There are web sites that can give you this information with a little effort at searching.
For example:
Automotive formulas. It's a Hardley-Ableson site but the formulas are generic.
There's a link to air density calculation. Using your requested temperature difference (but the other params are pulled out of my butt),
80 ºF, 0% relative humidity, 29.92" Hg at sea level = 96.1 corrected air density (no units given).
40 ºF, 0% relative humidity, 29.92" Hg at sea level = 103.8 corrected air density (no units given).
(I presume the answer is percent of standard day, 29.92" Hg, 59 ºF, 0% relative humidity, sea level).
At standard conditions, SR20DE outputs 140 hp. At 40 ºF it makes 145 hp, at 80 ºF, it makes 135 hp.