I had a chance to dyno the G5 this weekend at National Trails raceway. I did two pulls and both were basically 510. Dynojet type dyno's are very repeatable, even across multiple locations and different operators. However, there are very few things that can cause an error. The typical error is usually:
1. The wrong correction factor, the SAE correction factor is the one to use. If you use the STD factor, the HP will be 2.7% higher than SAE. Take a look in the upper right corner of the printout, that will show the correction factor. In this case they used the right factor.
2. Environmental input. The Dynojet has three sensors, temp, atmospheric pressure and humidity. In general, the humidity has the most effect when viewing the typical range of inputs. In this case their hygrometer showed an input of 40 % humidity. This was during a six hour cycle of continual rain. The humidity was probably 100%. The dew point was over 75 degrees. The atmospheric pressure was also off, but, no where close to the error on the humidity.
These input errors probably created a HP number that was a minimum of 2% lower than actual HP. In my opinion, if you dyno your car on a Dynojet always ask for the DRF file or at least the data export file. The Dynojet viewer software is free and gives you the same graphical abilities that the dyno operator has.
3. The amount of smoothing used can typically increase/decrease the HP number. When I dyno'ed there was actually a contest going on. I believe over 30 cars were in the process of dynoing. To make everything easy the dyno operator had set up a "Smoothing Factor" of 5, that is max. This normally drops the overall HP of a dyno pull.
One last item about the Dynojet, it they use the factory a/f system logging software, the A/F normally reads leaner than actual. Even when the operator turns a/f smoothing off, it is not truly off. i have seen as much as 1 point diff at high rpms when you log in parallel with a high quality O2 sensor/system.
In summary, I was fairly happy with the 510 HP, that was probably 3-4% lower than actual due to the dyno's environmental input errors. I am guessing that the true HP on this day was in the range of 525-535. This is further supported by the car's MPH in the quarter. I had back-back 125-126 mph trap speeds with a Density Altitude (DA) of 3000. I will do a write up tomorrow about the details of the drag racing the G5.
1. The wrong correction factor, the SAE correction factor is the one to use. If you use the STD factor, the HP will be 2.7% higher than SAE. Take a look in the upper right corner of the printout, that will show the correction factor. In this case they used the right factor.
2. Environmental input. The Dynojet has three sensors, temp, atmospheric pressure and humidity. In general, the humidity has the most effect when viewing the typical range of inputs. In this case their hygrometer showed an input of 40 % humidity. This was during a six hour cycle of continual rain. The humidity was probably 100%. The dew point was over 75 degrees. The atmospheric pressure was also off, but, no where close to the error on the humidity.
These input errors probably created a HP number that was a minimum of 2% lower than actual HP. In my opinion, if you dyno your car on a Dynojet always ask for the DRF file or at least the data export file. The Dynojet viewer software is free and gives you the same graphical abilities that the dyno operator has.
3. The amount of smoothing used can typically increase/decrease the HP number. When I dyno'ed there was actually a contest going on. I believe over 30 cars were in the process of dynoing. To make everything easy the dyno operator had set up a "Smoothing Factor" of 5, that is max. This normally drops the overall HP of a dyno pull.
One last item about the Dynojet, it they use the factory a/f system logging software, the A/F normally reads leaner than actual. Even when the operator turns a/f smoothing off, it is not truly off. i have seen as much as 1 point diff at high rpms when you log in parallel with a high quality O2 sensor/system.
In summary, I was fairly happy with the 510 HP, that was probably 3-4% lower than actual due to the dyno's environmental input errors. I am guessing that the true HP on this day was in the range of 525-535. This is further supported by the car's MPH in the quarter. I had back-back 125-126 mph trap speeds with a Density Altitude (DA) of 3000. I will do a write up tomorrow about the details of the drag racing the G5.
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