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If you are referring to the point where the plots from the two engines cross, it was at 2400 not 2600 rpm. If you are looking at that to determine which has more power or torque below 2400 RPM it is misleading. One engine was fuel injected the other had SU carbs. At the beginning of any dyno run, depending on when the recording starts, you see a ramp up of power as the throttle is opened. SU carbs
tend to hesitate when the throttle is suddenly opened and the air/fuel ratio plot shows that it went lean at the "tip in" point. A properly working FI engine does not do that. I wish I had a stock SU engine dyno plot to post as a comparison, but just do not have one. Without that we do not know how much of any difference at the "tip in" point is due to the difference between FI and SU characteristics.
You might also ask why we start the dyno plot at approx. 2300 rpm and do not record the power levels below that. The answer is the dyno is applying a constant load, the equivalent of driving up hill on a constant grade ( not counting wind resistance ). Just as you would not try to drive up a steep hill in 4th gear at say 1500 rpm,lugging the engine, we don't do that on the dyno. We actually start the runs on street engines at 40 MPH, as that is about the lowest that you would use full power ( wide open throttle ) in 4th gear on the road. Although we do tuning at part throttle, we do the recorded run as WOT as that is the only reasonably easy way to make an objective comparison from one car/engine to another. On a carbed engine, if I wanted to show the best power below 2500 I would probably use part throttle.
Using a dyno is a lot more informative than assumptions and "seat of the pants" comparisons.
John
V-Performance.com
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