I was just wondering what some target air fuel ratio and spark timining i should be trying to hit on a 2009 5.3 sierra. I am used to messing with the old style small blocks and just need some simple help.

 

Target air fuel ratio can be a bit of a tricky subject. As many hard factors can change it, and some times identical motors can be night and day.

The timing a LS makes max power at is 32 degrees advanced, but cam timing can change this around a bit. 30-32 degrees usually covers every thing I have ever read unless your going forced induction of some kind then you have to back timing off at a steady rate per PSI increase. Or for nitrous 2 degrees per 50 horsepower increase.

14-14.7 is ideal for part throttle cruising, and the closer you can get to 14.7 the better but don't go past. Total compression will dictate this one, but watch your knock sensor if you have one or keep your ears open for pinging. If you have less then 10-1 compresion and run 92 while you practice its not hard to keep the motor happy.

12.5-13.5 is usualy the fat spot for power and torque. This one is more dependant on total compression, cam timing, and ignition timing. A low compression motor with a stock cam will usually not respond to the 12.5 AFR, and actually can run stonger at 13.5. Then a high static compression motor with a big cam will need 12.5 to make the max power, and may actually ping if it get to lean under WOT.

Now you can factor in

What altitude you live as octane needs go down with altitude.

Total weight of the vehicle. Small motors and big trucks can cause pinging, but some deep gears can take the weight off thus lowering the chances of detonation.

Big rims and tires rather off-road or street 24's can factor if your going for a MPG tune. Power tune no worries since you would of fattened up the fuel curve.

Do you want a 87 or 92 octane tune. I hear the 92 tunes can actually save money at the pump when driving right.

Do you tow alot? If so stay away from the mpg tunes the lean fuel curve and fast spark table won't mix well. Try the power tune for towing the fuel curve works good for this too.

Heat, boy a good 110 degrees can mess with alot. I had a bolt-on 350 that was 8.5-1 compression take a dive past 100 degrees if I did not throw 92 in the tank, and even then it was doggy.

Cold, I just don't know. Here where I live cold is 50 degrees, and that is an Epic Fail if you really think that is cold.

Your stock computer will add a bit of fuel or take timing away to stop detenation, but its ability to change is not good enough to just be sloppy. If you wanna play the edge data, log till you get a good feel for how your actual truck re-act in the actual situations you actually drive.

 

14.7 AFR cruise 12.8 WOT and in my expierence I wouldnt go much past about 26 degrees of timing at WOT, it doesnt gain any power after that so what the point of pushing it, timing isnt everything

 

I learned on carbs, but the rules remain the same. I will be getting my own tuning software here soon, and I have been reading alot to get ready.

I used to have a MPG carb, and a power carb for some motors. Now I can just do that with some computer tuning, and down load different settings for what ever I may do.

 

Yesterday I was driving around datalogging and playign around and my wot afrs where all the way in the 11s. So today is trying to get the thing enough fuel. Thank you guys for the help.