Okay, so a few weeks ago I had my car on a chassis dyno (Dynojet). I made two pulls. Mods are a lid and a Corsa catback.

On the first pull, I put down 325hp and 343tq.

On the second pull, I removed the stock paper filter from the airbox. I lost 7hp and the A/F (measured at the tailpipe) went lean.

To me, this indicates that without a tune to add in some more fuel, going to a K&N filter would NOT be a good idea.

Am I correct? If not, what am I missing?

 

first off, there is a big difference between a k&n and nothing, secondly, if you were in closed loop, i believe over time it would correct your long term trims enough so that it would be fine, although technically, you should have a tune after each modification in order to get peak performance from it.

 

The stock PCM makes adjustments over time? I had no idea...

 

well not specifically to wot, but it would at cruise and part throttle, which would be fine with a k&n

 

Ask Psychocabbage about his experience dyno-ing with a K&N and then a factory paper filter . You might be surprised .

As far as losing 7 HP on the 2nd of 2 runs, that seems a little strange, but how much cool down time did you allow in between? I know on the 2 occasions I've dyno'd my car, the first run has always been just slightly lower (although the last time I dyno'd, I didn't change anything in between pulls, allowed maybe ~10 minutes cool down, and the 2nd pull was about ~1 HP & 1 ft-lb higher).

Perhaps the computer just didn't have enough time to respond to the extra airflow going through the MAF, and didn't increase the fuel accordingly? Maybe it would need a "learning curve"??

 

There are other factors going on that may have been a reason why you had a lower 2nd pull. As mentioned above, the computer adjusts fuel, spark, etc. for various conditions. If for some reason the knock sensors were tripped and timing was pulled during the run, that could be the source of your lost power. The lean condition you saw without the filter could have been the culprit too. Either way, with just a lid and a catback, your fueling most likely is only off by 2~4%. With as rich as these cars are from the factory, that's nothing. 2~4% is well within the limits of the PCM to make adjustments.

Also, I have a hard time trusting their WBO2...especially with it at the tailpipe. My WBO2 was in my header collector during my runs and read .5~1.0 richer each time than the shops WB. That plus the fact that you still have cats will affect the reading too.

 

Imagine the timing of all this. I *just* went through all of this yesterday. Brought my 1999 Z28 up to the dyno, bone stock it put down 293HP/309TQ at the wheels. After I added half a degree of advance at WOT from 3000-6000, we raised the power to 298HP/313TQ. Then we installed a K&N air filter, and raised the power to 302HP/316TQ, but adding the K&N richened the mixture from about 13:1 to 11.9:1. If I tuned the AFR to 13:1 I bet I'd get another 5HP or so.

Is it possible running with no airfilter causes the MAF to improperly meter the incoming air? I thought I read somewhere this can happen because the air goes through the MAF too quickly. You could determine this by datalogging the MAF's signal output with an air cleaner, and without (E.g. if the MAF is reporting lower airflow when all else is equal without the filter attached...)

 

Nice numbers there Jake

 

If there's any issue with the MAF and no filter, it's due to the change in airflow characteristics. Not too much airflow. Boosted cars run 7+psi on these MAFs. The filter (and MAF screen) helps distribute the airflow evenly across the MAF wires. Remove one or both and you lose that consistency. Also, the MAF is very touchy to modifications in the airflow of the motor. Once you calibrate it for the current setup on the motor, it'll run great. Change the airflow characteristics by adding better breathing components (lid, exhaust, etc.) and you'll need to change the MAF table in the PCM as well for it to fuel accurately again. Since not everyone is a tuner, the PCM has some room for adjustment by adding/subtracting fuel trims. Only thing is, the trims learn under normal driving. As soon as you give it enough throttle to activate power enrichment (PE), then the PCM goes into an open loop fueling mode where it doesn't learn....it's pretty much assuming the actual AFR equals the commanded AFR. If there are positive fuel trims at part throttle, they can carry over to open loop based on the assumption that WOT must be lean if part throttle is lean. However, the PCM won't subtract fueling from open loop if there are negative fuel trims.

