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I’m new to honda and the k engines but i’ve been looking to pick up an 8th or 9th gen civic but wanted to know which was better for making power? And my second question is do all trim levels of the civic use the k20/24 for the 8th and 9th gen?

 
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8th gen for sure if you want to make more power. It came with a K20 and the 9th gen came with a K24. That specific K24 has a pretty poor aftermarket in comparison (pretty much the same engine as what’s in my TSX).

As for trim, if you want a K, it has to be the Si. Other trims came with the R engine.

 
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The K24 in the 9th gen Si isn't a terrible engine by any means but I would have to agree. The K24 head has a single large exhaust port unlike the K20 where each cylinder has it's own. A popular mod to the 9th gen K24 is actually to swap the head with an older K20/K24 head.

You can still make good power on the 9th gen though. Throw a supercharger on it and you can get ~350 whp from a "stock" engine.