A rev limiter takes care of your engine, even if you get carried away with having fun. For instance, if you’re on a track with your sports car, blasting through the gears, and at one point you overshoot it - If you have a rev limiter, things won’t be bad, but if you don’t, you’re looking at a busted engine.

Remember the old Need For Speed Most Wanted? Unlike everything else car-related, they actually demonstrated this experience quite accurately in the video game. During the race, you’re supposed to change gears yourself. If you tried to achieve the ‘perfect shift’ and waited too long, the engine revs too high, and you hear a clank followed by the words "blown engine".

This happens when you over-rev and don’t change gears at the right time. For just this reason, manufacturers install a rev limiter to protect the engine against damaging itself. This is the fundamental reason why you can’t go past the redline in your car.

Updated April 2022: A two-step is a secondary rev limiter that holds a certain RPM for optimum power delivery, which is now popularly known as launch control. Unless the setup is wired to increase pressure inside the exhaust manifold, two-step rev limiters are generally not bad for your engine. You can also now get many after-market kits for it.

How Do Two-Step Rev Limiters Actually Work?

What does 2 step rev limiter do
Via VolcsnoRacing

As the name suggests, a two-step rev limiter locks the revs at two points: one being the conventional redline and the other, where your car thinks is best for a better launch, or to deliver optimum power. Commonly found in modern-day sports cars, it can be either had as an OEM part or as an aftermarket mod.

Your engine doesn’t have to be redlining for a perfect launch, as that’d be wasteful since you’ll end up having unnecessary wheel spin. There is a sweet spot in the engine’s rev band where you get the most amount of effective torque, and that’s where the first limiter is set. The moment the car is launched, there is no further role for the first limiter.

Generally, there are two ways you can employ rev limiting; fuel adjustment and ignition control. Fuel adjustment is what most OEM manufacturers go for because of emissions and safety concerns. In this setup, supplying the engine with a lean air/fuel mixture, or even shutting off the fuel supply, would help with limiting the revs.

Supra shooting flames 2 stepping, anti-lag, two-step
Via: a98malcolm

In an aftermarket setup, however, things are rather different. For starters, instead of fuel, the ignition is cut off completely, which results in no power produced. That said, this leads to a significant amount of unburnt fuel getting inside the exhaust manifold, leading to the infamous pops and bangs we might hear from a sports car's exhaust note.

Another commonly used method is retarded timing. IN This case, the ignition happens midway during the power stroke, which leads to unburnt fuel entering the exhaust while keeping the effective work done at a minimum. Not an ideal solution concerning efficiency, nonetheless.

Along with this, heavily retarding ignition is also a common practice. Here, the mixture is ignited at the end of the power stroke, and this results in partial ignition occurring while the mixture exits through the exhaust valve. Now, here’s where a question arises: isn’t this anti-lag? Well, it functions similarly, but, it’s not.

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How Does Two-Step Rev Limiter Differ From Anti-lag

What is antilag
Via: VisioRacer

Anti-lag is something that works very similar to aftermarket two-stepping limiters but varies significantly. Anti-lag is a system that keeps the turbos spooled when you’re off the throttle. A two-step limiter can be seen in both naturally aspirated or turbocharged engines, whereas anti-lag is only found in turbocharged units.

Ever seen a rally car's exhaust popping and banging? That’s anti-lag. Fundamentally, turbos have an inherent issue by design, which is called turbo-lag. This happens because of the time it takes to build enough boost. As boost is directly related to exhaust pressure, it's important to keep it optimum at all times for maximum performance.

Pressure build-up is nearly impossible without throttle inputs, and in order to get that sorted, anti-lag systems are employed. The engine runs a rich air/fuel mixture when you are off the throttle, which after combustion enters the exhaust manifold. Next, the air is supplied externally, which ignites the mixture inside the turbo, thereby creating boost pressure. This spools up the turbo and eliminates lag when you get back on the throttle.

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The Potential Downsides Of Two-Step Rev Limiters

a blown engine result from overrevving
Via: cashcarsbuyer

As mentioned earlier, they are generally not bad, but it largely depends on what sort of setup you have installed. If it’s an OEM unit, you can be rest assured it’s going to be robust since a lot of endurance tests are conducted to make it reliable. Furthermore, the setup employed is a lot safer on the engine and helps with emissions.

On the contrary, aftermarket units tend to favor ignition cuts that supply unburnt fuel to the exhaust manifold. The pops and bangs are enticing, but the stresses in play are something to be worried about. OEM exhaust manifolds are not designed to handle such amounts of stress and could result in serious engine damage. In fact, you could potentially end up with a blown manifold in no time. So, you need to be careful.

Sources: wikipedia.org, drivetribe.com, youtube.com