Humidity should make quite a difference. The combustion of fuel in the "chamber" is a mix of a given amount of fuel and the oxygen available in a given volume of air. I would think humidity plays a larger role than temperature (although the two are related). If there is more water (higher humidity), then the percentage of available oxygen (when compared to the same volume of "DRY" air) is less. Therefore, you have less "combustion" potential" per cycle and the perceived (although real) drop in power (efficiency) during hotter temperatures/higher humidity, etc.

 

Didn't notice it until I went for a night shopping trip yesterday while it was 46 degrees outside. Wow, the motor was climing revs like it ain't no thang. Almost like something was disconnected and reduced the friction.... it just kept going higher and higher without the stickiness.

 

Here are some tests I did to check hot engine vs warm engine acceleration.
Was not able to fully test intake temp effect but you can see a small effect from only a few degrees c .


https://www.rx8club.com/series-i-aftermarket-performance-modifications-23/cool-vs-hot-acceleration-test-results-101595/

 

Thanks for the explanation mabdeliz.

I'm still trying to figure out if there is something wrong with my car or if it is just the temp/humidity that makes such a huge difference. From the way it drives, I'm guessing the difference in HP between a 70 degree dry day and an 90 degree humid day is probably 20HP or more. Is this to be expected? Is the rotary more susceptible to temp/humidity because of the high output from such a small displacement (1.3ltr) engine?

I brought in to the dealer 3 times already and was told all 3 times that the car is within specs, so there's nothing wrong with it. I'm frustrated.

Oh, and before anyone brings it up... I'm comparing with the AC off at both temps.

Anyone else notice such a dramatic difference?