Discussion
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!!)
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!
It may be just a physics thing, pushing hot air initially through as system that is cold and then through metal that has warmed through slightly may produce a different tone. Maybe you need a brass musician to tell us if this is a thing or not 
The make up of the exhaust gasses probably changes too as it comes "off choke". Could be a number of variables at play.
The make up of the exhaust gasses probably changes too as it comes "off choke". Could be a number of variables at play.There's nothing changing in the exhaust system.
It's part of the rapid warm up procedure and is done to quickly bring the manifold pre-cat up to temperature (that's what it's for and why it's put so close to the engine), the fuelling and timing is modified for that purpose.
All cars do if but it's particularly prevalent with the "skyactiv technology' ND cars - my partners Mazda3 with the same 2. 0 engine does and sounds exactly the same as the ND MX-5.
It's part of the rapid warm up procedure and is done to quickly bring the manifold pre-cat up to temperature (that's what it's for and why it's put so close to the engine), the fuelling and timing is modified for that purpose.
All cars do if but it's particularly prevalent with the "skyactiv technology' ND cars - my partners Mazda3 with the same 2. 0 engine does and sounds exactly the same as the ND MX-5.
GlynMo said:
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???
I'd like to know if you can turn it off, and also disable the program that makes my ND start with a blipped throttle. The MX 5 engine makes an anodyne blare at best and I don't want or need the 'varoom' when I start it up in Tescos... How do Mazda (and others) produce the 30 second-ish exhaust 'bark' on start up, and is there a way to make it permanent???
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