Rev Limiters – Why Do We Use Them?

Rev Limiting – The Needle Dance…

Rev Limiters prevent your RPMs from exceeding a certain limit, which is governed by the breaking point of some part of the engine (e.g. floating a valve, breaking a rod, etc.)

Why do we need Rev Limiters? Because we don’t need any more power after a certain point, so we won’t need any more revs. More revs mean more wear and tear.

How do we set Rev Limiters in cars? Here are some of the ways:

• By a ignition cut (cutting the spark)
• By a fuel cut (turn off the injectors)
• By a throttle cut (closing the throttle)

Fuel Cut

Fuel Cut Rev Limiters are some of the most common types of Rev Limiters because they save on emissions, and increase the lifespan of emissions parts. It works by turning off the injectors past a certain RPM limit.

The risk is that when you hover around the RPM limit, you run into uneven firing, which can result in injected fuel where we don’t want it.

This type of Rev Limiter is slow, as opposed to a race Rev Limiter which notifies you with fast, rapid popping.

Spark Cut

Spark cuts notify the driver of the Rev Limit through “misfires,” where fuel is injected, but there’s no spark. It’s a good Rev Limiter in some situations, but it carries with it a major drawback: It’s really bad for emissions.

You’ll have unburnt fuel going through the system, causing emissions spikes and temperature spikes at the catalytic converter. High enough temperature results in damage. OEM cars are required to have catalytic converters that are graded to work for 100,000-150,000 miles. That’s why misfire protection is so important – they can’t afford misfires.

Throttle Cut

This type of Rev Limiter is often manually manipulated by accessing the car’s torque tables. Basically you ask for certain amounts of torque at certain levels or rev, but get less and less torque as you get closer to the Rev Limit, even at full throttle.

When you hit your Rev Limit, you ask for drastically less torque (just enough to keep the engine running).

Boost Cut

Often used as a “safety precaution” Rev Limiter, the system effects a fuel cut when you exceed a boost limit.

How To Manually Put In Rev Limiters
On ECU’s That Don’t Have Standalone Rev Limiters

Even if your ECU doesn’t support certain cuts, you can still manually institute fuel cuts, ignition cuts, ignition retard cuts, or throttle cuts as long as you can access the tables. For instance, if you can access the throttle tables, you can manually institute a throttle cut. If you can control the ignition tables, you can put in a retard ignition cut.

P.S. If you want to get more info and learn more in depth tuning strategies you can check out our Starters Edition Course by going here.

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