meant to run on 87 or 89 there's a reason. Testing has gone into it, it's not a guess or a trick to make you lose power....

Last weekend I drove up to Sacramento from Los Angeles, just prior to leaving we filled up with 87 at Mobil, we got 332 miles to the tank and traveled an average speed of 80mph. before we filled up again. We filled up with 91 before comming home and got 310 miles to the tank again driving an average of 80-85 mph. I find this test a little funny!!! Oh by the way... this test was to show my wife and mother in law the comon mistake made by so many.


[Modified by Duckiller00, 6:52 AM 8/15/2002]

H23 Power

but, take into considerations the new civic si has been dyno tested to gain power because the ecu advances the timing to take advantage of the higher octane.

same with the new accord, an enginer of the v6 engine said you would gain 10 hp an 10 lb-ft by using premium fuel...of course i'll believe that when i see it on the dyno also

but yeah, this is on the new cars...on ours its pointless and hurts more than helps


[Modified by F23 Power, 1:36 AM 8/15/2002]

Razor

for 6th gen and older accords just 87, otherwise you're just making your wallet lighter. im pretty sure on the 7th gens its different, you can use 87 but if you use 91 the ecu will advance the timing ACCORDingly() and you will actually gain hp/tq with the higher octane.

Stew Pidasso

I'm not saying this about accords but about newer cars in general.
Chiovnidca, why do you think an oxygen sensor measures oxygen?It measures oxygen in the exhaust to determine if it is rich or lean.If there is too much oxygen then it is too lean (not enough fuel in the mixture to completely use available oxygen during combustion).If there is not enough oxygen, then it detects that it needs less fuel and leans the mixture out.
http://www.howstuffworks.com/question257.htm

Angry Joe

Very simple: The article is accurate IF THE ENGINE IS DESIGNED TO TAKE ADVANTAGE OF PREMIUM FUEL

If it isn't, you are wasting money. There is no debate. High octane fuel is not cleaner, it does not produce more power and it does not give you better mileage if your engine is designed to use regular fuel. End of discussion.


[Modified by Angry Joe, 9:51 AM 8/15/2002]

KGAccord

If your car was not designed to run on premium like any accord motor it will probably hurt performance. I can also speak from experience that before my swap I ran 93 to get my tank and lines cleared of 87 and it felt sluggish and threw a check engine light a few times. Have you seen the Car & Driver issue which showed a loss in power on the V6 Accord with premium? It says 87 for a reason and that is why my dad didn't buy a Maxima cause he needed 93 octane for it.

Another thing it's called a Knock sensor, f22s don't have it. My H22 does cause it needs premium. This is what will sense good or bad and will advance or retard timing a tad to compensate. This does not mean lets run race gas cause the knock sensor will advance timing, you will need to do that manually.

greensleeper

yeah - take that!!! you big meanie

Chiovnidca

For the most part this is true. But what happens when you get a missfire? The exaust gets loaded with oxygen and the O2 sensor voltage goes low telling the ECU that it is running lean. So the ECU richens the mixture, but the miss is still there and the O2 voltage is still low. So you have an engine running rich but the O2 says it's lean. It also has very high hydrocarbons. (They run like a corncob when this happens.)

I'm just trying to point out that hydrocarbon can't be measured directly.

mrvinyl33

My owners manual says to use atleast 86 octane...so I use 87 and it's all good.

H23 Power

127...everyone knows that...sheesh

KTeller8

i still think it has a lot to do with how you drive..