‘Crackle maps’, ‘Pop and bang maps’, call them what you will, they’re mega popular. But are they safe and should you get one? Fast Car investigates…

Pops, bangs and flames; everyone likes that, don’t they? Well, hell yes you do, and because of this, ECU remaps that make your exhaust pop, bang, and kick flames from the tailpipe when you lift off the throttle are hugely popular these days.

But how do they work? And, more to the point, are they bad for your engine’s health? Well, unless you’ve been living in a cave for the last few years, we’re sure you’ve heard loads of comments both good and bad; it’s time for a Fast Car investigation into the matter, so we can find out the truth for you guys.

As this is a bit of a controversial subject in the tuning scene at the moment, a lot of companies, understandably, declined to get involved. But thankfully, the guys at Motorsport Developments are experts when it comes to remapping all factory ECUs, and were more than happy to give us their words of wisdom and help confirm our findings on this subject – so a huge thanks to them. They’re certainly the guys to speak to if you want a safe, but effective map yourself!

Pop and bang maps

What are pop and bang maps?

The exhausts of heavily-tuned cars have naturally popped, banged and flamed since the dawn of time, but have you noticed lately, a lot more cars than ever before have been popping and banging from the exhaust when the driver lets off the gas? Mildly-tuned motors and even quite a few factory production cars now have a cool burbling exhaust on the overrun.

This is because lots of tuners and manufacturers have realised that owners love these kinds of noises. And with modern engine management being so damn capable, it means that they are now commonly mapped into the car’s ECU tune.

How does it make the pop and bangs?

For this bit, let’s start with the expert words of main man Stewart Sanderson from Motorsport Developments…

“Pops and bang maps, or burbles as the OEM call it (yes, it’s that common on production cars that even the manufacturers have a name for it!), is simply a calibration feature within the ECU where we set up a specifically targeted, very lean misfire once you lift off the throttle.”

Normally on an engine when you close the throttle, your fuel injectors don’t fire at all, removing all energy from your engine, allowing it to slow down: this is smooth, quiet, and safe, acting and sounding like all the sensible ‘normal’ cars we’re used to. No pops, no flames, no nothing.

Back to Stu’s words of wisdom… “If we want to create a burbling sound while the engine slows down, we need fuel. But, burning fuel will create some piston load too, slowing the rate the engine will decelerate on the overrun – so we need to move the energy away somehow to prevent that,” he explains. “To do this we need to do two things: retard the ignition timing to reducing the torque which allows the car to decelerate normally, and run a very lean air/fuel ratio so too much heat isn’t created, which could affect reliability.”

The heavily retarded ignition also means much of the combustion happens with the exhaust valves open (in fact within the exhaust system), and much of the fuel is ignited by the hot exhaust and/or catalytic converter, hence the burbles, pops and crackles you hear from your tailpipe.

“The intensity of the burbles on these set-ups varies depending on the exhaust temperature – how hard the car’s been used. The hotter the exhaust system is, the easier this tiny amount of fuel we add flashes off,” Stu explains.

But what if you don’t want subtle OEM-style burbles and fancy something crazier? Well, the methods are similar to the above, but with a little more fuel added and even more ignition retard. We’ve even seen people go so far as opening the idle speed control valve or opening the drive-by-wire throttle a little for more air too. In fact, these modifications (albeit with more extreme settings and for more than just a few seconds at a time), are actually the basis of how anti-lag systems work on rally cars. But this isn’t a performance mod, this is purely to create cool noises and flames!

Pop and bang maps

Can crackle maps be applied to any engine? 

In a word, no. But it can be done to a hell of a lot more engines today than ever before. In theory, it can be done to any petrol engine – normally aspirated, supercharged, or turbocharged – anything that has an ECU with which the fuel and ignition settings can be heavily modified, which these days means most of them.

