The Effects of Ambient Temp on Acceleration

Last week I did a WOT at 85ºF ambient temp. This week I did a near identical run at 75ºF. Same location, same mods (3.4" SC pulley), same tune, same fuel (94 oct). Here are the results:



The 75ºF (yellow) curve does spin out a tad at the launch, but notice it stays ahead of the 85ºF (orange) curve the whole time, and starts to gain slightly up top. KR (not shown) was minimal for both runs. I plan to do more tests for 65ºF and lower temps to show the effects of colder air on our engines. Also will compare 3.3", 3.2", and maybe 3.1" SC pulley if possible.

was IAT the same?
it will be nice to prove how air temps change our engines dramaticly...nobody believes me when i say it feels so slow when its 90* outside.

quote: "was IAT the same?"

No, IAT was of course higher on the 85ºF day. This is the reason for the performance increase.

Below is the same graph, but including IAT curves for the 85ºF (red) and 75ºF (green) ambient temps. My IAT sensor typically reads close to true ambient immediately after a WOT run, and according to the numbers, my 85ºF day was actually 88ºF. My 75ºF day was actually 72ºF. I try to take the car out when it's exactly the right temperature, but sometimes things can change by the time I get to "the track".

Here's a new graph with a 55ºF run added:



The 55ºF run is using a slightly different tune, but I think the results would be the same as it's close to the old tune at this point. I'm seeing the lower temps are making less of a difference now. Time to drop pulley size...

Today I did another WOT run at 60F with the 3.3" SC pulley. Interestingly, the result was EXACTLY the same as my run at 55F with the 3.4" pulley (green line above). I was very surprised at how close they were.

Just shows how much ambient temps can affect your times... just 5ºF can make as much impact as a pulley swap!