Start up bark

[GlynMo]

Hi,
How do Mazda (and others) produce the 30 second-ish exhaust 'bark' on start up, and is there a way to make it permanent???

[GlynMo]

Mr-B said:

Are you talking about the higher idle speed after a cold start like it's on choke? (ha ha anyone remember chokes? Ask yer dad) If so I think it's and emissions thing to make the cats warm quicker.

Yes, I am, but the sound on cold start up is also noisier, which I like! It sounds as though there is a valve on the exhaust that opens on cold start but closes when tickover temperature is reached, but it does all seem to be to do with emissions and cat heating, although I don't see how this makes the sound louder and more aggressive.

(I'm well acquainted with chokes, having been a driver for 50+ years!!)

[GlynMo]

Mr-B said:

Dunno if there is a valve in the exhaust. Next time you start it have a look to see where the revs are held and once they die down rev it back up to the same point and see if the sound is the same.

Good idea, why didn't I think of that?! On cold start, revs are held at 1500rpm and the exhaust sounds throaty. After 30 seconds or so, revs drop to idle and the sound is more subdued, and remains subdued on revving back to 1500rpm. It looks like a standard back box, with no sign of a valve.

So, I'm as befuddled as before!