Why is my car stronger when it's humid?

[Wolfen]

I noticed it runs better with alot more pull throughout the RPM range. Also any detonation like noises are completely gone. Just a solid rumble from the V8 and pulls hard in any gear. I noticed this effect when it's very humid outside and if it's been raining for a while. Why?

[Blauanzug]

Hmmm... a possible cracked intake? or a vacuum leak that is somehow stopped in the rain. BTW when has it last rained instead of snowed in NJ

[larinah]

Cooler air, the car is breathing better.

lol, pulled tht one out my butt but it sounds good tho.

[camoore]

my guess is air density.
opposite affect of losing power at altitude.

[Wolfen]

Originally Posted by Blauanzug

Hmmm... a possible cracked intake? or a vacuum leak that is somehow stopped in the rain. BTW when has it last rained instead of snowed in NJ

I have no vacuum leaks that i know of. lol. The car runs and idles just fine.

Also the temp has actually been higher here, 60 deg now as opposed to the 50's and 40's. So i dunno what gives. Maybe a water injection system can benefit after all?


BTW: It rained all last night.

Originally Posted by camoore

my guess is air density.
opposite affect of losing power at altitude.

You mean the air is denser when it rains? If not, could it be the steam effect of the water coming out of the air under combustion?

[mattmartindrift]

dyno proof or it's just speculation, you know, placebo effect.

[colombobeat]

water vapor reduces the intake air temp (due to high specific heat) which in turn makes the air even more dense. It also further reduces the intake temp if the water vaporizes (due to high latent heat) and also tries to increase in volume. When water vaporizes in the chamber (Since volume is finite), this means a small amount of added pressure.

I am sure you guys have heard of water injection for turbo intakes back in the 60's. I have heard of many European, African and Asian turbo diesel trucks being setup with homemade water injectors. This was also beneficial in reducing hot spots inside comb. chamber and cleaning up some of the deposits.

i am not sure the exact optimal ratio and even if the added power is actually measurable. You do feel it on the butt-dyno though..

[camoore]

www.google.com




In regards to intake of moisture into your car's engine, the advantage is two-fold: firstly, humidity can tend to go hand-in-hand with cooler ambient temperatures. Yes, I know it's not always the case (Florida, North Carolina, Thailand), but more often than not, air tends to get cooler with the presence of moisture. And we all know that cooler ambient temperature increases engine performance.

HOWEVER, the most applicable advantage to adding a bit of moisture is thermodynamically. As the water is injected into the hot intake stream, it wants to vaporize and expand. Fortunately, when liquids vaporize, or compressed gases expand, they take in a lot of heat. This intake of heat is manifested by a removal of heat from the surroundings -- thus the air feels cooler. Likewise, when you compress something, huge amounts of heat are given off -- which is why your turbo gets so damn hot.

This vaporization of the water lowers your intake temperature. And, as we've discussed, lower intake temperature = better performance.



at 70F
30% RH air density ~ 0.075 lb/ft^3
80% RH air density ~ 0.073 lb/ft^3
a 1.5% difference, not much, but it adds up

at constant RH of 50%
40F density ~ 0.079 lb/ft^3
90F density ~ 0.070 lb/ft^3
an 11% difference

so both temp and humid have an effect, but temp's is greater

at 40F/30% RH density 0.080 lb/ft^3
at 90F/80% RH density 0.069 lb/ft^3
a 15% difference almost directly proportional to HP gain (loss)

[mattmartindrift]

if you don't advance timing to take advantage of the cooler temps, it does very little.

[camoore]

When i put my 540iA in "sport mode", does it advance the timing? It sure feels like it sometimes.

[mattmartindrift]

Originally Posted by camoore

When i put my 540iA in "sport mode", does it advance the timing? It sure feels like it sometimes.

I assume you mean by turning off DSC?

it gets rid of the fly-by-wire throttle lag and might change the trans program on automatic cars.

[02540ico]

Sport mode just ensures your car starts off in 1st gear, and holds the gears longer. Normally it'll start off in 2nd, or shift to 2nd immediately, so it feels like less power.

[blackxs]

Originally Posted by Wolfen

Also the temp has actually been higher here, 60 deg now as opposed to the 50's and 40's. So i dunno what gives. Maybe a water injection system can benefit after all?

You mean the air is denser when it rains? If not, could it be the steam effect of the water coming out of the air under combustion?

Originally Posted by mattmartindrift

if you don't advance timing to take advantage of the cooler temps, it does very little.

Originally Posted by Wolfen

I noticed it runs better with alot more pull throughout the RPM range. Also any detonation like noises are completely gone. Just a solid rumble from the V8 and pulls hard in any gear. I noticed this effect when it's very humid outside and if it's been raining for a while. Why?

I have a feeling the fuel you are using or something is causing pre-detonation under normal conditions, causing a slight loss in power. Your car detects this and alters timing accordingly BUT when it rains, the water (a la water injection) prevents knock by having a higher specific heat and its other properties, thus allowing the engine to push timing to where it should be, where its making the most power, and so you feel this as an appreciable power difference raining vs. non raining. Any benefit due to air density would be outweighed by what you say is a 10-20 degree difference from the days you are comparing it to. Some places dont cool down with moisture in the air, with this knowledge coupled with your statement of detonation noises dissapearing leads me to believe that your problem is pre-detonation and in this case moisture in the air is your solution.

BTW water injection was in lots of production model GM engines prior to the 90s. It was a great system that allowed higher compression ratios and thus more power off less sophisticated engine degins. Problem is people werent refilling their systems, so a lot of the water injection engines have bit the dust. If I can find one I want to buy it, think it would be a fun little ride

[mattmartindrift]

yeah, there should be NO detonation when using recommended fuel or fuel of a higher octane rating - something is wrong.

[PatrickW]

Is there much use of water/meth systems on NA cars? I want to get an AEM kit for my volvo along with a bigger turbo but NA applications dont have near as much heat going on as far as the air temp at the throttle body is concerned..

[weasel like]

First interesting thread I've seen in a while! Good question OP.

I've actually had a dissimilar experience with humidity in VA on really hot days. My motor feels like its struggling more compared to cooler evenings when the air is chilly. I guess that is more due to the air temperature than the humidity though... Interesting nonetheless!