PSIG wrote: ↑Wed Aug 09, 2017 10:58 pm
Here we go off the tracks again. Aluminum is relatively irrelevant, and in the real world allows perhaps 0.5:1 additional compression, but at the same time by absorbing the heat more readily it reduces the engine output slightly. It's a draw and does not have bearing to what you're seeking. Again, engines (iron or Al) have been produced for public use, with standardized "pump gas" at compressions higher than 12:1 for over 50 years.
This sends us back to the different "compressions" and how they are used. A 7:1 and a 12:1 engine can both be manipulated to run the same fuel without detonation, as the effective compression (not just static or dynamic) can be altered. This is one of the factors that allow the 18:1 Flex engines to run 87 octane gasoline without detonation, and how the "HiPo" engines of the muscle cars could run factory 11:1+ on pump gas. Yachtsman, all the talk of static compression ratios is not of much value until you read and understand some of how it actually applies.
David
I talk of static compression by preference most people understand it, it is a simple concept, it is what it is. Dynamic compression depends on the camshaft and timing and is more complicated. It's possible that two engines with the same static compression could have very different dynamic compressions. Probably unlikely, but it is possible
The static compression ratio of an internal combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines.
In a piston engine, it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.[1]
For example, a cylinder and its combustion chamber with the piston at the bottom of its stroke may contain 1000 cc of air (900 cc in the cylinder plus 100 cc in the combustion chamber). When the piston has moved up to the top of its stroke inside the cylinder, and the remaining volume inside the head or combustion chamber has been reduced to 100 cc, then the compression ratio would be proportionally described as 1000:100, or with fractional reduction, a 10:1 compression ratio.
From Wicopedia compression ratio