OTR18WHEELER

I understand the fact that colder air is denser and has something to do with combustion, but after a year of just thinking my 928 was underpowered for the huge 8" S4 wheels, It came alive today in low 60 temps, I got an unexpected tire squeel from a dead stop at a light this morning, and later on I achieved the slideways start that I missed. I'm wondering could my fuel mixture be off?

SeanR

Wish I had a better answer for ya, but mine runs much, much better when it's 60 degrees out than it does at 100. Today I kinda scared myself (again). It was in the 60's to 70's.

Mrmerlin

another consideration to include is rubber,
the tires will slide easier when they are cold a lil bit of dampness will also increase this sliding effect.

SMTCapeCod

COoler temps could also shrink some of the vac lines that could have a less secure seal. ANd are conducive to having the A/C off....

But yeah, it is all about denser charge, more fuel, more air, more power.

This is interesting- not vouching for it mind you:

http://www.csgnetwork.com/relhumhpcalc.html

My three-carb GTO loved fall....

dr bob

Air density is the deciding factor. The SAE "official" SAE method has slightly different baseline numbers, but the linked chart/calculator is fine for casual bragging numbers. Relative humidity numbers are an interesting factor, dropping density as the RH goes higher. Once you get to the point where you have fog droplets, the cooling effect of the water evaporating brings the density back up some. So a cool evening in the fog, Lion's Dragstrip near the harbor, lots of horsepower. Way back when...

andy-gts

how bout this........when air intake temps get above a certain point it then retards timing by 4 to 6 degrees....there is your power gain when cool air enters...!!!!

Chalkboss

Just better power through chemistry, physics. PV =nRT. I think... it's been a long time since I hit the books. If everything is held constant, lower temperature means higher density of air.

OTR18WHEELER

I agree with the rubber effect, but this was towards the end of a 100 mile trip at hwy speeds sustained at 60 mph+ (a few 90's got in there too), and mid morning dry pavement.

Jetdriver69

Works for the same for jet engines.

Cooler temps have denser air, so more power. However the higher the altitude, the thinner the air, the better the fuel economy.

Flying 47,000 ft, jet engines sip gas compared to 10000 ft, but also has much less power.

I'm just glad I'm not paying the fuel bills...but my carbon footprint is enormous

safulop

Yeah, come summer in Fresno my S4 stops being able to burn rubber on the big fat 265s. I call it "poor man's traction control." Something about the A/C + 120 degree intake temp + really hot asphalt just makes it sticky. You know one rule of thumb I read was that engine power is cut by 1% for each 10 degrees above 77 F. If you have 127 degree intake air (very plausible when sucking air from a Fresno roadway at 5 pm) you will see a 5% horsepower reduction. Combine that with the fact that asphalt you could fry eggs on will prevent your tires from spinning.

SMTCapeCod

Wait..so I'm physics impaired, but doesn't the forced induction overcome/render moot the density discussion?

Timing is a sound point to reference, too.

SeanR

Forced induction cars love cooler air. The denser the air, the more gets crammed in for ignition. It's why people go with intercooling, meth injection etc.

I'm not intercooled (yet) so there is a huge difference between the typical Texas 100 degree day and 60 degrees.

Bmw635

My SC BMW seems to have 50 hp more on cold mornings with cold blower before the housing warms up.

Tony

My car is a handful in the winter. Completely different animal under boost.

Fsharp9

These cars can run a little fat (rich) and I think the more oxygen in the the cool air helps perk things up