| speed-density setup has a large transient response time and it is subject to picking up heat from the intake manifold and skewing the A/F. Mike Vale's TT had a VPC in it, which uses speed density. On the dyno while tuning, if I let the car sit and cool down for a period of time, when I made the next dyno run without changing anything in the ECU or the VPC console, the A/F would change by about 0.5 points of A/F. It seems to me that its design is less accurate because of this. I recall, back in Gainesville a friend of mine did a turbo conversion on his 1970 240ZX where he put a built L28 in it, the 2.8L inline 6-cylinder, but he added a turbocharger to it. 8.5:1 compression ratio. He used a haltech on it and while he was tuning it I recall his frustration about the A/F not staying the same. He was continually 'chasing' the A/F plot. In another dyno-session involving a TT with a VPC, customer's name I can't remember at this moment, I was also having issues with getting the A/F plot to stabilize. It continually wanted to shift up or down dependent on how many pulls back-to-back that I made. Perhaps my experiences have been bad examples of the speed-density setup; I only speak from what I have seen.
*shrug*
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