It would be cause for concern, if a 20-40RWHP/TRQ difference presented itself with runs on same dyno. Based on your 11.9RWHP and 9.41ft-lbs TRQ difference in numbers for your three dyno runs, which isn't noticeable in the seat, I would say the runs went as they should have with just small factors/mechanical engineering playing a role on how the car performed on the dyno.
With Dyno pulls there could be one or multiple contributing factors to the variation you see in RWHP/TRQ. We can rule out increase due to torque converter lockup since you have a 6spd. Since your TRQ ranges for the three pulls are within (417.07-426.48) 10ft-lbs of each other and having a custom tune through H/F, you can rule out the tune being off. Unless, ignition timing and A/F ratio is off, but doesn't look like it. To bad you didn't get another pull after the last and final pull which produced the greatest RWHP.
However, I will put my money towards my assumption on the "warmed-up" scenario and contributing factors below:
Usually, dyno testing starts off with a vehicle at normal operating temperature. If your car was started cold, partially cooled down, or already warm but not on WOT runs. After the two pulls, the engine components and mixtures were then probably at optimal operating performance/temps. Thus leading to maximum engine performance and on your third pull gaining 11.9RWHP.
1. Keep in mind, the electric control unit (ECU) uses the information it receives from the engine coolant temperature (ECT) sensor to operate or adjust timing and fuel mixture for it to run at its optimum level. Depending on what your ECT sensor was mechanically reading, adjustments may have been made by your last and final run.
2. When warmed up/hot, the fuel is less dense and therefore the ECU will compensate for a less dense fuel by injecting more which is when you see the A/F range drop on the dyno chart at WOT. A less dense fuel is more prone to combust and therefore will combust much easier and faster which may be why you see the not big but slight vartions of a mild vs. steep curve in A/F ratio.
******If "heat soak" was considered, it would be more geared towards losses than gains. I would think if this was the case, the ECT sensor would have picked this up and kicked on the cooling fans as well to eliminate the heak soak factor.
In regards to what Perfracer was saying:
1. Some dyno shop owners with the Dynojet graphs, have been know to perform "smoothing" calibrations on the dyno reading from 0 to 5 with 5 being the highest amount of smoothing. The smoothing function flattens the mountain peaks along the power curve thereby adjusting the HP reading. The little peaks you see in the power curve can come from slight jerking motions of the tires on the dyno rollers due to unoticeable slack created due to the immediate pull/torque. Most dyno owners, make runs without "smoothed" curves so you can know truly and how efficient your engine runs. Smoothing can vary power readings by approximately 10HP.
2. Dynos that also have the option for vehicle inertia correction, a "sneaky" operator can take this route and enter faulty information to specify inertia value for your vehicle which will lead to the alternate RWHP/TRQ readings.
Each of these two actions can be done in a matter of minutes between runs. NOT saying any of the two dyno adjustments above happened, just in response back to Perfracer.
By all means, I am no expert on tuning a car or running a dyno. This is all just from my basic understanding, asking questions, knowledge extended to me by my buddy who owns the dyno shop and buddies who have had this question arise on many other occasion at our HEMI dyno events.
Sent from AutoGuide.com Free App