Some cars can have their ignition retarded further still, and allow the ability to open the idle valve or open the throttle a little, all of which can provide more extreme pops and bangs, if that’s what you want. So, providing you can find a tuner capable of adjusting your ECU to suit, the vast majority of engines can have this applied to some extent at least.

Do pop and bang maps have any performance advantage? 

No. This is done purely for the noises. As it works in a similar manor to rally anti-lag systems, really extreme set-ups could, in theory, work like a mild anti-lag system on a turbocharged engine, helping keep your turbo up to speed. But in reality, the pops, bangs and burbles usually happen only for a few seconds after you let-off the gas, and it’s done purely for the sound. If you were able to set it to such an extreme level that it had a true anti-lag function, you’d be calling it anti-lag, not a crackle map!

Are pop and bang maps safe? Do they damage your engine?

This is by far the most controversial part of this subject, and while the answer is sometimes yes, providing your map has been done by someone who knows what they’re doing, it’s highly unlikely to cause any real issues. Any potential reliability issues will come from the same thing that gave performance remapping (or chipping as it was known a decade or two ago) a bad reputation – people doing it badly.

OEMs have ECU tunes that include ‘burbles’ that are reliable and designed to last 100,000+ miles of hard use. Reliability issues stem from a remap (be it for pure performance or for pops and bangs) being done in an unsafe manner – too extreme for what the engine can handle, and therefore doing damage.

“We offer more extreme versions of the pops and burbles, but because this requires adding more fuel, you can only have it with a catalyst-free exhaust. There is only so much fuel you can burn off before you poison the catalyst. If it smells of sulphur, it’s dying,” says Stu.

More than just the cat can be damaged, though, if the pops and bangs remap is too extreme for what your engine can handle. Extreme heat from richer mixtures and heavily retarded ignitions can cause extreme exhaust gas temperatures, which even with a de-cat could possibly damage lambda sensors, exhaust systems, and potentially more.

But, what are the chances of actual engine internal damage with one of these maps? Well, if you look at the internet, every man and his pet monkey has a story about a friend of a friend whose uncle has damaged an engine due to this. In reality, we’ve yet to find a single case where engine internal damage was definitely proven to be caused by the pops and bangs mapped in to the ECU.

Certain engines have relatively weak exhaust valves – Renault F4Rs, for example, and these maps have been blamed for damaging them quite a few times. But hard used versions of these engines often end up with the same valve damage, regardless of the map, so it’s still speculation rather than proof.

Again, speaking to the guys at Motorsport Developments, Kenny has seen cars come in to their shop with quite extreme ‘crackle map’ tunes done elsewhere, with 30-degrees of ignition retard and quite rich fuelling. This is verging on the settings you’d use on an anti-lag system, albeit only happening for a few seconds at a time on a map like this. This certainly isn’t something they’d recommend on a typical engine, and would cause really high EGTs during the ‘crackle’ period. It, therefore, has more potential for damage to be caused. But still, they’ve never personally seen engine internals damaged from this.

pop and bang maps crackle cars exhaust

Should you get a pop and bang map?

Some people love pop and bang maps, while others hate them as they feel they create ‘fake’ noise. But if you want one, there’s no reason to believe your engine will be destroyed If you do things correctly. There’s still a lot of debate about this, but try as we might, we’ve seen no proof at all.

This is the important bit though – you need to ensure you have the right set-up for your engine. Do you have a cat, or an engine with a known weak point in the exhaust system or exhaust valves? If so, you’d be advised to keep it to a sensible, almost OEM-style burble, rather than full-on WW3 in your exhaust.

But regardless of your set-up, choose your tuner wisely. Find someone who will ensure it’s reliable and safe for your particular set-up and chosen use. Pops and bangs are fun, but an engine that isn’t broken is even more fun, so don’t just go for someone who promises the craziest, loudest fireworks display from your exhaust – that’s just asking for trouble.

Thanks to: Motorport Developments for all of the info and advice.

Words: Stav