Probably a dumb question

Computer programming is causing it. They literally designed the flatulence into the fuel mapping to sound "cool." My 991 had this "feature" (one of the reasons I sold it). It's completely made-up. I've been driving carbureted cars my whole life and none of them do that.

 

People tune modern cars to do that they call it ‘pops and bangs’. Sounds so artificial and not well running for sure.

 

Properly set up Carburated cars won’t sputter. I am also not a huge fan of this as well as the built-in rev matching cars have now. Yes, I perhaps sound like not a race car driver, but so be it in my eyes. Leaves room for improvement.

 

Cam timing, high valve lift, long cam duration with lots of overlap, and un-burnt fuel igniting in the exhaust headers.
Its a typical by product of many race engines, not specific to carbs, I feel some manufacturers program it into the fuel map so people feel like they're driving a race car.
There is some benefit as the un-burnt fuel does help to cool things down on overrun among other things........
So whilst its a simple by product of a proper race engine, some buffoons want to have this happen in their road cars for the "cool factor".

 

I'm also curious why some 355 even spit out fire? I've reved mine quite a few times at night, there's definitely no fire that comes out the back.
I suppose if you had a leaky injector, maybe that would happen.

 

In a modern engine it is definitely done for the "cool factor", and doesn't increase performance. Carbureted engines had a bit of that, I would call it more of a "burble" on run down, rather than popping and banging. The popping and banging that happens is usually done in an turbocharged race engine (think WRC) and some very racey turbocharged road cars (F40), where fuel is intentionally dumped and ignited in the exhaust during rev-down in order to keep the turbo speed high to avoid a lag during the next acceleration. Often called bang-bang or anti-lag. I don't think even the wildest amount of valve overlap in a naturally aspirated engine would legitimately cause a "bang" of that magnitude, unless done solely for effect. It seems to me that some of the newer vehicles are almost trying to mimic this anti-turbolag "coolness", even if the engine is not turbocharged....
An F355 does occasionally pop when shifting at the redline, and I would be lying if I said that wasn't cool

 

Mine spat out fire on redline up shifts with cat less Y Pipe. Not so much with OEM Y Pipe.

 

Looking forward to premature catalytic converter failure, anyone?

 

I will say, our cars have an awesome rumble when cruising around 3,000 RPM or so, in gear If you just slightly tap the gas. One of my favorite things about it

 

I think it really is the best sounding engines of all time, not only for the high rpm shriek, but the idle sounds amazing (almost like a 2 stroke engine), and in the dense urban area when going slow (3200rpm is 2nd gear for example) the hollow horn / oboe type noise echoing off the buildings is just fantastic. And to the point of the thread the legitimate "pop" on a high rpm shift is icing on the cake.

 

I’ve also driven carbureted cars my whole life, and EVERY one of them has done that on hard deceleration, especially in the cold.

 

My '77 308 only popped in the cold on hard deceleration.

 

My ‘68 Javelin, 65 ‘Fastback, ‘70 Chevelle, ‘68 Fastback, both Factory Five Cobras, ‘66 Corvette and ‘85 C10 all did it. Perhaps not all the time, but definitely when decelerating in the cold and definitely if I was just coasting down a hill.

 

I forgot to mention in my post, its even easier to make it happen in a newer engine as almost all new engines have variable camshaft timing, so this can be adjusted by the ECU to maximize and have a nice flat torque curve all the way through the rev range. You can also program it to have massive amounts of overlap for extra scavenging effect and so on and so forth.
This with a few extra squirts of fuel can ignite and produce nice big ass flames out your exhaust system, especially with no cats........
My completely stock Euro 348 flames out the exhaust and has some nice cackles with the straight pipe, no cat exhaust.....

 

my Alfa GTV with weber carbs "burbles" on decel (sounds great by the way). If it goes "bang" that is a sign that it is too lean (as others mentioned - happens when the engine is cold)

 

My 360 does it a little when cold on overrun (decelerating) with my foot off the go pedal.
My '83 Mondial (not carburettor) used to do it all the time but a low deep popping. I though it did sound cool.
New cars as mentioned have it programmed in and do it way too often and to me sound false.

Bikes still do it I think.

 

the recipe for blue flames for my 355 was straight through pipes and an el-cheapo unbranded exhaust box. I had blue flames out of the tail-pipes from about 6,500 RPM to red line.

Anyway, I took all that stuff off and currently run a totally stock factory exhaust system (due to draconian noise regs where I now live).

No flames, not as glorious sound but on the plus side, it doesn’t stink.