Originally Posted by qzilla

That is interesting, I wonder what affect altitude has on these numbers? I know down here we get stupid IAT numbers in this dry heat and it has been HOT! I also wonder if the efficiency of the IC changes based on the Ambient temp? So at 90deg it might be really efficient but, at 105 it might loose a lot of that?



That is correct, sorry I think what I meant to type and what I typed late at night was confusing.

Most all temp sensors are resistive so lowering the signal raises the temp.




Cooler is not ALWAYS better. There is a too cool point and a too hot point and of course there is a sweet spot. The factory is worried about detonation, headgaskets under boost etc. So when they are really cold they retard the timing and when its too hot the retard timing.

Ultimately the ECM gets to decide how much timing to use. Boxes like the M3 change signals to get the ECU into that sweet spot for the greatest advance or efficiency.

There are a lot of factors going into this. On the M3 for the newer trucks there is actually several minor things we do. We run a little more rail pressure down low but, the peak remains completely stock. Anytime there is more pressure for a given duration it advances the timing. The flip side of that is on the upper end we tell it less rail pressure which causes it to change the duration slightly to compensate and it will also command a different timing value.

Same holds true for boost and/or IAT. Remember these are somewhat minor changes and we don't change them all the time, just when the factory readings get out of those zones.

Basically we are trying to stabilize everything regardless of conditions.

Same theory that people are doing with the resistors except we use "smarts" on board to allow it to change and adapt based on conditions, it is not a static change.



I also wrote on another board about changing the IAT while having another box on board that alters timing. I think there are some unique anomolies that happen there. A box may want to advance timing a certain amount but, cannot because of whatever the factory requirement is. You can only get away with so much of a change at once without going out of bounds. Well if yuo fool the ecm to change something with something like a resistor and then the ECU makes a change that is different than normal, your box could possibly in theory be able to make a larger change than normal resulting in unexpected results.

Basically they were looking at a timing box on a 2nd gen with an IAT fooler. Using that seems to all the box to advance timing mroe aggressively than on a stock truck because fooling the ecm also fools the timing box. So instead of a 2deg advance you might get a 3 deg advance.


Its all theory to some extent. It would be a lot simpler if there was just a manual they produced that said max efficiency = xxxx but, they don't!

I am certain different trucks, different air and different temps will all have slightly different results.

What we do know is that cooler air to the actual combustion chamber and more timing advance = more efficiency. Getting there is the tough piece of the puzzle.

Originally Posted by AH64ID

You cannot get a good estimate with a partial fillup.

Originally Posted by RamGazer

Hey Shorts, where about in the DFW area do you live? Me Frisco. Also what was your fuel mileage before (hand calc.) Is it higher now and by what percentage?

Originally Posted by RamGazer

The reason I'm asking about fuel mileage is I'm thinking about getting a Smarty Jr. But I like to do as much research as I can on different products before I go out and put some $$$$ down.

Originally Posted by RamGazer

My last fill-up of 27.508 gals. and drove 428.9 miles in seven days I got 15.6 mpg (all hand calc.) That is the best I've ever gotten. Smarty says if I drive easy (which I do to save fuel) I could get a 15% increase in fuel savings.