What happens, exactly, when you hit the redline?

[ret42]

In an auto, doesn't the rev limiter simply indicate it's time to shift to the next gear (Either automatically or manually with paddle shifters)?

Sounds simple enough. And in the last gear, obviously you need to slow the hell down if hitting the highest gear redline.

No, the automatic transmission computer tells the transmission when to shift, based on the RPM, throttle and load, and probably several other factors. I haven't had an automatic that has taken the engine to the redline without manually keeping the transmission in a lower gear.

The ONLY purpose of a rev limiter is to prevent the engine from damaging itself. Taking a stock motor to the redline is often pointless.

so if you are experiencing the engine giving out while passing, either you're a dumbass and you don't know what you're talking about or your truck is broken.

OP was referring to his Miata which is a manual, not a 4Runner.

 

[cashmoney]

I haven't had an automatic that has taken the engine to the redline without manually keeping the transmission in a lower gear.

Really? I haven't had one that hasn't taken it to redline.

 

[T4R2014]

either you're a dumbass and you don't know what you're talking about or your truck is broken.

/thread.

 

[BlackWorksInc]

If you go far enough in the Redline the ECM will tamp down the fuel injector pulse width and ignition to prevent the vehicle from reving any higher than the "max RPM" programmed in the ECM. If it is a manual and you downshift when you're max'd at the redline, well bad things can happen. We had a 2014 Scion TC that a customer bought, didn't even put 1200mi on it and was complaining of a intermittent misfire. Turns out that they over-rev'd it, downshifted and shot off about 6~7 rockers off various valves (they just fell off, didn't break anything thankfully.) To be honest we chased that for a while because at lower RPMs and cruising speeds the engine ran perfectly happy, except for a slight "miss" that everyone was like, "I dunno if I'd call that a misfire the monitor isn't even picking it up..." One of the techs popped the valve cover off and found that most every cylinder had lost almost one rocker from each set of intake and exhaust. Car breathed fine at cruising and some hard acceleration, but in the right "sweet spot" it would pop P0300's. After putting two and two together we realized what the customer did (his insistence that he wasn't "racing" was also a tip off. )

Moral of the story? Just because there is a Redline, doesn't mean you have to use it...

 

[IanB]

Correct. But over revving by downshifting or over revving by not shifting is still over revving and will still lead to the above pictures.

Over revving by not up-shifting isn't a real thing, you'll hit the redline and won't be able to rev any higher. Over revving by downshifting into too low a gear can cause some serous damage in the blink of an eye. Electronically controlled auto's won't allow this to happen, I'm not aware of any exceptions.

 

[ProspectiveBuyer]

I If it is a manual and you downshift when you're max'd at the redline, well bad things can happen.

So you're already at the redline and the next thing you do is downshift? That's a completely illogical thing to do.

We had a 2014 Scion TC that a customer bought, didn't even put 1200mi on it and was complaining of a intermittent misfire. Turns out that they over-rev'd it, downshifted and shot off about 6~7 rockers off various valves (they just fell off, didn't break anything thankfully.)

Did he admit doing that, downshifting after hitting the redline? In that case the repairs wouldnt be covered by warranty.

 

[ProspectiveBuyer]

Really? I haven't had one that hasn't taken it to redline.

Your automatic vehicle goes to redline before upshifting? Unlikely.

 

[BlackWorksInc]

So you're already at the redline and the next thing you do is downshift? That's a completely illogical thing to do.



Did he admit doing that, downshifting after hitting the redline? In that case the repairs wouldnt be covered by warranty.

Eh, I don't downshift at the redline, that was a typo...

It's supposed to echo the "downshift at the redline doesn't end well" sentiment.

Bottom Line, there's no benefit to shifting or downshifting at the redline. You want to find the power band that engine operates in and work with that. Even Rotary Engines (which LOVE higher RPMs, albeit consistent high RPMs) still don't want to be shifted in the Redlines as much as their higher powerband RPMs (there's a reason why a lot of RX7's have blown 1st & 2nd gears or blown Apex Seals and it's mainly operator error.) Redline Shifting is mainly a show-off thing, some vehicle's powerbands are very close to the redline so shifting in the "red" in some gears is forgiving, others there's no benefit from it vs. just staying under the redline in the powerband.

Movies and media make it seem like Redline Shifting is some sort of magical way to get speed, but that's more for flair than it is for anything else. Now if one where to have a built/tuned engine that is designed to rev higher than the stock RPM gauge and one is shifting in the stock Redline because the powerband is that high and the engine's real redline is higher, that's a different story (mainly that the person too lazy to properly set-up their vehicle properly.)

 

[nevada]

Your automatic vehicle goes to redline before upshifting? Unlikely.

ive driven a few that will run up to red line, if you hold it at WOT.

however, redline is not the same as hitting the rev limiter.

 

[jwkilgore]

So you're already at the redline and the next thing you do is downshift? That's a completely illogical thing to do.

Illogical, but still very possible when someone fairly new to manual transmissions tries to power-shift or speed-shift and hits the wrong slot. Trying for fourth and hitting second, for example.

Your automatic vehicle goes to redline before upshifting? Unlikely.

Quite a few of mine have gone to redline before shifting if the pedal is on the floor.

 

[cashmoney]

Your automatic vehicle goes to redline before upshifting? Unlikely.

Want a video? I can get one in my 4runner, my wife's explorer, my mom's duramax, my bil's dodge, and my sister's edge. They will all go to red line before upshifting at wot.

