Since I installed My SLPs, I notice is is louder the first minute after starting cold. Then it seems to get quieter. Is this something the computer does at start-up? Or do the cats get quieter when warm?

 

This should happen even when stock. It's the engine itself which runs very different when cold. It will also start and almost rev to higher rpm's right away then quite down if thats what you are reffering too.

 

The compy adjusts the timing so that additonal heat is expelled into the exhaust to get the cats up tp light off temperature faster, if you start the car dead cold and then sit around the tail pipes and listen to the exhaust you can hear it change timing after reaching whatever predetermined operating temp it needs to get at for the timing to change back to normal.

 

bob, that's interesting, I never knew that the car was trying to get the cats up to the right temperature when you first start it. You learn something new every day.

 

Yeah, the faster you can get the cats to light off, the faster you can reduce cold start emmisions, When I put my SLP X-pipe and Loud Mouths on my old 02 it was really pronounced if you laid into the throttle when it was cold, sounded like crap but as soon as the car warmed up it changed for the better.

 

The exhaust also changes tone as it gets up to temperature and sounds different(at least with chambered mufflers) when warm.

 

It seems to me its alot like choking the engine on a dirtbike... When the engine is choked the engines RPMs stay up higher until the choke is turned off... Our cars just have an automatic choke.