Originally Posted by lobuxracer

It won't change timing at all. It will change injector duration, but ignition timing will remain where it should be once the coolant in the engine's water jacket stabilises at 82 C.



The ECM will add the correct amount of fuel for the amount of air entering the engine as measured by the MAF and corrected by feedback from the WB O2 sensors on each side of the engine. It will not change ignition timing. That's not how it works. Timing is based on combustion chamber design and engine operating temperature, not air temperature (unless the engine is air cooled, then you're screwed for fuel AND timing because the engine's operating temperature is unstable.)

Water cooled engines maintain a relatively stable cylinder head temperature - once they are at operating temperature. The problem in cold weather is it takes longer to heat soak the head, cylinders, pistons, and cooling system. The energy used to get these items up to temperature is NOT used to rotate the crank, so it is completely lost.

This gets at one of the fundamentals of engine operation - every heat cycle is followed by a cooling cycle, and everytime the ignition fires, some of the heat of the reaction is lost to reheating the engine's components and cooling system. The ideal engine would have its components completely thermally neutral - not adding or subtracting any heat from the chemical reaction, but those materials don't exist today.

That heat is both lost efficiency AND lost power. If the heat is absorbed by the cooling system and carted off to the radiator, then it surely didn't push on the piston and give us kinetic energy to move the car. The colder the starting temperature, the more energy will be lost this way.

The other issue with outside air temperature is it doens't vaporise fuel very well when it gets colder. Yes, I am keenly aware that fuel injectors spray fuel into tiny droplets. I'm also keenly aware that those droplets will combine if the intake air is cold, and bigger droplets do not burn as efficiently as smaller ones do. With the GDI in the ISx50s we get a BIG plus for efficiency because the fuel gets injected directly into a very warm cylinder instead of being splashed on the backside of an intake valve in hopes of gaining some heat to assist vaporisation. Still, the colder the intake air, the more fuel gets "wasted" heating the air from its initial temperature.

If you look at the super efficiency engines, you see the engineers very carefully control intake air temperature to acheive low brake specific fuel consumption. And they like the air to be as warm as it can be without promoting detonation. Ideally, you need control over air AND fuel temperatures to get maximum efficiency (and if you think about it for a minute, you need precise control of the same things for maximum power.)