Quote:
Originally Posted by Maila87
Yes, you are right. Just finded, that AKI in USA is different to other ones used in different countries. AKI used in USA is 4-5 points lower. In other countries using AKI it is between 8 to 10.
Based by twice read this article Octane rating - Wikipedia, the free encyclopedia
Strange, that is recommended RON 98 in Europe - see no difference to 95. |
98 RON is roughtly 94 AKI.
You can get a pretty accurate estimte by taking the RON value and multiplying it by .95 to get the approximate corresponding AKI (i.e., 98*.95 = 93.1; 98 RON = ~93AKI).
Most ECU's have an ignition map that starts higher (for example, after a reset) than you see over the course of driving and pulls timing based on knock detector activity and also transient conditions like air, water, and oil temps. It will add timing back in as conditions change, of course.
So, threotrically, higher is better, at least to a point. You would probably see diminishing returns past 95 AKI /100 RON without a re-tune.
Also as you start creeping into higher and high octanes (well over 100), it gets harder to ignite (especially when cold) meaning potentially fouled plugs, higher emissions, etc. but no more power without a re-tune of the spark maps (unless it was under so much load and such harsh ambient coniditions that it was seeing some knock, of course...)
So basically anything betwen 91 AKI (95 RON) and 95 AKI (100 RON) is good, with 93 or 94 AKI probably being about optimal on the factory tune in normal, but spirited, driving condtions.
If you were never going to put much load on the engine (i.e., drive slow, wihout any sudden acceleration or high speeds), a lower octane would work in a pinch to keep from getting stranded or something, but it's far from ideal or recommended.