High octane petrol - placebo or real difference maker?

You have to understand what octane is there for. Actually octane is not really a higher power fuel. It is a ignition retarder in the fuel. Higher power engine that are designed to work with high octane need it to perform correctly. A low power engine will not see any difference with it or not. But a higher compression engine has a tendancy to self ignite the fuel and that is not good. In a modern engine if the octane is too low and the Knock sensor sense a detonation it will retard the timing and the power will suffer. So yes it can feel a lot different in the proper engine.

I use to have a older engine(429 super cobra jet) that was very fussy on fuel. On 91 it would ping like hell and as soon as I could put Sunoco 93 in it it stopped pinging.

 

My F355 sounds better on 106 race gasoline, however, it makes significantly LESS power.

Octane is in gasoline to prevent preignition, not to make power.
Power is made by increasing the compression ratio up to the limit where preignition gets out of hand (and the engine self destructs.)

 

It's very possible that 91 octane is marginal and the 95 allows the computer to run more timing.

 

We run higher octane in the challenge cars for more performance but most importantly cooler engine temperatures.

 

My guess is the computer can handle a decent range of mappings which allows it to handle of crappy 91 octane fuel here in CA. Everywhere else they have 93, which is optimal for the car. 95 is on the other side of that map, so I woul d think that the car would run slightly better at higher rpms with that fuel. Anything else is wasted unless your ECU has been modified to take advantage of the higher octane - basically greater advance.

 

Any benefit in using the 91 fuel and then adding an octane supplement?

 

I think that's not a bad thing so long as you don't use an ether product. Won't hurt. Don't expect a noticable gain in performance.

 

Keep in mind octane is NOT a power booster. An engine built to be used with a certain octane number need it to perform like it was meant to be because of possible detonation problem without it.
An engine that was engineered with low octane will not perform better with higher octane.

Do a test on a long run with and without octane supplement and compare performance and fuel economy. If you don't feel or register any difference you're wasting your money.

 

I would tend to stay away from them as they do more harm to Cats then anything. I know an occasional can of techron will help clean the injectors.

We run some upper engine lubricant to counter the poor quality gas we have similar to what diesels run. Helps keep all the goodies & seals nice and happy happy.

 

it's an interesting difference a pond makes. Our basic octane is 95. super is between 97 and 99 depending on which brand. shell Vpower is now 99. Most owners will use the higher octane, but I presume we have the same compression? Never tested the difference on track or test conditions so cant comment on performance,

 

I do use injector cleaner now and again Tim. What upper engine lube do you put in?

Henry

 

The octane rating system is different in the US. As a rough estimate add 4 points to the US value. Manual for the 355 says 95 octave. US high test is typically rated at 91 or 92 which goes to 95 or 96.

 

Anyone will help. I been using them in the high strung motors and my street cars forever since we went to unleaded fuels. I used to pop several motors a year and this helped greatly with longevity.

"upper cylinder lubricant" Lucas is good stuff. I use optilube products also. I know so may that just use a 2 stroke oil with great results. Basically anything with sulfur helps.


Read up a bit on it, ignore the bad stuff haters say