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Old 04-02-03, 10:01 PM   #1 (permalink)
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Redline vs. Rev. Limit

It's nothing too big, but i have noticed it is thought the two terms of Rev Limit and Redline are interchangeable. First, yes, the two terms refer to engine speeds in relation to high speeds. Also they do sometimes tend to reside in the same RPM bracket but the two are not the same.

First lets look at Redline. Redline is the term used to describe the rpm range in which the engine is enters into a "danger" zone according to a Marketing and manufacturing agreement. this zone is sometimes well below an engine's true "Redzone". A Redzone in relation to a Tachometer is the area in which the guage ceases to be diffident to engine speeds, normally marked by a LARGE Red band Hench the term RedZone. The point at which the guage no longer sees engine speed with unbias (or where it turns red) is called "Redline".
here is an example:

Please disregard my wanton capturing of Initial D shots (also the fact that the guage is all REDlol)
THIS shot shows the REDZONE from ~7500-9000rpm the actual Redline is the beginning of this Zone which would be 7500rpm.

Some high performance manufacturers of the past used to also implement Yellow zones. You will notice that Ferrari, Porsche, Lancia, and even alot of non european highperformance cars had Yellowzones. These zones really are here to extend warning to a driver that the "Redline" is comming up or if the engine is cold that this new extended area should be taken into regard. they dont really serve much purpose beyond that.
an Example of a yellow zone(im sorry if you cant see it...look all the way to the right. The area from 7000-7500 rpm is a YellowZone)

notice the Yellow after after 7000rpm and it quickly changes to red at 7500rpm. 7500rpm would be the "Redline"

Now for the actual Rev Limit. a rev limit, as you might or might not know, stops an engine from revving any faster. The most antiquated and still very effective way of limiting engine speed is stopping Ignition spark to the cylinders immediately which in turn halts the engine acceleration, it feels like fuel is being taken from the engine so hotrodders coined the phrase "Fuel Cut". The MOST disadvantageous aspect of this method it its ABRUPT halt in engine operation for a split second which really can be felt and heard and if not timed correctly when it lets spark come back, can cause detonation. Our cars have a "Soft" limiter which first retards timing a little, then more then cuts the ignition power (within a few milliseconds) this causes more of a surging feelin rather than a series of whiplash inducing jolts. Still another method used is the Throttle control method. Cars with Electronic throttles (in some cases) use the computer to close the throttle when it reaches its Rev Limit and this in turn creates another type of soft revlimiter.

Now for practicle application. Dinan/Bayou Stage II roms, increase fuel delivery and also raise the...REV LIMIT. Rev limit as stated before is where the engine will cease to accelerate to high speeds. Redline is the Manufacturer's stated starting point of the "unsafe for daily use" area of a street driven engine. So Redline and Revlimit, though reside in the same area of engine operation, are not the same and in most cases cannot be interchangeable.

one

Last edited by B+O; 04-02-03 at 11:52 PM.
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Old 04-02-03, 10:57 PM   #2 (permalink)
 
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good info
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Old 04-03-03, 12:56 AM   #3 (permalink)
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That's awesome to know. What's the TypeIIs "Fuel CutOff"

6700rpm? What does the StageII bayou raise it to?
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Old 04-03-03, 11:43 AM   #4 (permalink)
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so i can put my car in nutral or park and floor it and the RPM needle will bounce up and down at the top of the redline area like it does on grand turismo whne your holding the button before the race???? im to scared to do this im sure its not good for your car but i kinda wanna do it once for kickes.
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Old 04-03-03, 12:15 PM   #5 (permalink)
 
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Quote:
Originally posted by FutureX 2001
That's awesome to know. What's the TypeIIs "Fuel CutOff"

6700rpm? What does the StageII bayou raise it to?
I want to say 7200, I have taken it up to 7000 in third w/o hitting the Rev Limit.
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Old 04-03-03, 12:22 PM   #6 (permalink)
 
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Originally posted by LegendC


I want to say 7200, I have taken it up to 7000 in third w/o hitting the Rev Limit.
I've had it past 7200 on my tach, but I think it's just an error at this point. PPP says the rev limit is raised to 7200
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Old 04-03-03, 12:26 PM   #7 (permalink)
 
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Could be, do remember that the Tach gets thrown off a bit from true engine speed at uppper RPM's, just like the speedometer at high speed..
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Old 04-03-03, 03:34 PM   #8 (permalink)
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Already knew all that, but great writeup!!!
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Old 04-04-03, 03:13 AM   #9 (permalink)
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I'm guessing stock TypeII is 6900rpm limit/fuel cut off. I saw it bounce off 6900rpm today before it shifted into 4th.
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Old 04-06-03, 11:25 PM   #10 (permalink)
 
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Originally posted by Roger
so i can put my car in nutral or park and floor it and the RPM needle will bounce up and down at the top of the redline area like it does on grand turismo whne your holding the button before the race???? im to scared to do this im sure its not good for your car but i kinda wanna do it once for kickes.
Sure you can
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Old 04-30-03, 02:01 AM   #11 (permalink)
 
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The car redline or engine danger zone is there to protect the vehicles motor from valve float and oil starvation at those high speeds pluss with would you rev the engine up to 7K RPMs if the max HP is at 6K?? Just like my 2.0 16V VW motor with 150HP with max at 6200 RPMs but has a 7K redline and fuel cutoff at 7.5K and I rev it max at 6.5K only in first gear and drop a few 100 RPMs for the next shift.
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Old 04-14-06, 01:08 PM   #12 (permalink)
 
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Originally Posted by Bang&Olufsen DK
Now for the actual Rev Limit. A rev limit, as you might or might not know, stops an engine from revving any faster. The most antiquated and still very effective way of limiting engine speed is stopping Ignition spark to the cylinders ...
Sorry to revive this but just HAD to comment. The truly most antiquated rev-limiter was a broken connecting rod. Bad juju.

Next, if you were lucky, was valve float. The valve springs couldn't keep up with the cam profile and valve weight at higher rpm. Very effective, let me tell you. Granted, this was not an intentional rpm limiter, but worked just the same. This was fine on low-compression engines, but on high-compression engines, valve float typically led to bent valves.

With the advent of electronic fuel injection, spark and fuel cuts became available. Spark cut was the first limiter tried, and it works pretty good and is easy to implement, but as B&O mentioned, it has problems, including flooding the catalytic converter with raw gasoline. More bad juju. So, the more sophisticated engines use fuel cuts, sometimes progressively cutting cylinders as needed to return to "safe" rpm.

No rev limiter will protect your engine if you shift into a gear that will mechanically drive the crankshaft beyond rev-limit rpm, like being at redline in third gear and reaching for fourth but grabbing second instead.
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Old 05-15-06, 07:24 PM   #13 (permalink)
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hmmm, I'm just curious as to why mine hit 7,600 RPMs before it cut out. It's only a Type I Auto.
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Old 05-22-06, 04:45 PM   #14 (permalink)
 
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Your tachometer is dead accurate? The tach in my Sentra reads 500 rpm fast at redline.
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Old 05-22-06, 05:00 PM   #15 (permalink)
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Originally Posted by slartibartfast
Your tachometer is dead accurate? The tach in my Sentra reads 500 rpm fast at redline.
Actually that is the reading with a digital Tack. 7,620 RPMs is where mine cut's out!
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