Tune in 3rd Gear

[michaelmmoore]

I have an LS2 with twin turbos, 15 gph 50% meth, 50% water spray, 9 lbs boost, using the MAF, 6 speed. I am aware that tuning on a dyno is generally done in fourth gear, however, that works out to a bit faster than I want to go while tuning on the street. I have been tuning in 3rd gear and have A/F right in the 11.2-11.5 range. However, when I go to 4th the A/F ratio drops to 10.5-10.75. Is this difference normal? It would seem if I tune in 4th for an appropriate A/F my 3rd gear would be too lean.

Would SD tuning get me consistent A/F in all gears?

Thanks in advance for any comments.

[Redline MS]

I have an LS2 with twin turbos, 15 gph 50% meth, 50% water spray, 9 lbs boost, using the MAF, 6 speed. I am aware that tuning on a dyno is generally done in fourth gear, however, that works out to a bit faster than I want to go while tuning on the street. I have been tuning in 3rd gear and have A/F right in the 11.2-11.5 range. However, when I go to 4th the A/F ratio drops to 10.5-10.75. Is this difference normal? It would seem if I tune in 4th for an appropriate A/F my 3rd gear would be too lean.

Would SD tuning get me consistent A/F in all gears?

Thanks in advance for any comments.

Load is load so theoretically it doesn't make a difference as to what gear you are in. Just as long as you hit the desired load. If you look at the base VE table it is based upon "air load" and rpm.

[michaelmmoore]

I am not sure why I would look at the VE table if at WOT I am getting my fuel through PE.

[SSUte01]

I am not sure why I would look at the VE table if at WOT I am getting my fuel through PE.

Because it is effectively an airflow model for your vehicle, well at least to the PCM, exactly the same concept that a MAF is used to model airflow. The fuel is delieved based on an airmass calculation made by the PCM based on VE (and/or MAF), IAT, ECT, TPS, rpm and probably something I have forgotten. Make your VE/MAF table larger, PCM thinks engine is flowing more air and therefore will supply more fuel to maintain the correct (as you have set it) AFR. If MAF/VE is not accurate for your vehicle your Actual AFR will never match your Commanded AFR.

PE table merely determines the commanded AFR, using it to acheive the desired (actual) AFR in all but a few situations is IMHO (as I have learnt here aswell) is little more than an educated guess.

[HeadstrongMS]

Because it is effectively an airflow model for your vehicle, well at least to the PCM, exactly the same concept that a MAF is used to model airflow. The fuel is delieved based on an airmass calculation made by the PCM based on VE (and/or MAF), IAT, ECT, TPS, rpm and probably something I have forgotten. Make your VE/MAF table larger, PCM thinks engine is flowing more air and therefore will supply more fuel to maintain the correct (as you have set it) AFR. If MAF/VE is not accurate for your vehicle your Actual AFR will never match your Commanded AFR.

PE table merely determines the commanded AFR, using it to acheive the desired (actual) AFR in all but a few situations is IMHO (as I have learnt here aswell) is little more than an educated guess.

Exactly, The VE tables are real easy to tune all you need is a dyno with an Eddie current Brake and hold it at a load cell and tune it. If you contact the company that made your turbo kit and you tell them what other upgrades you have done the will most likely send you a starter tune then you can take the VE table etc from there and it will save you a lot of time tunning because every thing will be a lot closer.

[Redline MS]

I am not sure why I would look at the VE table if at WOT I am getting my fuel through PE.

These guys summed it up pretty good. Another name for the VE table is the "base" fuel table. It is the foundation of all fueling. If you get it set up right, the rest of the tune will come together nicely!

[michaelmmoore]

Thanks for the feedback. The car was tuned after the install by a "reputeable" tuner and I have been working on WOT. Guess I need to take it back to the basics myself (VE tables) and get it right.

Thanks again.

[Joe Lynch]

Thanks for the feedback. The car was tuned after the install by a "reputeable" tuner and I have been working on WOT. Guess I need to take it back to the basics myself (VE tables) and get it right.

Thanks again.

Log commanded and actual air fuel ratio and see if the commanded changed. If you don't have cat overtemp protection disabled, the commanded will get richer.

Turning COT off will keep the commanded from changing suddenly after a few seconds at WOT.

This may not be your problem, just something to check.

Joe

[JANNETTYRACING]

I have an LS2 with twin turbos, 15 gph 50% meth, 50% water spray, 9 lbs boost, using the MAF, 6 speed. I am aware that tuning on a dyno is generally done in fourth gear, however, that works out to a bit faster than I want to go while tuning on the street. I have been tuning in 3rd gear and have A/F right in the 11.2-11.5 range. However, when I go to 4th the A/F ratio drops to 10.5-10.75. Is this difference normal? It would seem if I tune in 4th for an appropriate A/F my 3rd gear would be too lean.

Would SD tuning get me consistent A/F in all gears?

Thanks in advance for any comments.

I see the same thing happen on the dyno, more than likely your going in to Cat Over Temp protection in 4th gear because it is a time thing, you get through the pull in 3 gear before the COT kicks in but in 4th your in it longer and COT kicks in which is fine.

I would not disable it but I would adjust it for around 10.8 if necessary.
We can also call this piston protection, because the longer your at WOT you want to richen it.