I thought I would post up this fact as I have seen many posts stating the humidity was high thus they were down on power.
Higher humidity is a natural octane booster.
Higher humidity = air more saturated with water vapor. There are a lower number of oxygen molecules and there are a much larger number of water molecules interspersed between the oxygen and fuel molecules. The effect is that the space between the molecules increases, which slows combustion flame speed. As the flame front moves from fuel molecule to fule molecule the flame comes up against water molecules which slows the combustion process. Thus water suppresses violent combustion-detonation, just as a chemical octane booster does by chemical means.
This means that an increase in humidity will often compensate for increases in ambient air temps, which normally need a 1.0 octane increase for every 13deg C.
Conversely, a big decrease in humidity and increase in ambient temp is the worst case. (This is what I deal with out here in the AZ desert.)
That's why I'm looking into water injection to make up for the dry/hot conditions here.
Also Higher pressure requires higher octane, (or richer mixture or less timing advance).
This info was taken mostly from Forced Induction Performance Tuning by A. Graham Bell.
Happy Tuning

 

Well, I'll post up this fact. Everytime the humidity is high around where I live, knock count goes up, thus timing gets pulled, and power goes down.

His theory sounds good, but doesn't work for me.

 

The day you run a faster time in 95% humidity compared to 30% humidity at the same temperature you let us know. That is a BS theory. It may "raise" the octane but there is so much less oxygen to burn due to it being displaced by water that power levels drop. I have been racing cars for 9 years and my father and uncle for 30. Nothing is different today than 30 or even 9 years ago. Cars go slower with humidity. Basic. I see this almost every other weekend at the track. Humidity = bad not good.

 

nevermind

 

Well, as I don't get to find out about humidity out here; You guys that have experienced poor performance with higher humidities, were the temps also high. Humidity can only help so much. If its Hot and humid, the temps will be affecting the performance more.
If this is a BS theory, than how do you explain the performance gains with water injection?
With water injecting into the intake you'd be experiencing 100% humidity (plus) type conditions.

 

the difference is in the temp... not many places on earth do you find it cold AND humid.... it's usually dry and cold or hot and humid.....

 

humidity sucks.. it can get warm and very humid here.. Right now its 72f 100% humidity car will probably run like ***

I can't wait for this fall with 50f nights (no humidity)

 

haha! what a joke! some guy from ARIZONA saying humidity is a GOOD thing! why don't you come on over here to THE SWAMP in gainesville and convince me of that!

my ideal running conditions? a crisp fall morning, about 50-60 degrees. you WILL feel your engine pull harder then.

 

Actually, on a car with water injection and no other changes you loose around 10% power..... but with the water injection and pump gas you can increase boost pressure and/or advance the timing and this gives you a net gain in power over what you had at normal boost levels and no water injection.

Personally I am not willing to experiment with my car to see if you can run 28 psi of boost on 93 octane on a humid day without detonation

Keith

 

I think you guys are thinking too extreme.
Of course a morning at 50-60F you will feel the power, but I'm sure at that morning temp, the humidity is also up (notice dew on leaves).
By the way Florida boy, I'm from South FL. I know humidity, but you aren't going to get high humidities without the temps in FL.
I'm pretty sure most of the guys debunking this haven't done any kind of comparison.
We are in the monsoon season here, (which is not the monsoon you think of).
Last week was 103-105 with 40% humidity. This week it's 110-115F with 10-20% humidity.
My seat of the pants dyno says I'm down 20-40Hp from last week.

 

Just like anything else. If you install water injection you need to tune for it. Which means leaning the AFR out (12.5:1) and advancing timing. Increasing boost too.
If you guys talking crap read a little, you might learn something.
I've been forced into learning this due to my sit out here in the desert.
I'd love to be over in the land of 93-94 octane with humidities in the 30-40% and temps below 110F.

 

water vapor and humidity are two different things, high humidity = less power. cool moist air, like fog= high power.

 

I disagree. Either way you are introducing water vapor into the intake. Humidity is just more subtle.
The humidity will never be high enough to equal what water injection does for detonation.
High humidity is like water injection with a really small water injector.
I will be researching this further, as I have been. But everything I've read so far says. Moist air = less aggressive combustion. Which a friend to a turbo car.

 

cars seem to run very poor around here at the track in high humidity. theoretically, he could be right, but that theory is dead wrong at the tracks around here. (Lebanon Valley,NY , Atco,NJ , Englishtown,NJ.

 

But the only way to find out would be to run at same temperature and air pressure and different humitiy which is almost impossible to expect