Quote:
Originally Posted by Davehuge
Sounds great... although surely reducing compression ratio = less power?
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Yeah nah yeah!
Increasing compression ratio increases power up to a certain point.. Too much compression can result in you having to run richer than ideal to stop pinging. Higher octane fuels can help as well.
High comp ratios tend to be quite snappy and responsive off idle. Taking some out lets the engine feel smoother... which is not always a bad thing in a dirt bike where we often struggle to put power to the ground.
I prefer to set my engines up with a tight squish (improved efficiency and power across the rev range), while keeping the compression ratio reasonable (to allow use of average fuels without worrying about pinging).
Lots of aftermarket tuners/head designs bump impression because it's an easy way for the end user to feel a change through seat of the pants.