In an internal combustion engine, the measurement of the difference between cylinder volume at BDC and TDC. This is the ratio of the maximum-to-minimum volume within the cylinder, between the piston and cylinder head, containing a combination of fuel and air being compressed. A high compression ratio results in more mechanical energy that an engine can squeeze from its air-fuel mixture. High ratios place increased oxygen and fuel molecules into a reduced space; thus, they allow increased power at the moment of ignition. Compression ratio is a single number that can be used to predict engine performance.
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so to answer Sherry’s question a lower octane rating is best for her low compression engine, I don’t know how they measure octane where she is located but in the states, 92 octane is high and 85 is low, my 2002 suzuki hayabusa had a CR of 10.5:1, thats considered low in the states so it ran best on 87′ my 2005 GSXR1000 has a compression ratio of 12.5:1 and is considered a high compression engine, it likes 92+, race bikes can go as high as 13-14.5:1 and they require a race fuel additive that bumps the octane to as high as 110, then there’s 118 octane for CRs as high as 17:1… staggering!
in regards to compression ratio vs octane rating it basically goes something like this, and you CAN research it. gasoline is designed to ignite at a certain compression ratio at a certain time as in ignition timing, a higher octane fuel is designed to “optimally” ignite at a certain compression ratio (CR) and spark detonation timing, for instance if you take a high compression performance vehicle and burn a low octane you may hear a pinging, that is the fuel pre-igniting because that lower octane fuel is formulated to ignite at a lower compression, if you proceed to the other end of the spectrum, high octane fuel/low compression engine you will not achieve a maximum efficient burn, so with no mods you should always refer to your owners manual for the octane required, the octane they suggest WILL be the optimum and best for your vehicle there are other factors involved, also, higher octane does not equate to better quality fuel in most cases, you can get good or bad in all octane ratings..
Hi, I want to ask, a small 150cc moped, liquid Cooled with compression ratio of 10.4 is suitable to used RON 95 or RON 97?
In my country they are two types of RON grade, 95 and 97 only but the price different Ron 97 1/3 higher then price Ron 95….
Sorry to say this mate but higher octane gas lowers the burn temp. You might be thinking that wrong or maybe your talking about something diffenent and i didnt catch on. From what i know the higher the octane the lower the burn temp and the less likely youll get preignition
If you are talk what im thinking your talking about remember this its better for the engine to run cooler
Right Brandon. I’ve been told that higher octane gas requires a higher burn temp. But I’d amend the illustration to say “pour a 100 cc’s of AIR into the sparkplug hole and compress it” since water is a liquid and liquids don’t compress (= hydraulics)
But to Nicky: I would think a compression ratio lower than spec could be due to leakage of the gas-fuel mix from the piston rings to the cylinder wall(s), or maybe insufficient air intake at the valve. You’ve already verified good spark I’ll assume. There’s likely other explanations I’m not savvy to.
What will happen if your compression ratio is supposed to be 11:1 and you are only getting 9-10?
While This Definintion make sense to me now I had to go else where to get a basic Idea what compression ratio was this is what I got that helped me
Here’s a definition from Motorcycles Forum moderator, Bill Wood:
“Think of Compression Ratio this way: When the piston is at the bottom of the cylinder, say you could pour 100cc of water into the sparkplug hole (both valves closed) and it would be full. When the piston is at the top of its stroke, you can only pour 10cc of water into the hole to fill it. The compression ratio would be 100 to 10 or 10 to 1. That’s about as easy to understand as I can make it. Oops, forgot to say — Higher compression ratios (in general) will let the engine make more power, require higher octane gas and be harder for the starter to turn over.”