Looking at a boat with twin 300sx that runs 95mph at elevation of 800'. Any idea what it would run at 1700'? Does elevation effect the 300sx much? I know with the 525's same scenario I ran about 3-5 mph slower.

elevation will effect the performance of every engine,even if it has the best fuel injection and self tunes.less air requires less fuel and that means less power.

800ft = 7.2hp loss per motor

1700ft = 15.3hp loss per motor

When comparing an engine that makes 300hp at sea level.

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Plugging in a 525hp engine:

12.6hp loss per motor at 800ft

26.78hp loss per motor at 1700ft

Note: most 525's dyno closer to 560hp. Therefore, it will lose a little more hp than I stated above.

My boat at 1500 feet is about 2-3 mph slower than sea level. I didn't think it would be that much but it is. I think 1 of those mph could be gained back by a jet change/slight carb tune but not worth it for a long weekend.