91 vs 93 without tune and all stock
 

Is there any difference in car performance and mileage with only 2 octane difference? I'm just curious. I don't know what the dealership filled my car up with, but I've been hitting Sunoco 93 for the past couple days.

Nothing you would notice

Where I am, we have 91 or 94. I can definitely notice a difference. It's not so much about power, or how the car pulls, but it does "feel" better on the 94. I find the throttle response better, and there is less tip-in knock when I run the higher octane stuff.

What? Sure you're not hearing the throttle valve opening as you punch it? It'd be troubling if you were getting audible knock on 91 stock.

http://www.ft86club.com/forums/showp...20&postcount=3

Edit: OT I would fill up with 93/94 if I could, but nothing significant will happen running it on 91 it's whole life. Any impact you notice is likely psychological.

I also noticed the pinging almost every time I blip the gas pedal and its hot outside. Manual says it might ping lightly and its not harmful as long as you don't use less then 91. Personnaly I think they are to close to the edge in many area and we get a car which is almost right but not quite. High compression of 12.5:1 and 2.0L and 200HP = pinging + crickets. Same old, same old. Lots of people will start to say, its only some minor sound, etc.... no damage done....

I'm starting to sound like I'm ranting. I guess I am.

In my area it is very difficult to find 93 Octane. (I have a list of gas stations that have 93 octane saved in my google maps.) For the first couple of weeks I was running 91 Octane and was averaging around 27-28 MPG. When I finally discovered that we did have 93 Octane I've started filling her up with the higher grade stuff. Now I get an average of 30-32 MPG depending on driving habits. I certainly don't drive her hard but when getting on interstates I do tend to rev her up to 5k - 6k RPM. I suspect that if I were to drive her super conservatively then I'd be able to squeeze 35 MPG out of her.

One downside to the 93 Octane that I've run across is that they have ethanol in it (BP "TOP TIER GAS") and I suspect this causes the crickets in my gas pump because I didn't have those crickets when I was filling them up with 91 Octane which did not contain ethanol. (Do gas stations have to state that there is ethanol in the gas? And if they don't state it then does that mean there is no ethanol?) Maybe I'll hop the border to Canada to fill up on some ethanol-free gas and get back to you guys.

I'm positive that what I am hearing is ping. It doesn't happen all the time, and is most common when it is really hot out. I hear it when I blip the throttle on a downshift (which would make one think that it could be the throttle body), or on an upshift when I let the clutch out at say 3-4000rpms, and usually under light throttle. Simply stomping on the gas doesn't cause it. It is not continuous...just a quick snap, then it is done. If I had the ability to datalog, I'm sure I could back up my claim. I have been playing with cars for over 20 years and I know what detonation sounds like.
It is much more noticeable on 91 than 94, and although I don't have much faith in octane boosters (most are snake oil), If I use 94 and some of the 3X Lucas octane booster, it disappears completely. I suspect a tune may help...the stock mapping on these cars is kind of wonky.

Yes the car is designed to run on 93 or better octane fuel to achieve the rated power output. It will run on 91 but you get slightly less power and genenerally slightly less economy although E10 fuels complicate things a bit.

Ethanol has a highr octane rating than pump gass , but its energy content is less hence the slicgh loss in economy with E10 fuels, but this is sometimes compensated by the higher octane rating which allows the ecu to run full ignition advance

The ECU compensates for 91 octane by adjusting a parameter called the IAM or ignition advance multiplier. On 93 this will sit at 1 assuming no significant knock is detected. If the knock sensor detects a certian amount or severity of knock it will decrement the IAM and hence reduce the ignition advance across the entire rpm range. This happens on 91 fuel and IAM will sit around 0.6 or so. Once you fill up with better fuel again no knock will be detected and IAM will return to 1 and you lost ignition timing and hence power will return.

Were not talking huge power loss maybe 10 or 15 hp out of the 200 max.

Running higher octane fuels beyond 93 octane Assuming you are knock free, will not result in further ignition advance as once the IAM is 1 you are running the full timing in the ingnition map. Other factors can effect knock resistance suct has high intake air temperatures so sometimes it can be benificial to run higher octane fuels like track days for better knock resistance under extreme conditions.

Depends also on your local elevation. At sea level it may make a difference but not at high elevations.

I doubt you'd notice the difference because power robbing detonation is inaudible and only occurs at full throttle and full load, at peak torque. At other rpm or part throttle the engine management system will control knock and there is more throttle available which you will instinctively use.

On electronically managed cars any knock you think you hear is merely trace detonation which the ECU reads and adjusts for. I would be astonished if you could actually hear the trace knock before the ECU responds and fixes it but I don't say it's impossible.

The last engine I heard actually knock was in 1982, even turbos which have to knock more or less continuously at peak boost pressure for the boost control feedback loop to work cannot be heard doing so because the knock sensor reacts within three consecutive detonation events or less.

Oh and all Canadian gas has ethanol in it, as an anti knock compound, except for Shell V Power 91 which does not. Shell does not claim any higher octane rating than 91 though. I find V Power 91 to be the best fuel available in Canada for my high elevation. I have used 94 on occasion with no discernible effect even on high boost turbos. Modern engines are fuel tolerant and the power differences are noticable if you drop down to 87 (which really is poor gas for any truly high performance engine but the majority of our market cars are tuned for it, unless your filler cap says use 91 then don't bother.)

No offense but unless you can data log tip in knock. There's no way to truthfully say there is less. Sounds like you are undergoing pure placebo effect. In essence, "I spent more on gas, and it says it's better for the car. So it must be better". Even on my turbo eclipse, data logs show no discernible difference between 91 and 93. That's running a tune off of 93, at 25 psi of boost. Now when you get into 87 and 81....there is most definitely a difference.

I just switch from Shell 91 to Husky 94 and I was able to tell the difference. The engine definitely felt more alive and happier on 94, however the crickets are much worse with the E10

Less, biggest difference I could find evidence for was ~4hp peak. I won't argue that you loose some more under the curve but to imply that 91 vs 93 is 190 vs 200 hp at the crank seems exaggerated.

93 vs 91
http://www.fiestastforum.com/forum/t...ctane-OTS-maps

http://forums.themustangsource.com/f...octane-487398/

87 vs 91:
http://forums.vwvortex.com/showthrea...91-octane-dyno

87 vs 93 seems to give the numbers you stated on a Focus ST:
http://2gfusions.com/index.php?topic=2928.0

I've been running Chevron 94 since day one :burnrubber:

So everyone in California is running underpowered FR-S's? Damn. Glad I'm on the East Coast for one thing. Although the country out there is SO beautiful.