Yesterday at the track in 93 degree weather my car was running slower than it usually does I beleive due to the high humidity/temp. I lost about 3-4 mph and 3-4 tenths. Can i tune for this by leaning the car out with my Diablo sport tuner. It looks as though i can lean it by percentages. What percentage can i go to. Can i read this per the MAF or O2 readings and what should they be at for optimum performance. The MAF reading look like it reads a ratio, at idle .90lt/m. The O2 reading vary of course, i guess i would have to read at WOT. Any help would be appreciated, thanks

 

The 02 will tell you if the AFR is correct. Most cars ,make max HP at 12.7. If you have a MAF it should read the air and give you the correct AFR for any conditions, IF everything is set correctly. If your AFR is off, then you will slow down. Beyond that... there is less air or less oxygen to burn on hot days, you will almost always go faster at night, or in the morning. I experience that in road racing, even with a cold track, qualifying in the morning is usually a second a lap faster than an afternoon race.

 

Thanks for the reply. Yes i just have to figure out how to decipher the AFR on my Diablo Sport Tuner. I can take a bunch of live readings i just am not sure which ones to use to read this. I get a MAP, MAF, O2, SPARK, RPM,MPH, and a few more i can't remember now. I can lean or richen up by percentages. I did not want to do it blind last night. It was about 91 degrees and very high humidity most of the night. Thanks

 

There's multiple aspects to this, some things you can tune around/for, some things you just cannot.

If the barometric pressure is low, you're just not gonna get airflow you'd get in normal conditions--that's bad. The good part about it is that everyone suffers the same from it.

The idea behind all these paramters taken into consideration during your airflow calculations is that while VE is constant for a given hardware setup, IAT, MAP, ECT will change, and you the changes are automatically adjusted for. The problems stem from the idiocy of most people, who consider that model 'too complicated' and start disabling/zeroing out all the modifier tables.

For example, you know your car can take, and doesn't normally knock at 130F IAT (staging lanes for example), but the PCM will pull few degs of timing, affecting the performance, which in the mind of a simpleton automatically and categorically that classifies as 'bad' and it must be instantly disabled. So such a schmuck will zero out the Timing vs IAT table so it doesn't do that anymore, repeats the run, sees no timing being pulled and a better ET and he thinks he's an ubertuner. Now the next time at the track it's even hotter, let's say 150F, and this time he again he actually could really use that timing to be adjusted for the IAT (and in that temp range most stock setups pull like 9*) and he knocks. He doesn't knock little, he knocks for the full 9* he should've pulled. At this point it's all up to luck, and how good the knock sensor system is (if he hasn't desensitized/disabled it as well already as it gets in a way of his brilliant ET's)

Let the computer do its thing--GM did spend a lot of time, money, and people way smarter than us here developing this thing. But you must understand which aspects of tuning (tables) kick in when, which are there to correct for weather, which ones are just descriptions of physical properties (ie. IFR) and should stay constant no matter what weather you got.

If you want to know what to adjust for weather, learn the limits of your car. How much timing can it take? When does it go into PE/OL? What are normal day-to-day variations, and what is abnormal and a sign of a real problem?

 

Thanks for the advice. I was not going to mess with the timing. I just thought if i leaned it out a bit it may run better in the humidity/temp. I did not want to do it blindly, that is why i was asking for advice/ past experience.