Ok, winter vs. summer. I have an argument here and need the answer. Fuel/octane

[V6UnderPressure]

Ok, in winter I am under the belief that being that the air intake is cooler (like an intercooler) that the combustion requires more fuel for the compressed air. Or is it higher octane. I am at a disagreement with a friend here. I thought that the cooler the intake charge, the more chance of knock and detonation there is. Is thist true, or am I off?

Scott

 

[Ormand]

Heres an opinion...

I have more knock in winter than in spring/fall. Summer, the engine gets hot, that's a whole different story, plenty of power when I first crank it, then slows down as the heat gets to it. But in cold weather, two things work together. First, the inlet air to the MAF is cooler, which lets the charge stay denser as it heats up through the turbo. Then, the IC is working better, with the cold air outside, so the charge ends up even denser. The chip can compensate, to some extent, for the cooler air into the MAF, because the MAT measures that temp. But for most of us, there is no measurement of the temp into doghouse, (intercooler out). If you relocate the MAT to the doghouse, then you can maybe set up the chip to give a little less advance when the charge density gets higher. Anyway, that's my guess as to what happens-- you just have too much advance in cold weather, the ECM doesn't understand that you're getting more pressure. Probably some chips are better than others, but I don't have enough experience with different chips to really know about that.

 

[badboy86gn2]

Scott

I dont care what anyone says your car being turbo will run faster in the winter than summer

Dont beleave me tune the car and leave it even for the summer tune run it say 80-100deg then park it till winter and run it say 20-60deg i will assure you will go faster

heat kills our cars

Johnny

 

[ijames]

Scott, in winter the cooler air charge is denser so at the same boost the mass airflow is higher and you need to add more fuel to keep the same air/fuel ratio - if you don't you go lean. That's why winter is a double whammy; even if the airflow is the same you are lean, and the boost goes up from the increased ariflow (and other stuff I'm ignoring here) so you are doubly lean. Now, to support that increased airflow once you have increased the fuel flow to get the correct afr, you need higher octane to avoid detonation because your combustion chamber pressures will be higher. Here you get a slight help, because for every 30-40 deg F you lower in intake air charge temperature you raise the effective octane of the fuel one number (from 93 to 94, say). That's why we run 160 deg thermostats.

The mat is not used for fueling in the stock setup, only for small timing tweaks and to compensate the maf output (so I guess indirectly it is used but the maf will be pegged anyway so the point is moot (ignoring the translator)).

 

[Ormand]

Carl, I agree that the MAT is not used except to compensate the MAF, but the point is that there is no temp correction in the stock set-up. Bruce has done some stuff with relocating the MAT, and with the MAT actually in the manifold, it would be possible to correct for temp. Or, if you are running an extender, then you can use the measured MAF to control fuel and timing advance. It seems to me that my car responds to cold weather well before it pegs the stock MAF, however, if it ever does. (Stock turbo) The denser air will mean more "effective" boost at low/medium rpm, when the engine isn't pulling enough air to peg the MAF.