Interesting Rb25 Neo Miss/pop After Intake Install

[Shoujiki]

Ok guys, don't shoot me for trying this, it was just for "fun" because I had it sitting around and wanted to have a play in the garage!

Engine normally runs perfectly, smooth idle, no issues.

Now I installed this "drift" pod filter, removed the airbox etc. All neat and installed correctly. Car runs awesome and is of course wooshy and noisy haha.

However, when returning to idle when warm, the engine has a miss. It pops and the rpms drop (you can see the needle bouncing). Not by alot, but certainly feel it through the car. After 5 or so seconds, it's fairly constant again.

Put the airbox back in (which has an Apexi high flow panel filter in it) and no miss, runs smooth as again.

What is the pod/open filter doing that's causing it to miss like that at idle? It it actually getting more air, causing an issue with the tune? I didn't think the stock airbox was that restrictive. It was a very cold day here in Melbourne, and the under bonnet temp was fairly cool (not heat soaking). Would a "better brand" filter of these types work better? I notice lots of cars run apexi of hks filters, this drift one I got with the car (first thing I took off) so wonder if it's of poor quality. Weirdly, engine runs great when driving with it!

Thanks, Kurt

[GTSBoy]

It's changing the relationship between the amount of air actually flowing through the AFM and the air velocity at the location of the flow sensor in the middle of the AFM. The entry conditions into the AFM from the stock airbox are X and the entry conditions from the pod are Y. The entry conditions are different. Put the pod on, and because it is symmetric around the centreline, maybe it flows slightly more air on average through the AFM than it does with the airbox on....but at the exact same velocity on the centreline where the sensor is. Hence you get leaner operation than you do with the airbox (assuming it is leaner of course. If it's actually richer, then the opposite would have happened).

[Shoujiki]

Gotcha, thanks GTSBoy for explaining it like that, makes sense. It's a fairly cheapy filter, i wonder if having like an Apexi power intake would make it different again. As i said it's on at idle, when driving it feels fine.

How do other get away with having these things on? Live with the misfire/poppy idle? Or re-tune to adjust for it? I had an NA car before this and changing between open and airbox filters would make no difference in perceivable engine operation.

[GTSBoy]

Assuming it's running leaner, it'll feel fine and fast under load and at revs. Leaner is more powerful. But of course that might be lean enough to be dangerous, so you have to keep that in mind.

Some people have no idea that the change in the car's running is associated with the last mod they made (the pod) and so just either live with it or don't even notice it. Assuming you have a tuneable ECU, it is trivial to tune it out.

Whatever your last car was (assuming not a Skyline) - obviously the effect of changing the filter was not as severe. Every single type of car will have a different response. Just depends on the unique shapes involved.

[Dose Pipe Sutututu]

The Apexi pod is ok, doesn't seem to disrupt the AFM that much, however sometimes I did notice a dip on the revs if you've been cruising then go to a stop.

But stock airbox is always the best, first thing I did when I got my 2nd R33 was put the stock airbox back on