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Message: <blockquote data-quote="shiroitenshi" data-source="post: 1064336022" data-attributes="member: 27518">wow long time never enter. Busy with work. AFAIK whether or not your car can run ron95 is based om dynamic compression ratio, which is usually 7-8.5 or more, depending on what fuel you run, down from your static compression ratio of 9-13+. how dynamic compression is derived is based on your cam duration and timing, its a moving value, which changes depending on cam profile from 1k rpm to 9k rpm so don't think that 7-8.5 is a static number, thats why its called a dynamic compression ratio. Also related to why vtec has two cam profiles to maximise power output, and also why adjustable timing like ivtec is good for low end power, because it can keep in that dynamic comp ratio at a good value throughout the rev range.Head design also plays a part in enabling you to run higher compression. clover leaf designs are supposed to do that, but due to cost and negligible performance increase, most auto makers just don't use it.Final part is is how ignition timing works to help reduce knocking, since increasing dynamic compression induces knocking due to high combustion pressures, what we do is retard timing to reduce that pressure, so if you fill up with 95, and find knocking, backing off the static ignition ny a degree or two can sometimes help, but reducing combustion chamber pressure = less power, and also... more heat.some old volvos actually have a jumper at the distributor, that jumper retards the ignition or advances the static ignition timing by a few degrees depending on what fuel you put in.A good question is why car manufacturers don't simply make high compression and big duration cams and make big power? Valvetrain wear. When you run big cams, don't expect high mileage out of it, 100k or more, you need to probably replace the valvetrain.so if you have to run Ron95, and find knocking, you can retard a degree or two on the distributor, and drive it around.. well mostly...Sent from my GT-N8000 using Tapatalk 2</blockquote>

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