Im on an rb downpipe and presilencer with stock mufflers. Rest of engine all stock.

When i rev high enough or shift high in the rpm range it backfires significantly and a puff of smoke comes out. Is this just unburnt fuel? Normal?

 

What color is the smoke, if it blue its oil, prob the oil control ring are starting to go, under deceleration at high rev the engine under high vacuum and oil is suck in through the ring and burn off.

 

Nope its just white and dissipates pretty quickly

 

Is the white smoke thick?

 

Relatively. Its not like a huge cloud

 

If your coolant level is OK, and if you live in a colder climate area, its prob unburn fuel, rich afr, my car smokes in cold start till its warm up, catless exhaust

 

Well my car is doing it under high revs when at full operating temp. And its not all that cold here in socal.

 

Some more info about the car would help.

 

79k original miles. Compression is very good. All stock besides cat deletes

 

More? Significant differences between S4&5

 

And it is an s5

 

Just out of curiosity, and lack of knowledge, what are the oil control rings and what magnitude of repair is required when they do go out? Rebuild time?? Minor fix?

 

oil control rings are located on the side of the rotors, oil pass through the eccentric shaft and lubricate the rotor bearing, the ring prevent the oil from going into the chamber.
when oil control ring goes, engine oil seeps into the combustion chamber and the oil is burn off, smell of burning oil and blue smoke out the exhaust.
to replace oil control rings, require a rebuild. rotary or piston engines.

 

But it never smoke at all before i deleted the cats so idk

 

You say it white smoke, and your coolant level OK, I think its just unburn fuel

 

Are the pops and smoke between shifts only? If yes probably un burnt fuel igniting in the exhaust. I would ask if you got flames at night but with stock mufflers they don't make it out of them due to the chambering inside.

Oil control rings getting worn tend to smoke on startup but then clear up once things get warmed up and begin to seal. But yes a rebuild is required to replace them but if compression is good and it's not smoking constantly I wouldn't touch them. That said I don't think it is the oil control rings anyway.

 

Yes only between shifts or high revving. And no smoke on startup except on the coldest mornings (which are only like 30s here)