[basjoos]

One the way home this evening, I got in with a group of fast moving traffic and was able to run it up to 85mph and confirmed on the SuperMID and by the seat of the pants that I could enter and leave lean burn at that speed as I moved the throttle. It looks like, at least in my car with a Euro ECU and a D15B Vtec-e engine,that lean burn is only sensitive to the throttle position and not to RPM. Anything less than 6.1usec injector pulsewidth on a warm engine will produce lean burn. Vtec-e just kicks on at rpms over 2500 and has no effect on lean burn. I'm thinking that with a stock VX, the aerodynamic drag rises so fast that by the time you have reached 2500rpm at 73mph, the wind load is high enough to kick it out of lean burn and that's why everybody thinks when Vtec-e engages, lean burn drops out. Since that is not the case with my car, it will be interesting to find out what the terminal velocity in lean burn on a level highway will be. I'm guessing somewhere between 90 and 100mph.

Interestingly enough I was averaging 78mpg over the 5 mile stretch where I was running at speeds from 70 to 85mph. It was a section of gently rolling hills and the map shows no overall change in elevation for that stretch of highway. Now I just need to find how fast a constant 6.0usec on the SuperMID will get me on a level highway, but that will take a trip down to the Low Country and the flat roads of the coastal plains.

While down there I also need to get some mpg reading for various constant speeds and do some coastdown tests to measure my current Cd. I've made quite a number of small improvements to the car's aero since getting the Cd of 0.17 in coastdown tests 2 years ago, so my Cd may actually be less than that now.