Cold Weather=More power. Why?

[Deep Six]

I assume then that the MB 6.2l does not have the knock sensor that you refer to because this car could run low 11's in the Florida winter (this day was in the 40's) but high 11's during the summer. Dozens and dozens of runs maintained the same result: 50 degree drop in temperature cut half a second and added ~4-5 mph trap speed.

[ame="http://www.youtube.com/watch?v=HRyHsrutIvI"]DadsC63 runs 11.449 @ 123.64 - YouTube[/ame]

Research negative DA for more information

[Suberman]

A little quick google on the pseudo internet gives a rough adjustment of 1% per 10 degrees of intake air temperature delta. I assume that's F but it might be C because the official correction is adjusted by Kelvin. Kelvin degrees are the same size as Celsius degrees. That is without any knock sensor effects. Research continues.

As for the drag strip runs referred to you will also need to adjust for tire and road surface temperature effects.

[humfrz]

Originally Posted by Suberman

Ah yes, the notoriously accurate butt dyno.

It's probably just the lower rolling resistance of those summer tires in the cold.....

If there is an effect from ambient temperature then the effect should be even more noticeable with higher elevation and lower air temperature. A simple winter v summer acceleration test in Denver should establish the power gain. If the same test in San Francisco produces no acceleration advantage in cold weather then the question will be answered.

Or somebody could ask a dyno operator what they do about adjusting for ambient sir temperature and barometric pressure when they calculate your ( probably phantom) whp gains from your CAI.

There's nothing pseudo about the Internet.

Oh, my ..... OK, how many fell off the pumpkin wagon here ... ??

humfrz

[humfrz]

Originally Posted by Suberman

A little quick google on the pseudo internet gives a rough adjustment of 1% per 10 degrees of intake air temperature delta. I assume that's F but it might be C because the official correction is adjusted by Kelvin. Kelvin degrees are the same size as Celsius degrees. That is without any knock sensor effects. Research continues.

As for the drag strip runs referred to you will also need to adjust for tire and road surface temperature effects.

hmmmm.......??

http://www.diffen.com/difference/Celsius_vs_Kelvin

humfrz

[Synack]

Cold weather is doing my turbo well. I was able to lose traction in a straight line at the top of 3rd gear (~70mph) yesterday. Completely dry streets. I was surprised and super excited at the same time.

[strat61caster]

Originally Posted by Synack

Cold weather is doing my turbo well. I was able to lose traction in a straight line at the top of 3rd gear (~70mph) yesterday. Completely dry streets. I was surprised and super excited at the same time.

I would argue that has more to do with cold tires being less grippy than cold air actually giving your car a bump in hp. Not to mention worn tires since you've been playing with the turbo enough to know when this set loses traction meaning you've attempted to break traction in third gear before.

[chrisl]

Originally Posted by humfrz

hmmmm.......??

http://www.diffen.com/difference/Celsius_vs_Kelvin

humfrz

The statement was correct - Celsius degrees are the same size as Kelvins. The two scales only differ by an offset of 273.15.

[Synack]

Originally Posted by strat61caster

I would argue that has more to do with cold tires being less grippy than cold air actually giving your car a bump in hp. Not to mention worn tires since you've been playing with the turbo enough to know when this set loses traction meaning you've attempted to break traction in third gear before.

I admire your knowledge of auto stuff, but I had already been driving for a while on warm tires with 90% tread.

[chrisl]

Originally Posted by Suberman

As for the drag strip runs referred to you will also need to adjust for tire and road surface temperature effects.

True. Since the tires have less grip at cold, the fact that the car was still putting down faster runs despite lower grip is a strong argument that it was making even more power than you might guess from the times alone.

[strat61caster]

Originally Posted by Synack

I admire your knowledge of auto stuff, but I had already been driving for a while on warm tires with 90% tread.

Apologies, lots of people like to post about how awesome some event was (I remember one story on here about an AWD vehicle getting stuck in the snow while a FWD drove on by, there's also an exploding ricer thread in off-topic right now) when objectively speaking there's a simple less impressive explanation.

