Thought it might be a good time to discuss some dyno testing How To's. I always use my own weather station during a dyno session. Then I do the HP corrections using the new SAE method myself using the dyno raw values. Keeps everyone honest! Don't use the what is called the Standard (STD) HP correction method. Its really the old SAE method but produces artificially high numbers.

For chassis dynos, always do a pull in 1:1 gear, with the hood open, with a cooling fan blowing on the grill. Make sure the oil temp is up to normal. Do all comparative pulls at the same water temp - thermostat set point. Allow cooling time between runs.

For OBDII machines.
- Desired WOT AFR is achieved by long term fuel trim at part throttle plus fixed fuel increase (O2 sensor is only accurate at 14.7 AFR).
- Factory tune at WOT is rich for cat con longevity.
- Any increase in airflow leans AFR.
- Most of the observed HP gain is the result of a leaner WOT AFR.
- After some normal driving (~100 miles), most of the observed HP gain will be trimmed out by the ECU.

 

You are SO exactly correct. (almost)

I disagree with leaving the hood open during the pull however, it greatly exaggerates the gains from the now-common open cone filter kits.

If the BMW M3 guys followed your advice, a lot of them would be better off.

You can't believe the piece of crap from a company called AFE that they all spent big bucks on. Its one of those made in Taiwan intakes (even though they say they're made in the US)
Dynoed by a vendor with a vested interest it made 10 hp (with the hood open). Later it turns out that the M3 is running at 15.6:1 after adaption. After many complaints about stalling, even when pushing in the clutch on the freeway (!), a few people have started to realize that all this "R&D" that made the kit so expensive, was just a sham, and that the cars LOSE hp.

If the M3 was dynoed properly, as you describe, a lot of guys would have been saved a lot of heartache.

http://www.afefilters.com/5410461.asp :notnice:

 

I have seen abnormal losses on turbo cars with the hood down. I could be convinced that hood down is more representative for non-turbo cars. I would measure the air temp rise under the hood during a pull.

This becomes real important because there is a 1.09% drop in HP for every 10 degrees F temperature increase.

 

The major point that I was trying to make is:
Do baseline pull and correct numbers with SAE method.
Do THE modification.
Drive car for a couple of days to let ECU retrim.
Do evaluation pull on same dyno and correct numbers with SAE method using same weather instruments.
The results will truely quantify the change.

 

This is the weather station that I use. It will measure temp, humidity, and baro pressue......and calculate SAE corrections. I also have the download kit that allows the box to talk to a PC. With the logging and graphing software (part of the download kit) running on a laptop and the RaceAir unit close to the engine air intake, I can monitor conditions under the hood during a dyno pull or on the road.

The same unit will also calculate a dial-in at the track and correct ETs to SAE standards for performance evaluations.

http://www.computechracing.com/drsystem.html