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Discussion Starter · #1 ·
I wanted to share my dyno results along with some dyno related facts. My results were impacted by a correction factor error and I’m sharing the information I’ve learned to help others understand the data & parameters associated with a dyno run.

Most of us dyno using a Dynojet or other inertia style dynometer. The inertia dyno is one of the more accurate & repeatable dynometers compared to a Mustang or brake dynometer. Mustang dynos require the operator to control a braking load to measure horsepower. This load can be affected by operator error along with how tight the car is strapped down. Inertia dynos measure the acceleration rate of drums powered by the car. This virtually eliminates operator error unless the car is loose or strapped down crooked.

Any dyno results are affected by the current atmospheric conditions. These conditions are used to correct a given reading to a standard set of conditions. This is commonly referred to as the SAE correction factor (there are many others such as DIN, JIS etc). It’s important to know what your dyno conditions are & verify they’re correct. The newer Dynojet dynos use a weather module to record the ambient temperature, relative humidity & absolute pressure. The operator has NO control over these readings, other than module location. It should be noted that absolute pressure is barometric pressure corrected for elevation above sea level.

The SAE correction can be calculated using the Engine Tuner’s Calculator It's interesting to see how all of these parameters interact to affect the CF. Absolute pressure & temperature are the largest factors. The absolute pressure (or station pressure) can be calculated from the barometric pressure & station elevation using this Station Pressure Calculator Unless you’re at a high altitude, the absolute pressure should be within 1 in-Hg of the barometric pressure. SAE correction factors outside the range of 0.90 to 1.10 should be questioned. In my case, the correction factor was 1.26. This CF error was caused by bad pressure readings of 24.63-24.84 in-Hg. (see attached) I used the calculators above to determine the correct SAE factor was 1.034 based on a absolute pressure of 29.06 in-Hg.

Dynojet has a free downloadable Dynojet File Viewer This viewer can be used to plot & change your dyno data files. Dynojet recommends using smoothing = 5 for dyno run comparisons. I used the viewer to plot my data uncorrected and applied the proper SAE CF of 1.034. It should be noted that once the data is stored with the run parameters, it cannot be changed. The file viewer is awesome, you can change the either axis to suit your needs & change the parameters displayed

My final numbers were (boosting 14 psi):

Run #1: 232.19 * 1.034 >> 240.08 HP; 259.04 lb-ft TQ
Run #2: 235.54 * 1.034 >> 243.55 HP; 253.63 lb-ft TQ
Run #3: 225.02 * 1.034 >> 232.67 HP; 263.31 lb-ft TQ (starting to heat soak, IAT 100+ deg.)

Overall Im happy :clap: with the numbers I got with my mods. I was part of the 300 HP club for awhile until reality set in :crying:

To summarize, here’s a dyno checklist which should help prevent you from getting owned by a correction factor:

1. Have the operator display the graph with ambient conditions & SAE CF, smoothing = 5. Perform reality check, CF should be close to 1.00.
2. Plot data uncorrected data, smoothing = 5
3. Get the data files before you leave.
4. Download the Dynojet viewer & check out your data files after you get home.
 

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you thought you had 300+ with just stg1 and exhaust? cause i'm sure we all know by now that plugs, wires and catchcans and even CAI's don't do a bit of difference.....
 

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Discussion Starter · #4 · (Edited)
yarbsea said:
you thought you had 300+ with just stg1 and exhaust? cause i'm sure we all know by now that plugs, wires and catchcans and even CAI's don't do a bit of difference.....
Come on now :frogtongu That's what the dyno chart said. I knew it was BS, it just took me awhile to figure out what the problem was. Correction factor was 1.26 * 235 = 296HP :wah?!:
 

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Good informational post. Great way to educate!!!!!! Thanks for the research.
 

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Discussion Starter · #6 ·
Some more info....

Here's another interesting fact. Since the Dynojet is an inertia dyno, the results CAN be affected by wheels and tires. So if you doing comparison dyno runs before & after mods, be sure to use the same wheels. A lighter wheel/tire combo could show up as more power & torque compared to your last run.
 

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yup you are correct on everything...

our (New England Dyno) usual SAE correction runs between .97-1.06 and we are at 476ft above sea level.

Uncorrected will always be 1.00 (used to be called "Actual Horsepower" on WinPeP 6 and under).

for us there hardly a difference between uncorrected and SAE corrected on a nice sunny day, but bring in the heat or rain for get it. we see up to 1.06 CF!

to really compare a run use uncorrected so the system will not apply the weather effects to the actual numbers. This is because you most likely will not have the same weather on 2 different days.

now if the temps go below 77ºF the correction factor will go down to like .99 CF. and thus the power numbers will go down.
 

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Correction factor of 1.26 is nuts. Did you dyno on mount everest at a temperature of 100 degrees?

For reference, ACX's dyno's were at a dyno that was about 2500ft.
 

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Discussion Starter · #10 ·
Bad pressure reading...

The 1.26 CF was caused by a bad weather module pressure reading. That's the point of this thread...just because the computer said it's so, doesn't mean it's correct. I was at 1067 ft.
 
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