I made 3 pulls on a dyno-jet dyno over the weekend. The car is all stock with a K&N filter. It has a little over 4,000 miles on it. I didn't plan to run the Camaro, but the other 2 projects I had in mind weren't ready. The first pull was 288.6 hp/307 lbft at the wheels. Pull 2 was 286.?? and 307.??. The third pull, I swapped the K&N for the AC the car came with. The hp was back to 288 and the torque was up to 311. The dyno operator mentioned that the engine was a bit leaner as well, indicating better flow with the AC. I've had the K&N on it for about 2,500 miles, it's clean and not over oiled. Does this surprise anyone?

I've heard that some people have those results. Look at it this way, more flow is not always better. When you take off the filter, the MAF goes nuts and the car won't hardly even idle. Don't know if it's the increased air or what.

airflow changes must be accompanied by computer changes, otherwise computer predicts one thing, and it gets another, freaks out, go into panic mode, and you get way less power than you started with.
MAF is made to deal with a particular airflow tract, if you change it, then the MAF calibration must change with it.

Here you go, read this! Or just skim through it

http://dieselplace.com/forum/showthread.php?t=117009

I would also think that heat soak would be kicking in by the 3rd dyno run?

heatsoak is a big issue when you combine a plastic housing with bad placement where you get no cooling (aka GTOs). it gets even worse if you have an integrated IAT sensor in your MAF housing, causing it to read much higher intake temps than what really occurs, pulling timing because of that, and reducing performance some more.

MAF's are very sensitive, and any mods will throw them off. my only mods were lid, filter, muffler and a z06 cam, and the car knocked throughout the full range of rpms, for any non-totally-lazy throttle inputs. all it needed was a MAF recalibration and the car literally woke up.

a lot of people think they're making things better, but they don't. what happens often is they add headers, which greatly increase airmass in midrange (aka peak tq already), and even with the computer's ability to learn and adapt, it will make it go lean enough that the car knocks, pull timing, and effectively becomes slower than originally.

yes, it sounds silly to retune things even in 'its just a filter' scenario, but the truth is that the computer is very eager to panic and reduce performance.

No, I'd be surprised if you experienced anything different. My son bought me a K&N air filter for my TA as a Christmas present, and I've never put it on. Everything quantative that I've ever read about them (on these cars anyway) shows less airflow than a stock paper filter.

I'm confused...your first pull was 288, then 286, then you put the stock filter back on it was also 288. It would seem to me that you're within the accuracy of the measuring equipment, taking into account the potential difference in a whole lot of variables.

Sounds like HP was basically the same. Since that peak probably came up around the 6k mark, it is probably limited by heads and valvetrain.

Torque was up, could indicate better airflow in the mid-range (4k-ish), where that number probably peaked, and where the heads and valvetrain weren't a limiting factor yet.

Engine was lean, probably indicates less restrictive airflow.

Maybe not a huge difference, but definitely a difference in the right direction...

Meaning that a relatively cheap paper filter probably does the same (or _better_) job than the more expensive oiled cotton filter.

The operator of the dyno felt that heat was something of a factor, and that if the first pull had been made with the AC, the hp would have been around 290.

the best test for MAF being miscalibrated is to turn it off and just run Speed Density