cool weather tuning

[gnturbo]

I have been tuning my car in the summer with air temps as high as 120 on the scanmaster.Now the air temps get as low as 50 in the morning and man does she fly .Just wondering if there are any adjustments that come with cooler weather.I started to get knock last night when I had tuned it all out a week ago.

 

[bruce]

For some reason GM thought it better not to use the IAT timing correction, so there is some room for temp related detonation problems.

While not a problem on the stock tune, it can be as you dial up the boost.

There is also the difference as the nation changes from summer brew to winter gas.

Raise the octane a couple points dial the boost down a little are the easy answers.
Better answer is reprogramming the chip for the changes.

 

[NASSTY]

My friend whom I refer to as the "Guru Of GNs" says in cold weather turn up the fuel pressure 1 or 2psi.The car sucks a lot more cold air than it does hot humid air in the summer months.So a little more fuel wont hurt anything.Or you could dial the boost down alittle like BRUCE said But thats no fun.

 

[bruce]

Originally posted by 2NASSTYBUICKS
My friend whom I refer to as the "Guru Of GNs" says in cold weather turn up the fuel pressure 1 or 2psi.The car sucks a lot more cold air than it does hot humid air in the summer months.So a little more fuel wont hurt anything.Or you could dial the boost down alittle like BRUCE said But thats no fun.

Trouble with that is that it just covers up the problem rather then curing the problem. The problem is timing, the MAF does compensate for the difference in air temp, and air injested into the engine.

If you were to measure the MAT in summer weather you'd see in general that the MAT was about 40d less then coolant temps in cruise conditions. In the winter time, it can be 60d cooler. Now, if the air fuel mixture is being compensated for, the only variable left for error is the timing. For the new guys, in hot weather you add timing, in slight amounts to make up for the lessening of air density. And in cooler weather you LEAN down the motor, again slightly due to the increase in exhaust back pressure.

Lots of variables, and lots of info distilled to a very short paragraph. Doug Roe in the QJet book, and Dr Jacobs in his cover the material in more detail. Along with various NACA documents. Reading thur the 8D GM Mask points out the IAT fuel corrections.

 

[blackbuick87]

Originally posted by bruce
And in cooler weather you LEAN down the motor, again slightly due to the increase in exhaust back pressure.

With a given amount of timing shouldn't it be richen the motor in cooler air, due to the air being more dense, so you can keep the a/f ratio the same as it was in the hot weather?

 

[strikeeagle]

I thought the sole purpose of the MAT was to correct for non-linearity of the MAF at temperature extremes. That is, to my knowledge, it does not bring about "enrichment" when Fall rolls around.