Humid weather effect on performance
 

Yesterday morning on a clear, quiet drive to work I noticed something spectacular about how my fr-s was feeling. Everything about the engine and throttle response was crisp, accurate, and buttery smooth. As my drive went on I put more and more focus on the rpms and just how quickly the needle punched through each mark on the tachometer.

It was a little after 6 am when I hit the road and the air was so clean, cool and completely still. I live on the coastal region in Virginia and generally we have a pretty fair amount of humidity... on a hot mid-summer morning you can seemingly break a sweat before the sun even peeks. Being so caught off guard by the increase in performance on the pants dyno, I reminded myself to compare the ride home around 4pm with plenty of hot air and a more humid atmosphere. Sure enough things started to bog down a bit. The throttle response was not as sharp and there were definitely moments where the revs seemed to choke(not talking about torque dip). It just felt like the 86 had run a 5k and was gasping for air, compared to in the morning where it was free to be out of its own way.

In an attempt to conclude the weather as the factor, I did check the temps on the google weather app, and oddly the humidity reported contrarily at 89% humidity and 64 degrees in the morning; and only 76% humidity and 71 degrees during the ride home, even though there was a brief shower and noticeable moisture slightly before that drive. But I have no how accurate or real-time the data is for the app.

So have any members experienced this same behavior in humid climates? And are there any tricks or minor mods to help circumvent the engines response to hot air and make it more adaptive?

Temps make a BIG difference. Humidity does too but not as much. I notice this all the time

With that small of change in humidity and temperature ........ I think your pants dyno is ah messen wich ya .........;)


humfrz

you can certainly tell difference between the dog shit hot texas summer days and a cool winter day on how the car breathes. but i cant perceive more humid to not, 400 miles from coast doesnt get quite as balmy.

Go away, you live in Calgary...It's a desert. Do you know what humidity feels like? lol

My Fr-s doesn't like hot humid days and refuses to play. ;)

LOL to be honest... no hhahahahaah!

Well, picture what you feel like after you get out of the shower (Wet)

Sexy?? :iono:

haha!! :clap:

I definitely feel a difference in varying conditions of temperature or humidity.

I live in the SF Bay Area south of San Francisco. What I've noticed is that warm, mild humidty is the best condition for the car. Warm meaning 75 degrees. I've never driven the car in super hot weather (90 degrees +) but I've driven it in cold mornings around 40 degrees and it felt like crap.

I did drive it one night with a moderate humidity with the temperature around 65 degrees and it was beautiful.

Spend a week in Asia during the mid summer and you will know what real humidity is.

So the consensus is that hot air (and not specifically humidity) is harder on the engine? What exactly causes the engine to choke on hotter temps? I've heard of track days getting ugly if the engine goes over temp but what is going on that makes this the case?

Oh, I reckon that on hotter days, an engine runs a tad bit hotter and the air contains less oxygen.


humfrz

Also, the ecu doesnt like high iats. In south fl the car feels respectable in early am and relative dog shit in the afternoon.

Relative humidity depends on the temp as much as the amount of water in the air. Check on the weather site for Dew Point instead- that is the absolute amount of water in the air independent of temp.

64° at 89% RH = 61° DP

71° at 76% RH = 63° DP

I don't think your car will notice a diff in 2° of dew point, nor will you. The diff between 64 and 71... I'd say that was all butt-dynoitis and there was not real difference. Were you in a lot of traffic on the ride home? If you were in some stop n go traffic and your intake got heat soaked, that'd cause some issues.

That's not a real high dew point and is pretty much a perfect temp for the ride home. Your car will like that a lot better than 90°+ and a 70°+ dew point like in the summer though. That's the nasty muggy weather.

"The horsepower and torque available from a normally aspirated internal combustion engine are dependent upon the density of the air... higher density means more oxygen molecules and more power... lower density means less oxygen and less power."


...and for those of you who slept through high school physics, cold dry air is more dense ("oxygen-rich") than warm moist air.
https://wahiduddin.net/calc/cf.htm

Performance is markedly better when not in the middle of 100+ degree South Carolina summers. It helps not having to run the A/C 100% or the time as well.

Yea I considered the traffic going home to be not at all a fair comparison, I could have been feeling something that wasn't there, but it's still hard to dismiss..
Thanks for breaking it down.

Its mainly the temperature difference that seems to help...been very nice the past few weeks with the cooler weather, summer finally seems to be on its way out. Humidity is usually highest at the lower temperatures though, if you look at Temperature/Humidity charts you will see the 'phase shift' going on where humidity drops as the temperature increases throughout the day and rise during the night, peaking just before sunrise.

Very Hot temperatures + humidity feels much worse on your body than cooler temperature + higher humidity levels though. Going from highs in the high 90's to low in high 60's that first time had a very noticeable effect on the car.... It's almost nice enough to not have to run the A/C now, but still not quite yet...

Things I have noticed the FR-S loves:

- Cool Autumn weather
- 40% fuel level (optimal handling)
- Lightweight wheels and tires, and with the tires being slightly smaller in diameter

Humidity does affect it but not as much as temp if I recall correctly. Probably placebo

Yep, technically, the amount of oxygen in air is reduced, when the humidity is increased.

But, like you said ..... it may not be significant.


humfrz

Not just the amount but the compressibility of the air in general. More due to the heat than the humidity though. That is one reason why turbos get intercoolers.


I saved us $120K a year just by bringing cooler outside air into the plant compressors at work (they used to just draw the air from around them). We see about a 10% to 15% decrease in their efficiency during the hot humid days in summer. Now, of course these are compressing way more air than any car does but the principle remains the same.