I've tried several different intakes to test them out on my 04 WRX. These include, Blitz LM short ram, GP moto short ram, Blitz SUS, HKS short ram, Greddy short ram, and now APS 65mm intake. It seems that with all of them, If I'm at low RPM's in 5th gear and accelerate(slightly bogging the car), then release the gas, then quickly hit it again, the car will slightly buck and I hear a hollow pop sound. It only happens sometimes if I do it under those conditions, otherwise it runs fine. Anyone else experience this?

 

I had this bucking problem when i installed the aem cai.. it seemed to buck when i was cruising at low speeds and would step on it.. i ended up taking the intake off and puting my stock airbox back on.. no more buck and car seems to accelerate much smoother..

 

Cobb had the question answered about intakes and their tuning software. I thought this was informative:

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Q. I have XYZ intake, do you have a map for it?

A. We can do mapping for quite a few intakes that are predictable. We have maps for the original(black) APS, Injen, and most of the short ram hot air intakes. The Blitz is about the only short ram that is not predictable. The car may not be as smooth or might miss out on some power since we have to tune even more conservatively with most of the intakes, but it will be safe, and run better than the factory ECU. Also, let us know what specific intake you have. We have had people order the map for the APS intake when in reality they had other intakes. Needless to say the tune was far from optimal. So far the AEM is about the only intake we have seen that is not predictable. We could make a map for it that would make sure that the car runs rich rather than lean, but the benefits would be far less than that if the customer just removed the intake and used the factory unit. We even have to do that on the dyno for the AEM intake. Also, even if the intake is advertised as not needing correction, causing no errors, or factory specifications, let us know. This is not the case on the intakes that we have tuned that make this claim, they do require correction. Just because the piping that the sensor sits in is the exact factory spec does not mean that there is no turbulence to throw the sensor off. In the end if you want the smoothest running car use the factory air box. If you want the noise and slightly better spool-up, remove the silencer in the fenderwell and toss a panel filter in the stock air-box. On the stock turbo you will make the same power as you will with an aftermarket intake. If you have any questions or want to get the best map, your best bet is to give us the most information you can and let us choose the proper map for your combo.

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From here:
http://cobbtuning.com/forester/accessport-faq.html

 

It's just good practice that if you install an intake, get your car tuned for it.

 

I've read all the FAQ's and archived posts about intakes on Subaru's already and the APS 65mm supposedly doesn't cause as much MAF reading fluctuations as other intakes. This has been tested by people who have datalogged with the intake on. Still I can't find out what is causing the hollow pop noise from the intake area. Anyone know what it could be?

 

Could it be a backfire through the intake tract? If so would this cause any damage?