Originally Posted by
presidential
The last statement holds true on a manual transmission. However, when dealing with a vehicle with a high stalled automatic (say 3500-4000 and above), the curves and results are very skewed. Unless the dyno can pre-load the vehicle, the stall can and will continue to slip aggressively causing the actual power numbers to read lower than they actually are.
Might want to ask the LS1 F-body guys about this one, it happens to them quite frequently.
That's mostly because a manual trans has a generally fixed (linear) loss due to friction. If that auto isn't locked up, it's slipping (duh) and throwing the extra power away as heat. Hence the need for tranny coolers. I've seen a similar thing happen on a Dynojet with a slightly slipping clutch. Numbers would come back 10hp low, 20hp high, etc. Then you pull up the rpms vs mph plot and it ain't straight!
