What happens, exactly, when you hit the redline?

[ProspectiveBuyer]

I have a manual Miata, and when I accelerate hard in 3rd (usually on an on-ramp), I can easily get to the redline. The moment I hit the redline the car stops accelerating, as if I took my foot off the gas (even though I don't). Is it the computer cutting off the gas, or is it a sudden drop in engine power output once RPMs get too high?

BTW, what's the point of a tachometer in a vehicle with automatic transmission?

 

[cashmoney]

You can manually shift an auto. And it's called a rev limiter. It cuts power, spark, fuel, etc to keep people from over revving their engines and blowing them up. It's on all vehicles these days. There are also speed limiters that do the same but based on speed instead of rpm.

 

[ProspectiveBuyer]

You can manually shift an auto. And it's called a rev limiter. It cuts power, spark, fuel, etc to keep people from over revving their engines and blowing them up. It's on all vehicles these days. There are also speed limiters that do the same but based on speed instead of rpm.

Thanks. I suspected it was the damn computer. Wonder if there is a way to disable it.

 

[02SE]

Thanks. I suspected it was the damn computer. Wonder if there is a way to disable it.

Of course there are ways to disable and/or raise it. The question is why do you want to?

Also, if you don't know how a rev-limiter works, I would suggest that you might not want to disable or raise it. Because all you're likely to achieve, is an engine damaged from revving beyond the RPM the stock component(s) can handle.

Yes, rev-limiters can be raised, but engine parts will need to be changed, to parts that can handle the increase in stress.

Also, if the engine lacks sufficient airflow through the engine (due to restrictive head ports, cams, valves, etc, etc) to make more power at higher RPM, then a higher rev-limit is a waste of time anyway.

 

[ProspectiveBuyer]

Of course there are ways to disable and/or raise it. The question is why do you want to? .

Because it is dangerous to have an electronic nanny suddenly, unexpectedly, cut off the gas when, say, I am trying to pass or merge.

Your other points are valid.

 

[hearno]

BTW, what's the point of a tachometer in a vehicle with automatic transmission?

It's a gauge like any other on your dash...

 

[ProspectiveBuyer]

It's a gauge like any other on your dash...

But it doesnt convey any "actionable" info...

 

[hearno]

But it doesnt convey any "actionable" info...

Like when to upshift when in sport mode? Also, I like to know where my RPMs are at. Regardless of the type of transmission in my car.

 

[CookieRoe]

I think all you need to know is when you hit redline;

BAD THINGS HAPPEN

so stay out of it.







Ok good night y'all

 

[ProspectiveBuyer]

Like when to upshift when in sport mode? Also, I like to know where my RPMs are at. Regardless of the type of transmission in my car.

My wife has one of these shiftable automatics. The fact is that is that it doesn't always obey you, the computer will always take over. You dont really have control over the RPMs.

 

[hearno]

My wife has one of these shiftable automatics. The fact is that is that it doesn't always obey you, the computer will always take over. You dont really have control over the RPMs.

Ok... You asked a question and got an answer. The point of the gauge is to monitor rpms... Like the temp gauge allows you to monitor coolant temp. No one said it gives you control over rpms.

 

[2014 Warthog]

My wife has one of these shiftable automatics. The fact is that is that it doesn't always obey you, the computer will always take over. You dont really have control over the RPMs.

That is somewhat true at the low end but in S-Mode you can rev WAY higher than the ECT would allow when in normal mode. If you want to offroad well or accelerate hard from a stand still or for passing, S Mode gives you a lot more control over the RPMS than without it (Even if it isn't absolute)

 

[cashmoney]

Because it is dangerous to have an electronic nanny suddenly, unexpectedly, cut off the gas when, say, I am trying to pass or merge.

Your other points are valid.

Or learn to drive and shift before you hit red line? You do know you aren't supposed to hit the redline and then sit on it right? It's there so you don't take an engine designed not to go past 6000rpm (or whatever your car is set for) and take it to 7000 or higher and blow it up.

