gas octane rating
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About Compression
There is a significant consumer demand for higher-compression head kits. We asked Spaulding about why a person would buy and install one and what kinds of fuel changes those kits require. "You would do this to increase performance," he said. "This subject is as difficult to answer, if not more, than the fuel discussion. Every type of motor is different in its reaction to this change, and you almost need to be the designer or developer to know if there's a gain in performance by adding compression to a particular engine. I'll try to explain.
"You know you need to have correct fuel for your chosen compression ratio, but not overkill on octane. So you have selected that, and hope to see a gain by adding compression. In most cases, higher compression ratios will give you some gains in low and mid range acceleration or pull. Top speed is another issue."
Spaulding went on to explain that a high dyno number isn't always indicative of how an engine will do in the real world. "Higher compression ratios may not be faster, and in some cases may slow top speed.
This happens because the increased cylinder pressures generate more heat due to, among other things, higher compression and ignition timing advances. This heat is retained for a longer time and soaks in the combustion chamber and other surrounding surfaces.
That means less heat in the pipe, and consequently slower wave speed, which is directly proportional to RPM. Also there is some effort lost in simply the piston's ability to compress a higher ratio. So you now have a different motor, which requires other calibration changes to many areas- clutching, jetting, timing and pipe design to name a few."