Does weather does affect performance?

I honestly think humidity plays a big factor and it's rarely talked about. For example, you mentioned that your car drives great during 90 degree days in California. Here in sweaty, humid Maryland, we often see 90 degree summer days with 90% humidity. My car feels like a slug in those conditions.

Here's an explanation I found online from a discussion at another car forum:

"Humidity and heat, both. When the air is cold and dry, your car will definitely feel faster than ever. The hotter the air is, the less dense it is. And when the humidity is high, more air is being displaced by water molecules. So heat and humidity together are a double-whammy."

ablueSI said:

Oh I have, twice now I was indeed amazed! The car felt incredible.

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Well there you go. No explanation needed

gtman said:

I honestly think humidity plays a big factor and it's rarely talked about. For example, you mentioned that your car drives great during 90 degree days in California. Here in sweaty, humid Maryland, we often see 90 degree summer days with 90% humidity. My car feels like a slug in those conditions.

Here's an explanation I found online from a discussion at another car forum:

"Humidity and heat, both. When the air is cold and dry, your car will definitely feel faster than ever. The hotter the air is, the less dense it is. And when the humidity is high, more air is being displaced by water molecules. So heat and humidity together are a double-whammy."

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That makes sense. In Northern Cal we don't have nearly the humidity as the East Coast, Texas, etc. It could be 100 F in the day, and in the evening you might need a jacket! Southern Cal is a bit more humid, so it makes sense that when I hit LA traffic after a long drive in a lot of heat the car heat soaked

I have noticed the opposite. The colder the temp, the more power and better throttle response I feel. Now, here in Charlotte we don’t get as cold as some of you, but it was not only noticeable, it was obvious. Teaching my 15 year old to drive in it and even she noticed. MPG was down quite a bit though and these all seasons suck ass in the cold weather.

On the other hand, hate the hot summer days. Always noticed the decrease in performance on all my cars but not to the extent of this one. It’s my first turbo car so I assume turbos are more affected by the hot weather.

amirza786 said:

I've owned my 2018 Civic Si Since June (8 months), and I notice that temperature does affect performance. I have found that if the temperature is 50 F and above, my car performs much better, everything from acceleration to better gas mileage. For example, yesterday was a nice 55 degrees F, and everything was so much smoother, from shifting to basic acceleration. Also I was averaging 31 mpg doing some spirited driving. This morning the temp was 38F (cold for the Bay Area), and even after everything was warmed up, I felt as though I had to push down harder on the pedal. Accelerating seems a bit more restrained, shifting not as smooth, and average gas mileage this morning dropped to 26 mpg. Also I feel boost takes a bit longer and is much less.

What I feel is that this car drives much better between 50 degrees and 90 degrees F. I don't know if it's the ECU maybe tuning things down or possibly the transmission doesn't work as well in the cold. I don't have this issue at all with my two Toyotas, they drive the same cold or hot weather. Does anyone else feel the same, that your Si drives better in warmer weather? I would like to know if I'm the only one who notices this.....

EDIT

I want to make it clear, it does not drive bad in colder temps, performance just seems a bit down compared to driving in warmer temps

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Are you in an area that only gets 91 octane? It may be the car has to adjust timing to prevent knock due to the more dense oxygen rich air. On east coast on 93 octane I feel the car is more responsive in cold weather. Maybe try a tank with some octane booster and see if it has any impact.

fabrizzio71 said:

Are you in an area that only gets 91 octane? It may be the car has to adjust timing to prevent knock due to the more dense oxygen rich air. On east coast on 93 octane I feel the car is more responsive in cold weather. Maybe try a tank with some octane booster and see if it has any impact.

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California only has up to 91 octane, that is unless you own a plane and take your car to the airstrip!

almost every car ive owned had better response/acceleration in varying degrees in cooler temps.

super hot weather is the worst for performance. like 80 degrees and warmer.

amirza786 said:

California only has up to 91 octane, that is unless you own a plane and take your car to the airstrip!

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Oh wow I did not know that and that blows... I guess I assumed 93 was available everywhere in the US

Horsepower/torque is a direct function of air mass.

For any given volume of air, the colder it is, the more oxygen it has in it, this is density. If there is water in that air [humidity] the air is less dense because water molecules take up more space in the volume than the oxygen molecules.

The whole function of a turbo is to increase density which in turn increases power.

As an example, for 1 cubic foot of air at standard atmospheric pressure [~14.7 psi @ sea level] there is a unit of mass of oxygen. If you double the pressure in that cubic foot [29.4 psia or 14.7 psi], there is double the air mass in that cubic foot of air [in theory]. This is what a turbo does, this is what turbo psi means.

There are some caveats to this.

If the air isn't just oxygen and nitrogen, for argument's sake let say you add water vapor [humidity], the density changes because the molecules of different compounds take up different volumes.

If the air is hot, the oxygen is more sparse, the molecules are farther apart, so there is less oxygen mass in the air. If the air is cold, the oxygen in it is more dense, so you have more oxygen.

An engine can only burn fuel if there is oxygen to mix with, the more oxygen, the more burn, more burn, more power.

Yes, your engine feels more powerful with colder intake air ...

Because it is.

Unless the computer controlling the burn adjusts for it.

I can continue to explain why you loose power as temperature rises, but I think you get the idea.

If you really want to understand this learn the ideal gas law inside and out.

Otherwise, please accept my simplified explanation.

Davsonamission said:

Wait what? Really? It is a turbo car the colder the better or am I getting that completely wrong? My car is noticeably faster in colder weather... I think

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I agree, it feels quicker in cold weather, but traction sucks on cold tires / pavement and it kinda ruins the fun for me... My tires tend to skip under hard acceleration in cold weather. I hate that.

Davsonamission said:

Oh wow I did not know that and that blows... I guess I assumed 93 was available everywhere in the US

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Here in OK 91 is generally the highest you can get. In OKC we have like three stations that sell 93, and it's way more expensive. I just mix ~2 gallons of E85 with a tank of 91 to get 93ish, though. Ends up being cheaper than even just filling with 91, since E85 is generally cheap.

odinist said:

Here in OK 91 is generally the highest you can get. In OKC we have like three stations that sell 93, and it's way more expensive. I just mix ~2 gallons of E85 with a tank of 91 to get 93ish, though. Ends up being cheaper than even just filling with 91, since E85 is generally cheap.

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Huh interesting... its cool how gas can be so different in certain states. Like some states do not allow you to pump your own gas and now I find out that the octane I take for granite because it is at every station here is not available or hard to find in certain states.

Winter and Summer gas blends also have an effect on the performance too.

Summer blend has close to 2% more energy than winter blend.

On winter MPGs should be normally worse due to the combination of different factors like the gas blend and weather.
Colder Air requires more fuel to keep the air fuel ratio on check. Remember that cold air has generally more oxygen so if the ecu don't add more fuel the car will run leaner than normal. To overcome this the ECU adds more fuel to the mix.

Davsonamission said:

Oh wow I did not know that and that blows... I guess I assumed 93 was available everywhere in the US

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Actually I was wrong, you can get up to 100 octane, but there are only a few gas stations around California that offer it, and it's like $8 a gallon. Premium used to be 92 octane standard, but California banned the additive MTBE (which is a carcinogen that was showing up in groundwater) which was primarily used as an additive to oxygenate gasoline, so refiners switched to 91. Really, I don't think there is to much difference using 91 or 93, you probably have a very minor performance bump