What is RON

What do the numbers etc actually mean?

Cheers

RON is Research Octane Number (Used mostly in the UK)

MON is Motor Octane Number ( USA use this and is far more applicable to high performance/turbo engines)

AKI (Anti-Knock index) is also used by race engineers and is (RON + MON) divided by 2.

As far as I know, in the States they use AKI Charlie.

As far as I know, in the States they use AKI Charlie.

MON is the USA standard, shown on all pumps and race fuel containers. I worked there for Kawasaki racing a few years ago.

Informative link here.

Informative link here.

So why do certain cars/supras need a certain number?

Because the engines have been designed and mapped to run on particular octane level fuel. If different rated fuel is put in you're likely to get poorer performance and possible leaner running.

Because high performance cars try to extract the most amount of energy out of as little fuel as possible. They run aggressive spark advances, high compression ratios or boost pressures, and they get hot. They also (speaking from the OEM perspective) have fuel economy targets to meet, so they try to do this with as little fuel as possible.

The octane rating meausres the fuel's ability not to go bang before the spark plug tells it to (which is detonation, or knock). High in-cylinder temperatures and pressures make more power but they also create conditions where an engine will detonate.

Typically, an OEM will map the fuelling and spark so that an engine will not knock when it is run on normal pump fuel (95 or 98RON), but they will cut it pretty fine so as to get the maximum power out of it. If you take a car and start to tune it (especially by upping boost, which is what 90% of the performance mods talked about on here are based around) then you go further into the regime where knock will occur.

Using a fuel with a higher octane rating is a simple way to extend the engine's knock resistance without having to run so rich that power suffers.

MON is the USA standard' date=' shown on all pumps and race fuel containers. I worked there for Kawasaki racing a few years ago.[/quote']

They show MON figures alright, but when they say 'pump 91 octane' they mean AKI=91, don't they?

 

In all my dealings with americans that's the impression I had. The first eye-opener was when I used a '93 octane' map and got straight to DetLand. Turns out it was AKI they meant all along.

 

Even on SupraForums it is the average MON and RON that they mean, but if you're 100% certain then I could be wrong...

 

(Charlie, by the way today I finished the 'wet compression' setup, curious to see how the supra's split turbo intake behaves...)

i think the ron rating is simplified as the fuels heat transfer ability, and how breakable the molecular bonds are between the particles.

The higer rons fuels burn alot slower(stronger bonds), and use up alot of the original spark heat to ignite them, thus the chamber runs cooler, and in most cases so slow that ign need upping to get peak cylinder pressures back to optimum crank angle ...

I thought that the US mon rating is (RON+MON)/2 = US MON rating????

Aye, higher-octane fuels tend to burn slower and have lower calorific values as well.

US fuel is very oxygenated too, so comparisons are not very straightforward.

They show MON figures alright, but when they say 'pump 91 octane' they mean AKI=91, don't they?

 

In all my dealings with americans that's the impression I had. The first eye-opener was when I used a '93 octane' map and got straight to DetLand. Turns out it was AKI they meant all along.

 

Even on SupraForums it is the average MON and RON that they mean, but if you're 100% certain then I could be wrong...

 

(Charlie, by the way today I finished the 'wet compression' setup, curious to see how the supra's split turbo intake behaves...)

Maybe its changed now, I was working there in the early ninetys and it was all MON at the gas stations then. Think 92 MON=97 RON (as a rough equivilent, MON has a totally different definition of knock and is far more applicable to modern engines)

(Charlie, by the way today I finished the 'wet compression' setup, curious to see how the supra's split turbo intake behaves...)

Are you talking about pre-compressor fuel injection? Interested to hear about the results. We've played with that too, albeit on a supercharged engine.

yes mate, it's one of my favourite experimentations.

Gets a bit involved though.

You can shift the whole compressor map to the right, on-the-fly hybridisation as I call it.

(there *are* gotchas, say you also shift the surge line as well as the efficiency islands).

Well, you ought to see some pretty big gains if you get it set up right.

I've seen them already mate, just not on the Supra.

Anyway, I'll do a writeup on my site eventually.