The UK Owners manual states: - “OCTANE NUMBER Select Research Octane Number 95 or higher. Use of unleaded fuel less Octane Number 95 may result in engine knocking. Persistent knocking can lead to engine damage.†This is a lot different form what I have been reading on the PC threads, the engine seem to have the same physical compression ratio, so is the valve timing mapped to give a higher operating ratio? Is the ignition mapping different? Anyone know what is going on here, and what is in the Owners book elsewhere? Jon the Chief
The numbers you typically see posted here on PriusChat are U.S. and Canada numbers. On this side of the pond we don't use the Research Octane Number (RON). We use the Average of the Research Octane Number (RON) and the Motor Octane Number (MON). This octane number is also occasionally referred to as the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2
However, it is worth pointing out that (RON)95 ~ ((R+M)/2)90. This suggests that there different "minimum" standards for the Prius in different regions. I don't know if this is a real difference (i.e. in the engineering/programming of the car) or if it just reflects the difference in the minimum octane gas available in the different locations.
Must be different there than here because here the Prius runs on 91 RON so mapping must be different. I believe 95 RON is the minimum in the UK anyway. I expect to see some pretty impressive numbers from you Jon! Thanks for the EBH tip-off.
91 RON, blimey, you guys must struggle especially in the heat? You're right on the UK's RON as the minimum is 95 but I usually use 99 which is only blended by Shell at their V Power refinery in Cheshire, UK.. If you're feeling REALLY, REALLY flush there is BP Ultimate 102 but it is over two and a half times more expensive than standard 95. For 95 we are presently paying about £4.80 per gallon or the equivalent of $9.60 per UK gallon. And you guys in the US think you pay too much.
In mainland China the offered grades are 90, 93 and 100. I don't know which grading system they use. If I had a Prius here, I would probably trade off tanks of the lower two, and see if 93 worked noticeable better. Last time I checked the price, 90 sold for equiv. USD$3.50 per US gallon.
Just a reminder that higher octane doesn't mean better mileage or a better running engine. To low of an octane and your engine will knock. Too high mileage and power takes a hit, plus you can have trouble with incomplete combustion leaving residue. Tom