Your post gets my approval (I won't bring up road conditions which I'm sure you keep consistent in your butt dyno tests)

[Synack]

Originally Posted by strat61caster

Apologies, lots of people like to post about how awesome some event was (I remember one story on here about an AWD vehicle getting stuck in the snow while a FWD drove on by, there's also an exploding ricer thread in off-topic right now) when objectively speaking there's a simple less impressive explanation.

Your post gets my approval (I won't bring up road conditions which I'm sure you keep consistent in your butt dyno tests)

Haha, I hear ya man. Once the weather gets cold and frightful, all the new threads start popping up with 'my car did this' and 'my buddies car did that'. I had a guy one time tell me that his Acura RSX non-type-S gained 25whp from the colder weather.

[Wepeel]

Unless I missed it, I haven't yet seen any mention of timing compensations based on IAT. I haven't yet looked at the compensation tables for a BRZ, but I know on other platforms there are timing compensations for all sorts of things... water temp, IAT, load, etc. What I remember from the IAT compensations was that timing was most advanced (optimized) in "safe" IAT ranges, something like 30-70 degrees. If it's too hot, timing will be pulled, and if it's too cold, timing will be pulled. This is in addition to whatever timing may be pulled due to perceived knock events. Anything above or below that, timing started being pulled. So in addition to air density that would have something to do with it.

It would be great if someone who's seen the tables can confirm (or deny).

[ZDan]

Of course colder denser intake air *does* give more power, this has been fully established experimentally. The additional air shouldn't cause the engine management to pull timing. More air = more is squished, but it's *colder* to begin with, in colder temps the compressed charge should still be colder vs. in warmer ambient temps. Should be less likely to have timing pulled, I would think.

SAE J1349 Revised AUG2004 (Tc = ambient temperature in Celsius, Pd = ambient pressure in millibars)

http://wahiduddin.net/calc/cf.htm

Running the numbers, this shows a 10C/18F change in temperature => 2% change in power.

To my mind, the only question is how effective aftermarket CAIs are vs. OEM. My guess is: little to no improvement.

[Suberman]

Originally Posted by ZDan

Of course colder denser intake air *does* give more power, this has been fully established experimentally. The additional air shouldn't cause the engine management to pull timing. More air = more is squished, but it's *colder* to begin with, in colder temps the compressed charge should still be colder vs. in warmer ambient temps. Should be less likely to have timing pulled, I would think.

SAE J1349 Revised AUG2004 (Tc = ambient temperature in Celsius, Pd = ambient pressure in millibars)

http://wahiduddin.net/calc/cf.htm

Running the numbers, this shows a 10C/18F change in temperature => 2% change in power.

To my mind, the only question is how effective aftermarket CAIs are vs. OEM. My guess is: little to no improvement.

Yes, 1% for every 10F. This is the SAE correction factor based on an assumed ambient air temperature of 25C. (298K).

So even at 0C the theoretical increase in peak power at 7,000 + / - would be 5% or 10 hp. Peak torque would increase to 158 lb ft.

But when it gets properly cold, say minus 30 C, you should theoretically get increases of peak power and torque in the order of 11% or 22 hp....

I don't think so and I've certainly not experienced it.

While one might use peak torque on a daily basis peak power is hardly ever accessed in normal driving.

Elevation effects are more noticeable because engines are tuned to barometric at sea level which is around 1,000 mb. Not sure why SAE corrects to 990 mb.

Air with less density than at sea level cannot be compensated for. Air that is cooler than 25C can. If ambient is higher than 25C then the engine will lose power from the SAE rated power. A knock sensor can only limit excess cylinder pressure.

The drag strip results for the Mercedes 6.2l are interesting because we know AMG tunes those engines to very high specific power levels compared to regular MB engines. Still, the observed acceleration improvements in winter don't match the theoretical increased power predicted by the formula. Allowing for the fact that additional power doesn't produce proportional improvements in elapsed times the numbers are still around half the theoretical numbers.