When you lift off the throttle with the car in gear some cars have it and some cars don't. I assume it's inefficient and undesirable from the factory but I like it and since the CSPish Miata doesn't get DD use anyway why not make the car more smile inducing.
How is that effect achieved and other than being fun for car-dorks is there any reason you wouldn't want some crackle-pop.
For this specific case it's a '97 answer with RB CAI, JR header, FM cat/exhaust. What do I need to change/add/modify?
Cars with cats will crackle less than cars without cats. Usually crackle is a function of the throttle being pretty far closed, ignition timing being retarded at closed throttle and not being in decel fuel cut. If the ECU doesn't retard the timing at closed throttle and/or goes into fuel cut very quickly when you're not at low rpm, it won't crackle noticeably without re-tuning the ECU.
Its basically a rich fuel condition under deceleration. Much more common with carbureted engines for the reasons rslifkin mentioned.
'90 with RB Header, enthuza metal core cat, borla no-resonator catback. It occasionally crackles and pops when throttle lift-off timing works out just right. As they said, make it run rich and get the cat off of there. Not legal, maybe not worth it, I don't suggest you do it, but I think that could be your answer.
My Scoob used to do that. I agree, very enjoyable.
It's about time for me to start throwing $ at that POS so I can thrash on it once more.
Cat delete isn't required to get some crackle, you'll just get more without it. And if the cat isn't tucked up tight to the manifold / header, it'll have less of an impact on crackle.
Even when my car had no cat, plus a header and full exhaust, it never really did it. I always figured it had to do with the fairly mild compression ratio and conservative timing.
My MINI does it with a cat back system. It's even better sounding if you put light pressure on the throttle pedal going down hill.
Exhaust crackling can actually be good for emissions...better to burn off the fuel than let it go unburned. However it would've been more efficient to burn it in the cylinder, or in the cat. Still, better than releasing unburned fuel.
The only downside is that sometimes you can get a huge explosion that can damage your exhaust - a mechanic I used to work with tried intentionally tuning a car to let off huge explosions on overrun, at the owner's request, and the exhaust inflated to an egg shape after a while.
Corsa Sport mufflers did it for my Corvette. They sound excellent.
bravenrace wrote: Its basically a rich fuel condition under deceleration. Much more common with carbureted engines for the reasons rslifkin mentioned.
we pulled the choke.
Fuel injected cars cut the fuel on closed-throttle decel. That's why you don't hear it much anymore, and why cracking the throttle on a MINI can bring it back. Carbs aren't that smart.
Mis-adjusting the TPS could potentially bring it back. Basically, you don't the ECU to know the throttle is fully closed. I'm not sure if the 1997 uses the TPS or the separate idle switch to trigger the cutoff, but it might be worth disconnecting the idle switch to see. It's one of the four wires on the TPS plug, see wiring diagram for details.
If you have a programmable ECU, you may be able to turn off the decel fuel cut which leads to fun pop and crackle. Even flames if you have a short, catless exhaust on your Locost 
Playing with the DFCO setting on a GM PCM can give you a nice stereo crackle out of the dual exhausts on an LS3 conversion - makes me laugh like a little kid.
On the Jeep, I ended up gaining some crackle in the quest for better engine braking. At closed throttle, it retards the timing significantly. So at lower rpm, it crackles pretty steadily at closed throttle. At higher rpm, you'll get a little crackle and sometimes a pop or 2 when you back off the throttle for the first second or 2 before fuel cut engages (delay is around 2.5 seconds to keep it from jumping in/out of fuel cut too easily).
My rx7 does it.... A lot! Fireballs FTMFW....
My Saab 900 has a little bit of this too. I think part of the exhaust is loose, don't know for sure yet.
I noticed it when it got warm enough to roll the window down. It gave me a big smile.
wvumtnbkr wrote: My rx7 does it.... A lot! Fireballs FTMFW....
Abarth does the crackle-boom stock.....sometimes you can even hear 2 distinct booms as it lights both rear exhaust tips at a different interval.
It doesn't always do it, but quick upshifts can also yield a pop as well. Decel is when I get rewarded with fire. 
Turbo cars tend to do it a bit more since they tend to run a little more rich from the factory and many cars would use the throttle bypass solution to add some air into the combustion chamber.
Chrysler turbos do it quite a bit when their exhaust is opened up (like the SRT-4/500 Abarth)
Sometimes bad things happen. Saw this on Solomatters FB page this morning.
my 2013 Mustang does it big time. No cats and a axel back plus a tune that mimics a big cam at idle.
Rusnak_322 wrote: my 2013 Mustang does it big time. No cats and a axel back plus a tune that mimics a big cam at idle.
A tune that mimics a big cam? Like you get the sound of a lopey cam from playing with the mixtures? That sounds like it just wastes fuel and you don't get the power of actually having cams. Weird.
crankwalk wrote:Rusnak_322 wrote: my 2013 Mustang does it big time. No cats and a axel back plus a tune that mimics a big cam at idle.A tune that mimics a big cam? Like you get the sound of a lopey cam from playing with the mixtures? That sounds like it just wastes fuel and you don't get the power of actually having cams. Weird.
On a DOHC V8 with VVT, they just screw with the cam phasing to create a ton of overlap at idle like a big cam would have, which makes it choppy (and does waste some fuel).
It is called a "ghost cam". Does nothing for performance, but the car rocks back and forth at idle like a Harley. Thought it was kinda stupid, but the guy that did my tune gave me one with and one without the fake cam and to be honest, I love it.
BTW: Ford is offering it with their track key, so you can get it and keep your warrantee. Not sure how they got it to work without killing the CATS as that was a big thing with all the aftermarket tuners.
My 1965 Lotus 7 does it, and with flames out the left side of the car right bext to me. Super short exhaust system, Weber carbs rich at idle, not much of a muffler and no Cat. The clamps where it goes from 2 tubes to 1 leak a bit, and that helps too, I'm sure.
It gets old on the road. I've only owned it 29 years, and I'm thinking I should do something about it.
El Rabbitto gives some brap brap on decel due to big primaries, no cat, and big exhaust. Still trying to find a better tone as it's a shade ricey despite a magnaflow oval...
Buddy's JCW mini pop's all the damn time. Funny thing was he tended to drive with the windows up and always playing music so never noticed that much. We got in it down at VIR to drive from our camp site to the paddock with a few others sitting in the open hatch. When it started popping, he was really confused then happy it was his car, had never realized it sounded so good. I've got a miata so would be interested to hear if you can get any car to do that w/out compromising anything.
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