Octane ratings

[eljefino]

Knock control is a feedback thing much like o2 fuel control. They want everything they can get from every drop of fuel, crummy or not, and flexibility beats fixed tables.

Marketing will also get involved, and they don't want some punk hatchback having the same rated HP as their premium sedan. Look at GM making sure the Corvette has a slightly hotter engine than the Camaro a year sooner.

I've seen cars advertised with "200 peak hp" and the fine print reads you need premium to get that. It was something dumb like a dodge stratus.

Also colder air needs less octane, so vary by season. While thinner air needs less as well, that's only for normally-aspirated. Your wastegate controls this via yet another feedback loop.

 

[Swift101]

Originally Posted By: eljefino
Knock control is a feedback thing much like o2 fuel control. They want everything they can get from every drop of fuel, crummy or not, and flexibility beats fixed tables.

Marketing will also get involved, and they don't want some punk hatchback having the same rated HP as their premium sedan. Look at GM making sure the Corvette has a slightly hotter engine than the Camaro a year sooner.

I've seen cars advertised with "200 peak hp" and the fine print reads you need premium to get that. It was something dumb like a dodge stratus.

Also colder air needs less octane, so vary by season. While thinner air needs less as well, that's only for normally-aspirated. Your wastegate controls this via yet another feedback loop.


All good points, I might try 87 in November and see how it feels.

 

[zeng]

Originally Posted By: Jetronic
RON is what on european pumps.... Maybe in asia also?


Yes, Malaysia is RON 95 and RON 97.

Singapore RON 98.

China RON 93 etc.

Japan is RON too I suppose.

 

[dnastrau]

Originally Posted By: zeng
Originally Posted By: Jetronic
RON is what on european pumps.... Maybe in asia also?


Yes, Malaysia is RON 95 and RON 97.

Singapore RON 98.

China RON 93 etc.

Japan is RON too I suppose.


Correct. Also - the US and Canada used the RON before the mid '70s as well. The "100 octane" premium of the 1960s and early '70s in the US was 100 RON and would be rated at about 95 on today's US and Canadian pumps using the R+M/2 (AKI) method.

Andrew S.