Interesting ...

I was never able to run more timing with my new FMIC. But, it's not an amazing piece of work and I installed it in the middle of the summer when temps were around 105º. I was already running a bit of timing.

I have noticed recently that I still run a little more timing than other IXs with the stock FMIC. Given that, it opens up an interesting idea ...

How can a more efficient FMIC allow for more timing and a denser intake charge require less timing at the same time?

I see both in my own vehicle and it is quite interesting.

I think it touches on both of our arguments ... Cold, dense air makes power. Hot air robs power but burns slower.

I need to learn a little more about air properties in the winter and summer before I can come to a conclusion on this. I feel that it has to do with the oxygen concentration in the air, but I honestly don't know the science behind that.

 

Thats a given, being that S/C cars suffer from heatsoak more then a turbo'd car

 

bump. I wanted to keep this thread going. Interesting topic.

 

I can attest to the fact of having more knock on my '03 during the colder winter months than during the warmer months. When I first tuned my car it was still around mid-70's and the occasional 80's ambient temp. Now that it's been into the 20's and low 30's I had been seeing knock popping up all over my map. The car seems much faster during the colder months, and even with the reductions needed in timing really hasn't affected it. Colder air does produce a denser charge, as the molecules are clustered closer together. Think of it in terms of water and ice...water by itself in an ice tray is very fluid (obviously lol) and you can over-fill the tray because...when the water freezes the molecules "contract" next to each other (or become denser for lack of a better word) and the ice cube is now at a lower level than it originally was with water. Same applies to air.

 

I would have thought the problem with winter is you hit higher load cells, which may not be tuned properly???

 

I have only noticed coolder climates making knocks only in the very low RPM load range. That is what I have been seeng in my logs. I am using a modified JDM Mivec map so im sure that has something to do with it because when I changed it only the knocks went away in the same whether.

 

Here is what I found ...

I tuned my car dead on in the summer. Mid day temps were around 100º+ and evening temps fell to the mid 80º range. I could run quite high timing values ... Here is a log from June ...



Now, after it cooled down a bit I noticed some knock occuring. And, strangely, it seemed (according to timing values) that I was actually hitting LOWER load cells than my 2-byte load was showing.

I was at the drag strip in the summer and had the occasional 1 count of knock show up. After it cooled off to the 60ºs at night, I saw up to 9 counts up top in 3rd and 4th. Timing registered up to 2º MORE than it should have according to the 2-byte values. I think this is due to the standard 2-byte data not using barometric pressure and intake temp for the calculation (as JB has found recently).

So, in comparison to the graph above, I now run ~2º advanced at peak torque and ~10º at 7000 to avoid knock.

 

you are on the right track with the water analogy, but water(h2o) actually expands when it freezes... Think of what happens when you put a water bottle full of water in the freezer.

I don't have any more to contribute right now, but i might be able to do a few logs in my car today... Just downloaded(don't know it thats the right word) the new No Lift to Shift feature for ecuflash.

I'd still like to see some winter logs from touingbubble just so we can compare.

 

Yeah, you're right...just thought about that lol. Late night last night, wasn't thinking clearly. What I meant was that when it gets colder it forms a denser mass and the same thing applies to air. Good catch.

 

I've got some but not already posted ... I copied that one over from a post back in June. If I get an early day today I might make some pulls and post results.

I'll bring this up again in this thread ... I think that the temp compensation table has a bit to do with what we are discussing. Does ANYONE know EXACTLY what the table does? Is it a load offset? Airflow offset? IAT modifier? I've changed mine with some success based on recommendations from a fellow tuner, but I'd love to know what it really does ...

 

That would be some good information to know. I had always assumed they were for a fuel compensation, as a denser charge of air requires more fuel. But now that I look at the table it only says "units" so it could apply to anything.

 

That was my initial thought as well. But, after thinking about it for a while, it would make more sense to alter a value that keeps the load in the same place throughout the year.

 

I'm asking a couple of meteorologists about this ...

 

Alrighty ... meteorologist #1 isn't 100% certain, but she believes that there is no difference in the molecular composition of the air between summer and winter. The only difference is molecular density.

For clarity, I specifically asked ... If you take summer air and compress it to the same density as winter air, would there be a difference in the oxygen content between the same amount of the winter air and the compressed summer air?

 

Something just hit me ... not sure why I didn't think of it before ...

The ECU has no way to compensate for intercooler efficiency because the IAT sensor is in the MAF. However, it can compensate for air temperature changes via the temp compensation map. This is the difference between increasing air density via the intercooler and denser air at the intake.

So, my theory is that the temp compensation table is modifying a value that is throwing something out of wack and causing this knock. Therefore, understanding this table could be the key to a solid year-round tune.