Make sense???

 

Thanks everyone for your input.

Capn Pete -- The car rested maybe 1-2 minutes between the pulls. I never shut off the engine.

 

OK.. Im here.. hehe

K&N and No Filter netted me the same exact result. A loss of 3rwhp. EVERY TIME.. Regardless if I had a lid on the car or the stock intake..

So why is that? First, let me say some of this is just my theory..
I think that all too often we take somethings to mean more than they should. We think because we understand that nothing should = no restriction.. so if there were no filter, then there should be limitless amounts of air free to flow at the engines whim.. but... what seems to really be happening is that the air it is sucking in is not smooth enough for it to do anything really specatcular with.. This is something that is definately appearant on the LT1 cars with their airfoil. Once added you see a slight gain in power.. Regardless of intake method. Reason? Air is manageable.. Seems to be a key to our COMPUTER controlled cars..

Learning.. I hear this all the time.. The cars need time to learn.. This was the case with the L98's and their Speed Density system.. No longer on ours.. Ours just do it out of the box.. if not, there is something wrong..

I did 2 sets of tests.. I rented the dyno out for 1 hour each time.

On the first, I went in and strapped up and just started swapping filters and then lids... I came in bone stock and did runs back to back.. All of my numbers were nearly identical.. I had one run where the car went into open loop (a fluke) and produced an anomoly. That run pushed the HP way over all the others and the A/F went to near perfect. Again. .Not something it does normally without any tuning..

Then for the next series of tests I returned a month or so later after having been driving around with a K&N Filter (this was done to dispell the "learning" theory).. Results? EXACT Same. .Car pulled identical numbers repeatedly.. Filters and lids were changed quickly.. How quick?
I could do a pull at say 12:00:15 and its next pull would happen at 12:00:45. I would then swap filters and that pull would happen roughtly 1 1/2 min later. Back to back to back.. Lid changes took me all of 3 min tops..

Results?
Stock lid and stock paper filter made 3rwhp more than stock lid and K&N, Amsoil or No filter at all.

Aftermarket Lid and stock paper filter made 8rwhp more than aftermarket lid and K&N, Amsoil or No filter at all.

What did that tell me? That #1 a Lid is a definate imporvement in power and #2 the stock paper filter rocks.

Dont believe the marketing hype..
The whole concept of "reoiling" a filter is lost on me. Spend 3 hours of your life changing a filter on your car or spend 1 1/2 min putting a new filter in that costs a whopping $15 at the most.. hmmmm... The math was super easy in my mind..

Enjoy!

 

how about at the track , ive seemed to gain .2 seconds everytime i removed my paper air filter?

 

My issue with track testing is mainly consistancy.

While not impossible it is very difficult to reproduce exacting conditions repeatedly.

While bracket racing I can keep my times all around the same ball park but I cannot account for the difference in weather when I arrive from when the racing is at the finals.. That weather difference alone has shown me over .2 gain.

Then there are track conditions to consider..


I love racing at the track and really only count my times once they are repeatable. If I only get a fast time once, its not enough in my book to be considered valid. It has to repeat it so its not a fluke either on my part or the cars.

 

My car stock with a catback ran consistent 14.2s took off the air filter ran 14.0

with my cam although not happy with the times coulda done better i consistently ran 13.4 and without the filter 13.2 (slipping tranny bad 60s)

i only do 1 or two runs cuz i dont really feel safe running without it

the temperature and usually a 15-30 minute cool down is usually consistent to

 

I imagine that airflow characteristics with a moving car (i.e. on the track) would be different from those of a stationary car (i.e. on the dyno), even if you had a couple fans in front of the car. It's possible that when the car is moving, the fluid dynamics in the air intake system are more desireable.

Mmm, fluid dynamics...