Dyno'ed my 99 GTS - Graph inside

[1.8t]

Setup is K&N replacement filters, smooth tubes, M&M headers w/ testpipes, and a 3" Corsa Exhaust...the car does not have a tune.

The dyno is a dynojet 248C SAE corrected. I kept all 3 runs on the page so people can see the difference that IAT's and coolant temps make on the stock PCM.

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Run 1 in green after a 45min drive to the dyno. A little bit of un-assisted cool down(no fans) in the parking lot while they got the dyno ready. Note the A/F ratio on this pull.

Run 2 in red and was done about 10sec after run 1. The IAT's/coolant temperatures were hotter than the previous pull and the car compensated with a lower a/f ratio to prevent any detonation.

Run 3 was a 45 min cool down with 2 fans blowing on the radiator/intake the entire time. Upon cranking, the pull was done within seconds. IAT's and coolant temps were a good bit lower on this pull and the multipliers at these temperatures were quite small(possibly adders even, not sure since I have never seen the tables within the OEM PCM), hence the pretty lean A/F ratio.


Anyways, final power pull numbers were 444whp and 479wtq which seems to be in the ballpark of most others. I just thought it was interesting to watch the factory PCM and OEM settings juggle the A/F ratio based off the data it was receiving from various sensors.

 

[99 R/T 10]

Those are some pretty strong numbers. Congrats!

 

[Jack B]

I have done close to 100 dyno pulls and have never seen that large of a variation in a/f when you put the a/f sensor in the oem sensor ****. The variation is more likely due to the use of a tail pipe sensor or a sensor that is past end of life. The viper PCM main modifiers of a/f in open loop are coolant temp and intake air temp. The intake air temp being the largest modifier. It would be unlikely that intake air temp could change that dramatically in a short time to alter the a/f as shown as your log. If you look at the green a/f log at 3400, you will see a one point aberration, that is virtually impossible with all the smoothing that is used in a dyno's a/f scheme, that points to a faulty location or sensor.

In summary, most dyno shops have a/f readouts that are very suspect.

 

[1.8t]

Location was at the tailpipe so that could be the culprit.