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Redline vs. Rev. Limit
I thought I would repost this excellent explanation from Acura-Legend.com explaining the difference between red line and rev limit on Honda's. The demand on an engines internals goes up exponentially as the rpms rise. People who remove the engines soft limiter and /or fuel cut off are making the call that the increase in performance is worth a shorter engine life.With even the most recently built Prelude engines approaching 10 years in age,removing the engine restrictions above 7.4k rpm is becoming a increasingly more potentially expensive proposition.
Red line vs. Rev. Limit
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It's nothing too big, but i have noticed it is thought the two terms of Rev Limit and Red line 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 Red line. Red line 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 "Red zone". A Red zone in relation to a Tachometer is the area in which the gage ceases to be diffident to engine speeds, normally marked by a LARGE Red band Hench the term Red Zone. The point at which the gage no longer sees engine speed with unbias (or where it turns red) is called "Red line".
here is an example:
Please disregard my wanton capturing of Initial D shots (also the fact that the gage is all REDlol)
THIS shot shows the RED ZONE from ~7500-9000rpm the actual Red line 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 a lot of non European high performance cars had Yellow zones. These zones really are here to extend warning to a driver that the "Red line" is coming up or if the engine is cold that this new extended area should be taken into regard. they don't 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 Yellow Zone)
notice the Yellow after after 7000rpm and it quickly changes to red at 7500rpm. 7500rpm would be the "Red line"
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 feeling 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 rev limiter.
Now for practical 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. Red line is the Manufacturer's stated starting point of the "unsafe for daily use" area of a street driven engine. So Red line and Rev limit, though reside in the same area of engine operation, are not the same and in most cases cannot be interchangeable.
one
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Last edited by B+O; 04-02-03 at 11:52 PM.
Last edited by SH DRIVER; 07-08-2010 at 09:56 AM.
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