 

[BrianSD_42]

Because it is dangerous to have an electronic nanny suddenly, unexpectedly, cut off the gas when, say, I am trying to pass or merge.

Your other points are valid.

Are you for real?

Like he said LEARN TO SHIFT LIKE A NORMAL ADULT DRIVER.

Suggested reading for anyone needing a refresher or yuppies who never even had auto shop in HS:
http://auto.howstuffworks.com/transmission.htm

.

 

[ret42]

Because it is dangerous to have an electronic nanny suddenly, unexpectedly, cut off the gas when, say, I am trying to pass or merge.

Your other points are valid.

Shift? Odds are extremely high that if you're bringing the engine to the rev limiter in a stock vehicle, you've already exceeded peak torque and horsepower, so acceleration and especially speed are being hindered by the gear you're in, not by the redline/rev limiter.

Your driving is the danger here, not the electronic nanny that has been around for the past 30+ years.

But it doesnt convey any "actionable" info...

Sure it does. Maybe you're drag racing an automatic and need to know when you've hit peak power to manually shift. Maybe you're hauling a trailer and going down a steep grade, and to save the brakes you want to downshift a gear (or two). Automatics haven't always had tachs. They've become more and more common because car manufacturers realized that people find the information useful for various reasons.

 

[IanB]

Because it is dangerous to have an electronic nanny suddenly, unexpectedly, cut off the gas when, say, I am trying to pass or merge.

Your other points are valid.

If you have a tach, it's not really unexpected where the redline/rev limiter is, is it? You just weren't paying attention. Passing or merging safely requires being in the right gear for the situation, and may even require a shift mid maneuver.

Your auto trans not obeying your commands if it means damaging the engine is probably a good thing if it's interfering in your driving on a regular basis.

 

[KidVermicious]

Because it is dangerous to have an electronic nanny suddenly, unexpectedly, cut off the gas when, say, I am trying to pass or merge.

Your other points are valid.

This is utter bullshit, how did you type this with a straight face? There is absolutely no need ever to bounce off the rev limiter at any point in a daily commute, and it can't take you by surprise anyway because there's a BRIGHT RED LINE ON THE TACH.

Save it for the racetrack, Andretti.

 

[amalik]

Maybe you're hauling a trailer and going down a steep grade, and to save the brakes you want to downshift a gear (or two). Automatics haven't always had tachs. They've become more and more common because car manufacturers realized that people find the information useful for various reasons.

Hi-jacking the thread here for a second, I think the OP got plenty of answers.

So basically on a steep downhill, it's better to be in a low gear and no foot on the break at all in an automatic? Or a combo of the low gear and the break pedal?

I understand the scenario and how to do that (i.e. shift into 1 or 2, O/D off, etc), but wouldn't that put strain on the lower gears considering they can't upshift to the next gear i.e. and the downhill/gravity force of the slope trying to make the car go faster?

 

[Quatre Coureur]

Maybe change your user name to 'DestructiveDriver'... :lookout:

 

[cashmoney]

Hi-jacking the thread here for a second, I think the OP got plenty of answers.

So basically on a steep downhill, it's better to be in a low gear and no foot on the break at all in an automatic? Or a combo of the low gear and the break pedal?

I understand the scenario and how to do that (i.e. shift into 1 or 2, O/D off, etc), but wouldn't that put strain on the lower gears considering they can't upshift to the next gear i.e. and the downhill/gravity force of the slope trying to make the car go faster?

No because what you are doing is using a combination of gearing and engine braking and service brakes to slow the vehicle down instead of relying solely on the service brakes. By downshifting you are keeping the RPM's up higher and taking advantage of the engines natural braking. There's no or little strain on the transmission doing this. You are also keeping the torque converter locked up which also helps slow things down which also helps keep the transmission fluid cooler.