For those that have tried to tune for a perfect a/f you understand that it is a moving target. Even if the barometric pressure and the coolant temperature are kept fairly constant there is still a huge swing in a/f for a move in IAT. This is extremely hard to track because the the true outside air and the engine IAT sensor do not see the same values because the engine ingests part outside air and part hot underhood air. There is typically a 15-20 degree difference depending on the type of intake system that is being used.
Myself and a friend have been logging most of the engine parameters for over two years. Recently I installed a custom intake that only uses outside air, therefore, the IAT sensor and the outside air are the same. Since I log on the same road and always in third gear the results are very consistent if the outside air temperature is the same or close. We probably have well over a couple hundred logs.
There are a whole bunch of reasons that the Innovate A/F logging system is one of the best, but, its speed and accuracy are amazing. I can make several runs at the same outside air temperature and the curves will lay right over one another with little or no deviation. I had a slew of 60 and 75 degree logs and was just waiting for the temperature to hit 90. I am planning to do three VEC cards, 60, 75 and 90 degree cards. I made a good 93 degree run today and here are the results. my target is 12.8 and that was achieved for 72-75 degree temperatures, but, looks what happens when the temperature goes up:
RPM 3750 4000 4250 4500 4750 5000 5250 5500
72 Deg > 12.80 12.80 12.80 12.80 12.80 12.80 12.80 12.80
92 Deg > 12.46 12.65 12.21 11.93 12.16 12.64 12.53 12.36
Change in A/F (0.35) (0.15) (0.59) (0.87) (0.64) (0.17) (0.27) (0.44)
% Change in A/F
-2.7% -1.2% -4.6% -6.8% -5.0% -1.3% -2.1% -3.4%
OEM Injector Correction Needed (mSEC)
(0.53) (0.23) (0.94) (1.43) (1.05) (0.27) (0.44) (0.72)
Obviously, hot air is less dense and the car will run richer, but, the computer should correct for the lighter air by pulling fuel, but, it seems the Viper PCM adds fuel at higher outside air temperatures and WOT, the change in actual air density is not close to the a/f changes shown.
Is there any way to post an Excel spreadsheet, if so I can put the numbers in a better format. i want to make some more 90 degree runs to make sure the data is consistent, but, there is no reason it shouldn't be.
This is a typical heads, header and exhaust car that dyno's (off the bottle)500 rwhp and 535 rwftlbs and is controlled by a VEC2. The absolute numbers may vary, but, the percentages will probably be close for a stock car.
Linear Mode