 

[ProspectiveBuyer]

Want a video? I can get one in my 4runner, my wife's explorer, my mom's duramax, my bil's dodge, and my sister's edge. They will all go to red line before upshifting at wot.

Sure, if you want to bother. Then, according to what people have said in this thread (at redline you're way past max. power), these shift points are not optimally programmed if you want to achieve the fastest acceleration possible. If I floor the gas the computer should take me to the gear & RPM that are optimal for acceleration, and stay there as long as the gas pedal is floored.

 

[cashmoney]

You forget that manufacturers build for the general public and the general public thinks redline is the fastest. If it shifted before then they'd complain. And my statement was merely directed at your statement of it being highly unlikely that my autos shifted at redline.

And the whole discussion around max power and redline in this thread only scratches the surface. The discussion of gearing and shift points and where they drop you back in the power band hasn't even come in to the picture yet. There's a lot more to maximizing acceleration than just shifting at max power so don't get all cocky because you read something some folks in this thread stated.

 

[1engineer]

Sure, if you want to bother. Then, according to what people have said in this thread (at redline you're way past max. power), these shift points are not optimally programmed if you want to achieve the fastest acceleration possible. If I floor the gas the computer should take me to the gear & RPM that are optimal for acceleration, and stay there as long as the gas pedal is floored.

That's an asinine statement. Read this first RevSearch Engine Dyno; Torque vs Horsepower as it is a good "101" primer to hp and torque and their relationship. If you need me to explain radians and their relationship then I will be happy to, as long as you won't argue unless you have a clue what you are talking about.

Now after reading my linked article, you should have developed a hammerlock on ignorance and understand why people say at redline you are past your max power. Most vehicles have a higher redline than 5252 rpm. As you can see your hp value will increase but your torque won't. Why? Physics and math.

Unless you are driving a race car, no vehicle will have the automatic transmission and engine programmed for the fastest acceleration. Doing this is terribly inefficient. Even with a manual transmission you are not getting there as fast as possible. Why? Because your engine's ECU is not letting your engine develop max power which of course will limit your acceleration times. Modern vehicles are optimized for efficiency, reliability and durability and not speed, with a few exceptions. Very few. But if you want to get confrontational and call people out when they are only trying to help then you will get no help at all from anyone.

Read the article before responding.

Edit: got Torque and HP backwards.

 

[ProspectiveBuyer]

double post

 

[ProspectiveBuyer]

That's an asinine statement. Read this first RevSearch Engine Dyno; Torque vs Horsepower as it is a good "101" primer to hp and torque and their relationship.

I appreciate you trying to help. I've read that article, which does little else but define torque & power.

As you can see your torque value will increase but your hp won't. Why? Physics and math.

Hmm.... The link you provided goes at great lengths to establish that
power = constant x torque x rpm ( where the numerical value of the constant depends on the system of units you use ).

Therefore, if your torque increases as a function of RPM, power must increase too. What "physics and math" am I missing, exactly?

Unless you are driving a race car, no vehicle will have the automatic transmission and engine programmed for the fastest acceleration

that's reasonable

 

[cfranck1]

There's a lot more to maximizing acceleration than just shifting at max power so don't get all cocky because you read something some folks in this thread stated.

I read it on the internets, so it must be true!!

 

[ret42]

Really? I haven't had one that hasn't taken it to redline.

I'll try the 4Runner and see if it takes me there. I've only had a couple of automatics, mostly manuals.

Hmm.... The link you provided goes at great lengths to establish that
power = constant x torque x rpm ( where the numerical value of the constant depends on the system of units you use ).

Therefore, if your torque increases as a function of RPM, power must increase too. What "physics and math" am I missing, exactly?

Might want to double check that formula, chief.

 

[1engineer]

I appreciate you trying to help. I've read that article, which does little else but define torque & power.



Hmm.... The link you provided goes at great lengths to establish that
power = constant x torque x rpm ( where the numerical value of the constant depends on the system of units you use ).

Therefore, if your torque increases as a function of RPM, power must increase too. What "physics and math" am I missing, exactly?



that's reasonable

I am trying to show you the relationship between torque and hp. Below 5252 rpm you will always have more torque. Above 5252 you will have more hp.

You didn't get the formula right even after you read it.
Here it is written long hand:

HP=((torque)(rpm))/5252

The constant 5252 comes from dividing 33,000 by 2pi radians. This constant is used when dealing with torque using "lb-ft" units. Maybe it's easier if I manipulate the formula for you:

TORQUE=((HP)(5252))/RPM
You can clearly see how this proves other poster's point of running out of torque as you approach 5252 rpm.

This is why 5252 is a more important RPM to use than "redline" rpm.

 

[ProspectiveBuyer]

I am trying to show you the relationship between torque and hp. Below 5252 rpm you will always have more torque. Above 5252 you will have more hp.

Sorry, that's just plain silly. So above 5252 rpm the numerical value of power (expressed in some system of units) exceeds the numerical value of torque. How is that important?

You didn't get the formula right even after you read it.
Here it is written long hand:

HP=((torque)(rpm))/5252

Speaking of understanding formulas, you wrote:

As you can see your torque value will increase but your hp won't.

Mathematical impossibility. If torque increases with rpm, i.e. both factors on the right hand side increase, then their product (HP) will also increase. If both x & y increase, x*y will also increase, to put it simply. Dont get distracted by (1/5252).

Now, if RPMs increase and torque decreases, then HP may go up or down, depending on how much RPMs increase vs how much torque decreases.