I read in a thread on the forum that the rich factory air/fuel ratio settings are conducive to buildup of carbon deposits. This makes sense to me, so wouldn't a proper tune, by optimizing combustion throughout the rpm range, result in a cleaner and happier ls3 in the long run? (though slightly less warrantied albiet)

 

I am no expert BUT with tunes people tend to want to get more out of their cars. This means that you will go in to get it tuned to run cleaner and prolong the life of the car... and when you get there you end up tunning it for the all out 1/4 mile drag!!!


The mod bug is a tough thing to fight



Rod

 

I did'nt have mine tuned for the 1/4 mile, it's not a drag car!

 

Not worth losing your warranty . Just my .02 cents .

 

I just went through a tuning process. While I am tuned for optimum performance it's all within normal parameters. The car runs well, upped my fuel economy and the exhaust smells "right" now.

So, not everybody tunes for all out performance.

 

At cruise, the PCM targets the A/F ratio at 14.7:1 which is stochiometeric. So that is not "rich". It monitors the O2 sensor so it can tell if its rich or lean. There is not much you need to do here since there is a feedback system (Short Term Fuel Trims and Long Term Fuel Trims) that were designed keep it on target. The 2005 uses a VE table to get the fueling close then uses the STFT and LTFT to get it on the money.

The PCM goes into Open Loop at WOT so it does not use the O2 sensors. It uses a table based on air mass and RPM. These settings are slightly rich at WOT to be on the safe side to avoid harmful lean situations and to keep the cat's from overheating to extend their life. Some tuners lean it out a bit by changing the Power Enrichment (PE Table) which only comes into affect near WOT to get the A/F ration in the 11.5 to 13.0 range depending on the mods. For the LS2, the factory goes into PE at about 45% throttle opening, but this can be changed if necessary. This is like the secondaries of a carb which comes into play at WOT.

Where the tune is conservative, in my opinion, is the ignition advance. Although there is a high octane and a low octane table and they both are conservative. I was able to add a lot of advance before any knock.

Keep in mind, these cars are rated at 27 mpg on the highway, so they really can't be that rich at cruise. People that have added a cam, intake, headers, etc. should change some of the PCM tables to get the engine to run the best it can under all conditions. Its relatively easy to get the A/F ratio right at WOT but where tuners earn their money is at idle, transition, and cruise.

 

thanks mez, awesome response. i know it's evident that i'm a newb at motors, but if you ever want to hear about feedback mechanisms in the human body......