Quote:
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.