Is it bad to hit the rev limiter?
31 January 2002, 12:21 PM
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I was over taking on a dual carriage way today and was in third with the music blasted - suddenly felt the gas go dead, then realised I was in the red - I've done this a few times - is this bad for the car or can they handle this?
31 January 2002, 12:23 PM
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Dont worry too much about it, the car is designed to take a little more than that (see how they test engines and you wont have a problem hitting the red line!!) the one thing it does is cut your boost so you dont over do the turbo, its best if you change up before the redline thou!
Tony
Tony
31 January 2002, 01:07 PM
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Pat Foster wrote a piece on scoobynet a while ago about why hitting the rev limiter in a turbo'd car is a Bad Thing(tm). Something about sending the turbo supersonic.
Unfortunately the search is down so I can't find it.
Whip
Unfortunately the search is down so I can't find it.
Whip
31 January 2002, 01:09 PM
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Nooooooooo don't do it!!!
On a friends car with a mappable ECU (Wulf) we set the limiter at 8000rpm and still saw rpm figures in excess of 9 grand
Obviously once or twice isn't gonna be a problem but I wouldn't make a habit of it!
Bob
On a friends car with a mappable ECU (Wulf) we set the limiter at 8000rpm and still saw rpm figures in excess of 9 grand
Obviously once or twice isn't gonna be a problem but I wouldn't make a habit of it!
Bob
31 January 2002, 01:22 PM
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Rev limiter - might as well be called the incompetence limiter 
It's there as a safety back-up (e.g. if it pops out of 5th gear on you ) - it's not there as a target. It's been very noticeable that many of the cars that have had the engines go bang have been driven by people who rev the car up to the limiter, particularly on the track.
Myself, I can't understand why people do it anyway.
The power and torque collapse above about 6500rpm (UK car) anyway, and you're running low boost by that point, so you'll get faster acceleration by changing up a gear anyway. Pointless to run to the 7400rpm limiter.
And yes, it does do damage doing it repeatedly - the rate of engine wear is massively higher at the top end of the scale. Otherwise why wouldn't they red line at the limiter? Or raise the limiter?
There was a thread a while back about someone in a Jap-spec WRX whose rev-limiter failed, and he didn't spot this until nearly 9000 rpm (how on earth?? [img]images/smilies/mad.gif[/img] ). The engine let go not long afterwards. Say no more.
Make up your own minds but I've never been one to rely on it as a back-up for being able to change up by the sound of the engine.
Richard
It's there as a safety back-up (e.g. if it pops out of 5th gear on you ) - it's not there as a target. It's been very noticeable that many of the cars that have had the engines go bang have been driven by people who rev the car up to the limiter, particularly on the track.Myself, I can't understand why people do it anyway.
The power and torque collapse above about 6500rpm (UK car) anyway, and you're running low boost by that point, so you'll get faster acceleration by changing up a gear anyway. Pointless to run to the 7400rpm limiter.And yes, it does do damage doing it repeatedly - the rate of engine wear is massively higher at the top end of the scale. Otherwise why wouldn't they red line at the limiter? Or raise the limiter?
There was a thread a while back about someone in a Jap-spec WRX whose rev-limiter failed, and he didn't spot this until nearly 9000 rpm (how on earth??
[img]images/smilies/mad.gif[/img] ). The engine let go not long afterwards. Say no more.Make up your own minds but I've never been one to rely on it as a back-up for being able to change up by the sound of the engine.
Richard
31 January 2002, 01:58 PM
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To Quote Pat (hope you don't mind Pat) from "that thread" back on the old BBS:
Anyone wants to read the rest of Pat's post (there's quite a bit of it), you can find it here.
So, don't do it, you have been warned...
Matt
[Edited by mutant_matt - 1/31/2002 1:59:41 PM]
Rev limiters are a Bad Thing (TM), they are about as mechanically sympathetic as a nuclear bomb.... no matter what strategy is used, on a turbocharged car they won't do your engine any favours at all.... keep away from them. The fact that most people with KnockLinks observe a BIG RED when hitting the limit should be warning enough!
To just expan a little on the subject, a limiter must rob the engine of torque. There are two ways that this can be done....
1) get rif of fuel or
2) get rid of the spark... you could do both of course.
Option 2) is VERY VERY dangerous on a turbocharged engine, IMVHO. If the spark is removed, then for the first few cycles, fuelmix will just get blown through the exngine.... this will then light up in the very hot manifold. At this point, even if you has a wastegate the size of a dustbin it would be unlikely to prevent the turbo from overspooling.... you're effectively shoving the best part of one megawatt of heat energy into it.... pooor little thing. So you have NO boost control... so the boost builds relentlessly and all of a sudden even though you have no spark, fuelmix lights up in the cylinders in a very detty way. Not good for rods or bearings!
The alterantive is to cut fuel. This is a bit kinder, but also risky. The injectors wet the manifold when running. So if you shut them down there will still be fuel, so for one or two cycles the cylinder will run pretty lean, before it shuts down good and proper. Conversely when the injector is fired up again it will have to wet the manifold again, so the first few cycles will be lean unless the ECU can extend the first pulse (a wetting-pulse.... some advanced ECUs can do this). But it's still not ideal...
Rev limiters are there to stop the engine machanically flying apart due to over-rev, they are NOT there for use as a shift indicator, OK?
To just expan a little on the subject, a limiter must rob the engine of torque. There are two ways that this can be done....
1) get rif of fuel or
2) get rid of the spark... you could do both of course.
Option 2) is VERY VERY dangerous on a turbocharged engine, IMVHO. If the spark is removed, then for the first few cycles, fuelmix will just get blown through the exngine.... this will then light up in the very hot manifold. At this point, even if you has a wastegate the size of a dustbin it would be unlikely to prevent the turbo from overspooling.... you're effectively shoving the best part of one megawatt of heat energy into it.... pooor little thing. So you have NO boost control... so the boost builds relentlessly and all of a sudden even though you have no spark, fuelmix lights up in the cylinders in a very detty way. Not good for rods or bearings!
The alterantive is to cut fuel. This is a bit kinder, but also risky. The injectors wet the manifold when running. So if you shut them down there will still be fuel, so for one or two cycles the cylinder will run pretty lean, before it shuts down good and proper. Conversely when the injector is fired up again it will have to wet the manifold again, so the first few cycles will be lean unless the ECU can extend the first pulse (a wetting-pulse.... some advanced ECUs can do this). But it's still not ideal...
Rev limiters are there to stop the engine machanically flying apart due to over-rev, they are NOT there for use as a shift indicator, OK?
So, don't do it, you have been warned...
Matt
[Edited by mutant_matt - 1/31/2002 1:59:41 PM]
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