More power in hot weather?

[65CrewCabPW]

I'm seriously confused about this... Why does my slant six actually have MORE power when it's 90 degrees and the motor's working hard (above it's normal temperature, but not overheated)?

I have a hill outside of town that during the winter I have to climb in 3rd gear... but since it was just about 90 today the truck got to 58 in third, and proceeded to pull the rest of the hill at 55 in high gear... something it just won't even dream of doing in colder weather.

I would think that with a cold air intake and dense air, and breathing in cold, dense air, it would outperform what it does when it's hot weather. But it's significantly weaker (and I notice, because it's a slant six, hauling around a 5400 lb 4x4) when it's 35 or 45 degrees outside. Any ideas?

[BigBlockMopar]

Do you have any kind of mixture-measuring device in the car to check if the engine runs rich or lean under power?
I would think your engine could be running rich or lean most of the time, to the point it looses some power. Now with hotter temps the mixture is probably 'better' and lets the engine make more power.

Also, most folks underestimate the 'power-freeing' effects of a thinner (motor)oil.

[Steptoe]

I tend to go with the explanation above.
Struck something very similar years ago, thu not as dramatic.
If your 'normal' mixtures and timing are borderline, a change in air temp (density) will change the speed of the flame across the chamber, which means the timing is out for that mixture at a given load and rpms.
Generally such a situation is not helped by having the timing curve at that load and rpms slightly to far retarded..
There is a point when retarding within only a couple degrees where power/ economy drops off quite dramatically. If u are just on or just below this piont the change in air density, be it temps or altitude will effect as described.
A quick fix would be up the initial a couple degrees, a better would be speed up the curve (lighten up one of the cent springs) a little if the rpms this happens at are still below the total advance (initial+cent) and VA is not being activated...ie engine vaccuum below that of the initial activation of the VA canister.

As suggested above I would also be checking that u do have a rich enough mixture under this load and rpms.

[storm]

Don't discout the effect of thicker lubricants in the drivetrain either. I remember when I lived in Darwin Australia (tropical climate) and had a friend in Tasmania (cold climate) the same types of cars would get different oils in the engine and drivetrain because of the climate difference. I am considering putting an automatic in my 4wd because the g/box is pain to change gear in, especially 2nd to 3rd, in winter yet in summer there is no problem at all. All these things cause horsepower "loss" or at least the feelng of it.

[65CrewCabPW]

Ok, well, operating under the theory that cold, dense air, burns a little faster than hot, thin air, I tweaked the timing curve a little.

In my case, the slope got a little more gentle but went farther.

I added a degree to the the top, dropped the middle a little farther, where it has trouble pulling the hills.

And, tweaked the mixture valve slightly leaner. The result was that I actually got quite a bit more horsepower. And, since if I can ever work it out, I'm putting in a dual exhaust, I'm not even working on a mixture monitor right now. However, I do know mostly whether it's rich or lean. And it's not lean, nor significantly rich, either.