TommyS401`

..more gas is being injected into the system? Someone was telling me that the car senses that it is cooler outside and it injects more gas to try to maintain a firing temp.

I was also told that really cool air isn't really that great for the car. Sorta made sense because he said hot air with gas will burn better and hotter rather than cold air with gas because the the fire won't be as hot.

so.. whatdayathink?

LCP

...and on top of that. A colder intake charge is less likely to preignite, so there is no detonation, and the engine runs more timing advance, allowing it to make more power as well.

Mike S

the reason a car runs better when it's cold is based on a few basic funtions. The first and foremost is that you are sucking in cold air, which is more dense, and the engine's MAF sensor, along with your oxygen sensors, can determine the air density, resulting in more fuel being added to keep the mixture accurate, which therefore results in more air and more fuel, casuing a larger explosion and therefore making more power. This is the same presmise Nitrou Oxide injection is based on. Many people do not understand that Nitrous is not flammable, but a cooling agent ( around -176 F neutral temperature), that allows a larger anount of fuel to be added safely. The mixure does often run rich on NO2, but you are stil gaining serious HP.

The other factor in cold weather performance is that the engine just runs cooler, as it is ingesting cooler air. You often see 10-30 Degrees cooler oil temp on an S4 in freezing and below weather.

Now, it is impossible to get your realistic top end in cold weather, as the air in far denser, and therefore the drag is higher, resulting in a loss in top speed, even considering the increase in HP.

This is effectively the same reason a golf ball flies farther in higher altitudes where the air less dense.

As for wanting hotter air in your combustion chamber in order to make more HP, this is pure bs and wrong. Many rally cars actually use intake manifold (no, I am not talking about intercooler injection) water injection, where a lite mist of water is injected into the intake manifold in order to bring combution chamber temps down and therefore make more hp.

I wouldn't listen to this guy about anything!


Mike S

S4_Cinci (I S'edTFA)

The more the charge expands upon detonation (ignition in the engine) gives more power. Cooler gas is more dense and thus will give greater relative percentage of expansion. Also predetonation thing is greatly reduced in winter - octane requirement decreases. Thus for a given octane fuel, more timing advance will occur with cooler ambient temps. But, gasoline does atomize better at higher temps., and cooler and more dense air causes greater aerodynamic drag on the car itself - so there is a bit of a trade-off with everything. All in all, more power in winter vs. summer all else being the same.

This is why people want to mist the intercoolers or use dry ice - denser charge! Also, engine computer measures mass density of air intake and injects exact amount of fuel needed, so more air (higher density) causes more fuel on a relative basis per combustion cycle. This gives more power per stroke which ultimately gives higher HP!

TommyS401`

I was thinking the same thing. I wanted to get some clear information from you guys.