Rev Limiter Question

[Dak2Zeke]

Today while driving around, I put the car in S mode and forgot i had it in S and forgo to shift and redlined it in first gear. Can this do any damage? How exactly does the rev limiter work? Nothing strange happened and i didn't hear a sound, so just curious if this can do damage to the engine and how the limiter works.

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[smann]

You're okay don't worry!

Hitting the rev limiter happens sometimes. You didn't do any damage to your car. Power is cut to the engine and it prevents you from doing any damage to your engine when you try to push it.

Don't drive your car constantly in the higher RPM's, it can cause premature wear and tear.

But nothing to worry about.

 

[DoubleX]

As I found out this weekend, the car will cut power once you hit redline. I'm happy the car is smarter than I am, but man, do I wish the car had a shift lift or something.

 

[Mustang1260]

Your fine so do not worry - you would be very aware of damage by now.

Is a rev limiter a perfect idiot proof device- no. The engine computer will record such events and Ford will pull those electrical records if a serious warranty claim is made (they will deny a claim based upon owner abuse).

A good buddy replaced his engine (suv, on his dime) a few yrs back when he exceeded the normal rpm range. Downshifted an auto to make a boneheaded pass, rev limiter kicked in but he still over-reved the engine and 80 miles later the slight tick noice that developed post pass became a knock followed by a rod pretty much destroying a cylinder wall.

In over 40 yrs and millions of miles of driving (all kinds of sticks to autos) I've hit redline or a rev limiter maybe 6 times. I've never seen a forum like this one where folks think hitting redline is a cool thing (hey cool the display goes Red--really, I wanna try that...or they admit to how many times they hit redline as if it was a badge of honor instead of the badge of stupidity that it is)....not saying the OP said that and one time mistakes do happen (hell I've done it about 6 times but over 40 years on a manual) but the number of threads and posts therein is staggering on this topic.

 

[Mustang1260]

As I found out this weekend, the car will cut power once you hit redline. I'm happy the car is smarter than I am, but man, do I wish the car had a shift lift or something.

It doesn't cut power..it is a fuel cutoff---the car cuts off the flow of gas in an attempt to save the engine.

 

[My_Coyote]

I guess having an automatic is idiot proof

 

[Gurjit]

don't worry about it, ford sells warranty approved supercharger and performance packs which increase rev limit to over 7k and make up to 727hp

you hitting the limiter on a stock engine wont do anything

 

[Blacktop]

It doesn't cut power..it is a fuel cutoff---the car cuts off the flow of gas in an attempt to save the engine.

Are you sure it cuts fuel?

I will never understand why ford would pull fuel at redline rather than pull spark. Pulling fuel at a critical rpm would make it run instantly lean. I've read that pulling spark is safer.

 

[GT Pony]

As I found out this weekend, the car will cut power once you hit redline. I'm happy the car is smarter than I am, but man, do I wish the car had a shift lift or something.

The tachometer backlight turns red just before hitting redline ... might only be on the premium models.

 

[TomcatDriver]

Are you sure it cuts fuel?

I will never understand why ford would pull fuel at redline rather than pull spark. Pulling fuel at a critical rpm would make it run instantly lean. I've read that pulling spark is safer.

I think it cuts spark, which will be instantaneous. Cutting fuel with port injection would result in a very small but finite delay.

 

[Eritas]

This is why we need auto shop back in highschool.

It's fine and designed to prevent damage when accelerating. Mis-shifts and mechanically over-revving engines can and will damage your engine, but purely accelerating and forgetting to shift and bouncing off the rev-limiter won't damage anything. Running your engine at high RPM is fine as well.

 

[NoVaGT]

These engines can safely be revved well past 7K RPM, it won't hurt anything. The engines just don't make any power, so you might as well shift.

 

[Freedom]

redline is absolutely safe stock on an auto. Think of it this way, Ford performance tunes take it to 7500 redline with warranty

 

[DickR]

I think it cuts spark, which will be instantaneous. Cutting fuel with port injection would result in a very small but finite delay.

What I think happens is that the drive by wire system simply closes the throttle as needed to keep the revs at or slightly below the rev limit even though the throttle pedal is floored.

This is based on OBD rpm and throttle position data from a Race Technology DL1 data acquisition system installed in my 2015 GT PP used for autocrossing.

The example shows the throttle at 100 percent until the rev limiter (about 6800 rpm in second gear) is reached. Then even though the rpm stays at or near 6800 rpm the throttle closes significantly even though I kept the pedal to the floor until needing to brake for a tight corner. Note that acceleration was already dropping at the point where I put the vertical line. That is why longitudinal g's at that point were so low.

EDIT (again if anybody is reading this "real time" as I do Ninja edits):

I just remembered that my dealer who is an SCCA road racer found "the calibrator" for these engines who provided the following information:

There is a soft limiter at 6850. It backs off the throttle blade.

There is a hard limiter at 7k. At 7k it shuts off the injectors.

As soon as it goes below 6850 you get full throttle back.

This info came directly from the calibrator as there is no lag/recovery time.

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[HeelToeHero]

Your fine so do not worry - you would be very aware of damage by now.

Is a rev limiter a perfect idiot proof device- no. The engine computer will record such events and Ford will pull those electrical records if a serious warranty claim is made (they will deny a claim based upon owner abuse).

A good buddy replaced his engine (suv, on his dime) a few yrs back when he exceeded the normal rpm range. Downshifted an auto to make a boneheaded pass, rev limiter kicked in but he still over-reved the engine and 80 miles later the slight tick noice that developed post pass became a knock followed by a rod pretty much destroying a cylinder wall.

In over 40 yrs and millions of miles of driving (all kinds of sticks to autos) I've hit redline or a rev limiter maybe 6 times. I've never seen a forum like this one where folks think hitting redline is a cool thing (hey cool the display goes Red--really, I wanna try that...or they admit to how many times they hit redline as if it was a badge of honor instead of the badge of stupidity that it is)....not saying the OP said that and one time mistakes do happen (hell I've done it about 6 times but over 40 years on a manual) but the number of threads and posts therein is staggering on this topic.

You're misinformed...

Also Redline and rev limiter are different. Shifting at the Redline is the optimal shift point for maximum performance (generally speaking). If you've only done this 6 times...you're missing out.

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