Engine Capacity relating to Fuel Octane

[:Exige:]

Ok - another funny argument ... but now they're trying to justify 8-litres.

Ok ... a larger capacity allows lower octane fuels (93) to create more power apparently. Say the original engine was 4-litre ... how much more power would be created if the engine were an 8-litre. Would this change be justified? How much does capacity and fuel octance affect power?

[johnnynumfiv]

A larger capacity would make more power because more gas/air would be coming in. Usually in higher compression motors a higher octane gas is used to prevent pinging. Which in some cases with larger engines that were made back in the 60's had compression ratios over 11.5, so higher octane had to be used.

[:Exige:]

But lets say your bringing an Elise into America. Its made to run on 98 octane. If you had the money, would the power gain be good enough to justify having the capacity doubled? (I dont care if this is possible or not BTW .. its just an example )

["Clevor" Angel]

It all depends on what you do with it. You can have a 5.7litre chevy v8 and make 450bhp or you could have an 8litre viper v10 and make 500bhp, or you could have a porsche 911 motor and make 440bhp, the displacement doesn't really matter but it is the easiest way to make more power on pump gas. I'd say yes, it would be feasable, say you wanted to put a 350 chevy in the lotus, with very little effort you would be making 2 or 3 times as much horsepower, but it would ruin the balance of the car, the advantage of smaller motors: They rev higher and are lighter, and often justify their smaller size with ability.
ps imo, "Theres no substitute for cubic inches!"

[deffenbaugh03]

Does engine capacity have anything to do with octane rating? Like johnny said: engines with higher compression ratio's need higher octane fuel so they don't predetonate. You can have a big capacity engine with a low compression ratio. A large capacity engine does allow more power but really there's not too much importance to how big the engine is. What is mostly important is how well and how much an engine can breathe.

[Juggs]

displacement has nothing to do with the octane rating. simple as that. octane rating is all about the compression ratio

[gregvl52]

Please note in discussion of octane rating that the USA is on a different scale than the UK and Europe. 98 in the UK does not equal 98 in the US.

From wikipedia:

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "normal" gasoline in the US and Canada, would be 91 in Europe.