During full throttle up changes I quite often get a muffled pop which is apparently accompanied by a small puff of sooty smoke.

Having searched it seems quite a common thing with scoobs.

I understand the pop is down to unburnt fuel igniting in a hot exhaust, just not the soot..?

Car is running extremely well and goes like ****..

05 WRX (340x333)
full decat 2.5"
ported headers
VF35
pink inj
walbro
Green panel
Sti TMIC/scoop & undertray
PRF7b's
ecutek
v-power + millers OB
etc, etc..

I'm not worried in the slightest by this, just curious..

BTW running oem recirc. DV. and not using any oil..

 

the magnex decatted zost i have just had fitted pops a lot when car is warm... quite like it !

 

Your car is running rich, it means the petrol never burns completely and will always leave soot. Just the way petrol burns unfortunately.