93zder

I noticed my 93 Z feels as though it has less power when the weather is humid.

Could this be the opti acting up? When the humidity goes away it's fine.

slick1hunting

I will take an uneducated stab at this lol. Given its not a combo of things or a psychosomatic response lol. One thing I do know is water does help conduct electricity so perhaps the added moisture in the air is allowing current to be lost in some soon to be failing plug wires. I would suppose if its an electrical issue then using a spray bottle and moistening all aroung the engine might give you a light show or arcing( in the dark). Open up the hood on humid night and take a look as well as try the spray bottle. It might point to a problem. I am not sure if you would have any real noticeable effects on fueling with higher moisture content in the air since you are not at the track and knowing the consistancy or your car in the hundrenths of a second. So I really cant think of anything else so if it isnt an electricle issue I would assume its probably nothing.


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MDZ28

its funny I was just trying to explain this to my mechanic as well.

My car doesn't run as good when its hotter and when the humidity is terrible, but on low humidity and cool days it runs like a champ.

I have newer plugs and wires though so I'm not sure if that's the issue.

I was thinking opti as well but I wasn't sure. Im curious to see if anyone else has had these issues and what it could possibly be.

MyShibbyZ28

Are your plugs gapped correctly? Too wide of gaps can cause issues in hotter temps. Don't quote me but I think they should be 0.050".

Also, for what it's worth, I ran a 14.30 in the quarter in ~95*F, and 13.9 in ~60*F. Temperatures can affect the car a lot.

Injuneer

Humidity in the air entering the cylinders displaces oxygen, meaning less fuel can be burned. As temperature of the air increases, the density decreases, meaning there's less oxygen mass to burn, less fuel supplied and burned. Taken together they can have a significant effect on power output. Higher inlet air temps and hotter engines increase the chances of detonation, meaning you may be getting significant spark retard, particularly if you aren't using the correct octane fuel. High intake air temps (or increased heat soak of the IAT sensor) also appears to result in the removal of about 3* of ignition advance. That may explain the OP's loss of power.

However, it it not clear whether MDZ28 is experiencing a simple loss of power, or something else. What exactly do you mean by "doesn't run as good" - is this just a general loss of power, or does it result in misfires and rough running?

93zder

I was thinking heat soak as well. Im thinking LT1's are more prone to this as well? This would explain why on a cool night it runs so well and strong - cooler air = more oxygen to burn.

I do have a K&N CAI so maybe i can try to open up the bottom of the area where the filter sits in to allow more air to be available? Maybe some type of scoop too. Although if the air is crap them more of it might not help.

KW Baraka

All naturally asperated, internal combustion engines produce more power as air temperatures decrease.

Refer to 'Injuneer's' post immediately above your's.

And yes.....if the air is 'crap' (too warm/hot) more of it won't help because the warmer air will be less dense, and therefore.....less efficient.

KW

plattted

The Ingineer is right on. As humidity rises, oxygen levels decrease.

Just ask any long distance or track runner about the difference in their times when humidity increases. Same for engines.

93zder

I think i will run a datalog just to see if there is anything off. But i agree with you guys it's probably just the weather/oxygen thing.

Scrub88

It's just the name of the game . It's 98 degrees here 100% percent humidity
My car doesn't perform as well during the day ..if I take it out at night it's back to normal
Like stated motors love cold dense air .

MDZ28

by no means does the car run terribly when its hot and humid,merely just doesnt seem to want to get up and go like it does when its less humid.

I would say there's less overall power but its not a significant difference just noticeable.

PA94Z

From 60 to 90 degrees we could be talking 20 - 25 HP, which is definitely noticeable.

Injuneer

The change in air density (leaving out the grains of water) is inversely proportional to the change in absolute temperature. In the case of going from 60*F to 90*F the density is reduced by 5.46%. Your power will drop by that amount. With a 300HP engine, you're talking about a loss of 16.4HP.

There's is also the effect of barometric pressure, and changes in altitude. The best method to combine these factors is to calculate the "density altitude". Most tracks will post the density altitude for major events.

RamAir95TA

You can also see the DA for past days at the track at Drag Racing 1/4 Mile times - DragTimes.com. They have a section with a bunch of tools - check there.

KW Baraka

Yeah.......normal.

KW