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Airbox testing

Bruce Nunnally

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While I have the May GM HTP mag open, also want to mention that they tested 7 different custom airboxes on a 2000 Z28, both on the dyno and at the track. They seem to have followed a very reasonable methodology for testing -- even going to the relative extreme of using a 'locked down' PCM to avoid PCM learning from test to test.

The stock airbox made 314, 319, and 321 hp on three pulls.

The best dyno replacement lid made 331, 330, and 330 hp on three pulls.

The stock best quarter was 13.12s at 108.6 mph corrected for atm.

The best track replacement lid did 12.92s at 110.05 mph corrected.

I know, 1 mph in the quarter does not SEEM significant, but it does equate to about a 10 hp change.

In summary then, just changing the airbox yielded about 10 hp on this mostly stock LS1. Why didn't the factory build the camaro airbox lid that if it was just that simple -- these aftermarket lids are $89-149 retail, so say

On a related topic, I was reading a similar review in a tuner mag where they tested a variety of intakes, and did a nice summary. They tested each intake 3 times on a dyno, and published the best time for each. Massive test time.

One of the intake suppliers was upset with the result -- they did not win the comparo -- so they duplicated the test with the mag's example car. The supplier got the same results they had been getting in their own tests -- that their intake was superior. So what was the problem? The magazine and the supplier used slightly different tests. The supplier tested on the dyno with hood up, to simulate cooler air flowing in like when the car is moving. The mag tested on the dyno with the hood down. The supplier used an average of 3 runs. The mag used the best of 3. Different results, same parts. Moral of the story, it just depends on who is telling the story sometimes. In this case both parties were right, but under different conditions.

But also in that case, all the custom intakes outperformed the stock intake. Also in that test, a drop-in panel filter did no or negative gains.


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I'd agree that the stock airbox (and exhaust) is designed to meet a lot of requirements other than max air flow. The biggest is probably noise. If you want to cut noise, you can't have a big resonating box. You need to baffle and stream line the flow up to and away from the filter. I think the best example of this is the air box on the 3800. Very little of the filter area is actually used and the fresh air is literally chanelled right up to the filter face and also leaves the box in the same fasion. This isn't the best for utilizing the filter area but sure cuts down on sound resonations in the box. Just guessing here but the stock air box probably does as well as some superior flowing design up to a pretty high rpm - probably over 4000. So, for most driving situations, you aren't losing anything anyway. But if you want every bit of power possible at WOT to redline and think a growling intake sounds cool anyway (I do) then go for it. To be really safe you could always have your oil analyzed to make sure some aftermarket box is indeed sealing correctly and not leaking anything on you.

As for the other intakes and testing with the hood up or down - I assume this is concerning the exposed cone type intake. If so, the hood up or down will make a huge difference as these things will suck hot air off the engine. Personally, I think they do the same in regular driving situations too. The heated intake air can really kill power.

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I agree with Guru that many after market products are the result of "hindsight" and "massaging", but if you are aware of the consequences (ie: water intrusion, growling intake,which I also like,etc) then there is nothing wrong with that after market product if in fact it does produce more power. Ironically it does seem to depend on each individual car as to how well that after market product performs.

In my case the K&N cone filter set up is much better than stock which I have proven with track results. I have modified it so it is completely heat shielded and ducted down under to draw fresh air. Even though many on this board say it made there car worse.

Same with the exhaust. You can get more power but the trade off is louder. If it doesn't bother you then go for it. I love the sound of my Corsa exhaust, but that's me.

There are always compromises.



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[The only thing bad about a big volume air box is the outside of it resonating from the induction pulses inside and creating a noise of it's own.]

Yeah - that's what I was talking about.

However, if you look at the air box on any 3800, the volume of the box was NOT utilized - especially on the intake side. The fresh air is literally "piped" up to the filter face. Maybe I'm wrong, but it sure seems that the volume of the box is deliberately separated from the flow.

Support ribs or not, I'd still expect a large air box to resonate like the body of an accoustic instrument - like a guitar. In fact a guitar is heavily braced inside and it of course resonates to make a lot of sound.

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I took the resonators out of my box and the intake duct tract in part because while the intake resonance buzz might have been quieted instead i had to put up with several friends making jokes about when would the tea be ready and put the plug back into the bathtub! Under heavy acceleration I would get a loud sound that sounded like water boiling in a tea pot. A Seville I test drove did the same thing as did another Aurora out of the 1/2 dozen Caddys and Auroras I test drove before buying my salvage car and partially rebuilding it.

The three years is up so I could go down to the dmv and get salvage removed from the title now if i was so inclined.

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