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 RED
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.