I'm very interested in figuring this out. I have a veepak reader and Dash Command app. It comes down to finding the time to do the somewhat controlled runs with each viscosity. I will also take video of the runs. The videos alone should show the differences, especially at highway speeds where the engine does almost nothing to accelerate when in 5th gear running the lower viscosity oil forcing a downshift for even the slightest of passing. On the higher viscosity oil, everything breathes, intake and exhaust are louder and the car can get out of its own way.... of course fuel usage goes up significantly too when it is driving this way. I suppose the logs should show the amount of fuel being dumped into the equation as well.@SiRDOHC how far does your interest in your topic go??? If you really are curious, pick up a obd2 reader that can log your oil pressure, throttle angle, rpm, and cam angle. Plot them against each other using different grades of oil controlling parameters such as weather.
If these do not provide the speed you need for logging, maybe pick up a sn65hvd can board and a teensy 4.x and whip up something that logs your pid's at high speed.
Currently it's running the 0w20 which is slightly thicker due to residual from the last fill (a 0W30Pennzoil LX, Mobil 1 0W40 mix), but the effects of the lower viscosity are still felt. I will be dumping the 0w20 out for a 0w40 as soon as I get enough data logged, as I can't stand the way it drives with it in there even in the colder months. The only reason I put the 0w20 in again is because my neighbor gave me a jug of it, so I decided it to put it towards this semi scientific experiment. I'll try to capture it in a clean jug and re-purpose it somehow rather than send it for recycle.
To be honest, I was skeptical too that the changes were viscosity related, I thought that the intake runner swirl flaps were jammed open or something.