29 degrees F in Texas--near sea level elevation
 

Was driving around a bit tonite after seeing friends. In austin, it's what like a few hundred feet above sea level. And temps were under 30 degrees F. Man the engine LOVED the cool dense air. Honestly felt like the car had about 220hp (it's all stock except for k&n filter). Yee haw!!

More power and less grippy tires, if you know what you're doing you can go have some slide-happy fun. But be careful.

100 feet elevation difference is negligible on the performance scale, motors only really start to taper off once you hit the 2000-3000 ft. range, same thing with air temp, you've got to be comparing around 50 degrees difference to have measurable performance gains, and it's negated since the air is piped through an engine bay that is probably anywhere from 100 to 150 degrees, since it isn't magically fifty degrees warmer in Austin over the past few weeks I doubt that had much of an affect either.

It was probably just the thrill of the drive in a new stomping ground without a care in the world, that magic feeling only nighttime brings. Still a special moment.
:cheers:
:burnrubber:





I catch myself sometimes understanding why a lot of people hate the technically minded...

Yes it is. It was 75 here just 2 days ago. Now it's 25. Big difference.

Also.. OP wasn't saying the difference between 100 and 0 sea level. His point is down here, we are at a very low elevation but still get the low temps occasionally. That way, the air is more dense here than somewhere you get 25 degrees regularly.

I.E. denver gets 25 degree weather regularly, at 1600m. we get 25 degree weather at 30m. like you said, you'll see a difference

That's about -1,500 feet density altitude. Think your car performs good, you should see how big of a difference it makes in an airplane :thumbsup:

Glad to hear Im not the only one that noticed!!
:thumbup:

I noticed it last year in my Nismo 370Z when I was living in Houston. There was a couple days when it dropped under 30 and the car was a bit more enjoyable.

Lol yes, this is exactly my point! I had my FRS in colorado about a month ago actually, def noticed the difference UP there. Gotta love low elevation.

:thumbup: ....... I think the middle part of your post had it "righter" ........ but hey, technical minded is OK .....:)

humfrz

Yes, yes it is. I can't find a reliable article so I'll break out the textbooks when I get home and figure out how much fifty degrees affects horsepower.

:cheers:

Floridian here, woke up this morning in the sub 30's as well. The car started idling at like 2k trying to warm itself haha.

I'm actually really interested in this. Let me know what textbooks you got :cheers:

I used this one:
[ame="http://www.amazon.com/Engineering-Fundamentals-Internal-Combustion-Engine/dp/0131405705/ref=sr_1_1?s=books&ie=UTF8&qid=1388782265&sr=1-1&keywords=internal+combustion+engine+engineering+ fundamentals+pulkrabek"]Engineering Fundamentals of the Internal Combustion Engine (2nd Edition): Willard W. Pulkrabek: 9780131405707: Amazon.com: Books[/ame]

So basically went along the route of finding the difference in density between 25 degrees and 75 degrees, made a ton of assumptions and shortcuts: mainly that the engine operates identically at both temperatures (losses and fluid flow effects), whatever heat added to the intake charge from ambient temperature has linear effect on density (definitely not true), and whatever else I'm forgetting. I also looked up a bunch of stuff that I didn't need to illustrate this.

Basically for every kilogram of air in the chamber there's X kgs of fuel which is combusted for energy which the pistons turn to work, since all we're doing is varying the temperature and consequently the density all you really need to do is calculate the two densities and find the ratio between them to get the theoretical power gains by operating in a cooler environment.

So, using this formula from my textbook:
http://i.imgur.com/YYQ05r8.jpg
(keeping 101 kPa because I'm lazy)

I calculated the density of 25 degree air to be: 1.307 kg/m^3
&
75 degree air to be: 1.185 kg/m^3

You can go ahead and figure out the volume of air sucked in, throttling losses, volumetric efficiency losses, air fuel ratios, heating values and such but really you're just multiplying the two numbers above by relatively similar values, the ratio of energy created in the chamber will be roughly the same before and after those calculations, which by my hand is about 10.4% for the temperatures I chose.

Wow, 10.4% power gain over a week, I admit I am surprised, I didn't expect it to be so high. Maybe the OP really was seeing a +20hp gain at the crank, my apologies for assuming it was the error of the butt dyno.

I must state that the 10% number I came up with is fake, it's the theoretical maximum you could gain from going -50 degrees on ambient temperature. The truth is the formula isn't linear, 25 vs. 75 is different from 75 to 125 (9.4% BTW) and the ambient air temperature passes through an environment that heats it up and expands the charge. So realistically you aren't seeing ambient temperatures at the chamber and the delta between the two environments won't be as large, warm air coming through a hot environment heats up a little, cold air going through a hot environment will heat up more. This reduces the gains you would expect based on my calculations.

So let's ballpark it, 25 degrees vs 75 degrees. We know the coolant temp runs hot, right around 180 degrees so lets assume the engine bay environment is 150 degrees. So lets guess that the 75 degree ambient air gets heated up by 25 degrees running through restrictive tubing that is heated up by the engine, 100 degrees as it fills the combustion chamber (which also heats up the air as it runs through the head past the valves). Eh, the number isn't real but the idea is.

Same engine operating at the same temperature (roughly speaking), you've got pretty much the same amount of heat being generated (within 10% right?) and a similar environment to cool it off. But since the 25 degree air is cooler it's more accepting of the heat from the engine bay, it's going to increase by more than 25 degrees, let's say it increases by 5 more on top of that, 55 degrees, all of a sudden our gains go from 10.4% to 8.7%, again these numbers aren't real but the principle is. You will never see that 10.4% gain in real life if all you're controlling is ambient temperature.

Feel free to build a spreadsheet based off the above equation and play with the numbers, maybe you'll agree with me when I'm skeptical of 'cold air intakes' when at best they're decreasing your inlet temperature by a couple of degrees while adding extra length of piping that will heat up the air as it passes through.

I'm sure my rambling is full of holes to be filled and attacked, I await contribution.
:cheers:

Have I mentioned how much I love being from TEXAS?