Effects of various octanes?

1FSTBRD

Registered User
I've ran 94 octane in my car, mostly, but I decided to drop down to 92 or so. The car feels like it pulls harder with 92, though the 94 seems like better insurance. What have you guys noticed with yours, in terms of performance, issues and even dyno results with a mostly stock-ish car with bolt ons (ie: no Magnum Powers stuff)?
 
Actually, yes. Muscle Mustangs did a article on octane and basically said, running a higher octane than you need is a waste and can slow you down. Lower octane has a faster flame speed. Problem being from what I understand, that you cant take advantage of the longer duration flame without adjusting timing along with a bunch of stuff I can't remember.
 
The biggest thing to watch out for is, that the lower octane, if it causes preignition, will cause the knock sensors to go off - which will pull timing and enrich the mixture a bit more.

The timing pull will kill the performance gain of the lower octane quickly.

So - it's a fine line. If you ever find it, be sure that it will shift depending on the temperature of the air, the actual air pressure, and how hot the motor itself is, along with how carboned the pistons and valves are.

RwP
 
the fuels octane rating is its resistance to burning, comparing apples to apples it does not effect performance at all

if you went to 92 octane and noticed a power increase then your assumed 94 octane is not what its advertised

running 108 or even 120 octane will not increase power any more than running 92 octane, the fuel in itself won't make any difference in output given the same composition, ignition timing and fuel ratio

a higher octane fuel will allow you to run more ignition timing as compared to a lower grade fuel
 
If you have mods, most likely you are running full knock retard already. I'd be a lot more worried about AFR. 94 probably has a high percentage of ethanol which is likely leaning you out.
 
the fuels octane rating is its resistance to burning, comparing apples to apples it does not effect performance at all

if you went to 92 octane and noticed a power increase then your assumed 94 octane is not what its advertised

running 108 or even 120 octane will not increase power any more than running 92 octane, the fuel in itself won't make any difference in output given the same composition, ignition timing and fuel ratio

a higher octane fuel will allow you to run more ignition timing as compared to a lower grade fuel

Good points. I had asked a similar question last year here after i'd got my SC about what octane point the knock sensor starts to pull timing with detonation/ knock, but I am still curious at what octane rating it becomes overkill for a fairly stock SC, where the octane becomes a hindrance since it actually contains less burning energy. Dave has a good point in that the 94 octane likely does have a high amount of ethanol in it.
 
Well, I did a little research on the butt dyno :D--while the exact starting points don't line up, you get the picture.......the lighter strip is with 94 octane; the darker strip is with 91. So I would surmise that 94 is overkill, but it may still provide better overall detonation protection, who knows?

burnoutmarkscomparisonbetweenoctanes.JPG
 
I would say so.....the temperature was a chillier spring day, and the car was driven the same amount--driven to get the tank low, and then filled up to about the same amount in the tank with 91 and then let the car cool down, then driven more so that the engine and tires would be at the same temps as the first peel out. Obviously, it's tough to know what exact octane is in there because of gas stations being off on their ratings a little bit and of course, the real octane after filling a gas tank that isn't totally dry (this likely might be a 92 octane as a result of a blend), but it surprised me at the difference in the marks that it left. I've felt like experimenting with different fuel brands (maybe Shell V Power 91, as well) to see what happens, as well.
 
Last edited:
Cop dyno..... because if you get caught their numbers are the only ones that matter :)

Heh heh.....too true! We also get charged by the foot on tire marks left on a public road. I'd be in the poorhouse after this one. :D
 
Back
Top