To redline or not to redline? (RPM)

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Lets get this out of the way..... I am not looking for thoughts on oil for low rev vs high rev engines.

I am upon (possibly) my first E30 or E46 Bimmer purchase which brings this debate with myself to the surface. This topic has come up many times in the past with me, mostly when discussing turbo cars (yes I understand that we must run close to the line in a turbo car) but Im talking in general.
The reason this came up in the BMW discussion is becasue the census on there forums is that some of the reliability issues that plague some Bimmers is because people drive them like a commuter car rather then a performance car.... Most feel that to keep a BMW in tip top shape you need to drive it in a "spirited" manor as much as possible. And we have all heard the old saying of "I gotta blow the carbon out"


In a nutshell:
Generally speaking is it better in the long run to nail redline or run higher RPM then it is to try and baby a motor? By baby a motor I do not mean lug the motor I mean keeping very low revs and shifting WELL BEFORE redline.
In other words is better to "put around" at lower but safe RPM or is better to have a "spirited" driving style within reason?

As always folks, thanks for playing along! I look forward to the upcoming discussion.
 
Redline under load is fine, but don't redline in neutral. The engine is designed to operate to the redline, if it is in good condition there can be no harm done with the action. Good for cleaning out carbon and making your spine tingle!
 
Pretty much what KGMtech posted. Avoid the "high vac" revs like downshifting from 5th to 2nd and dropping the clutch at 50mph. Lots of difference in rod loading from WOT RPM to the same RPM with no load.
 
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My e46 (5 spd manual) runs about 4krpm at 80-85.

I dont have any real info to add, just letting you know for your possible purchase.

Mines for sale if you want to come to ga for it
smile.gif
 
I suspect that this is nonsense.
While almost any engine seems to run better after the occasional hard run through a few gears, constant operation at high revs will cause higher wear and it matters not whether the engine was made by BMW or Chevrolet.
Driving gently except for those times where it's necessary or desirable to run the engine hard will prolong its life.
Running hard for grins now and then is fun and perfectly fine, but I wouldn't consider it either necessary or desirable to keep the revs up at all times in typical driving.
More BMW engines are probably ruined by owners using the wrong oil on long drain intervals than by being babied.
 
They USED to say you had to rev the bleep out of Porsche engines "because they had roller bearing cranks which didn't get lube unless you revved them" . The overhaul garages loved it.
 
There's no "blowing the carbon out" in modern cars. There's nothing to blow out. Any improvements from doing full throttle runs would be from the ECU learning, possibly putting in a little more timing or getting a little more aggressive with shift points.msometimes performance cars or their owners use a cold plug that can (unlikely) foul from easy driving and this might be "blowing the carbon out" though it's really just burning off a light ultra thin layer from the plugs. I would love to know what they're saying about how running it hard can help reliability.

Good advice to not rev it near redline without a load on it. It's more likely to throw a rod on the exhaust stroke without a load on it. Most newer cars are limited to a lower rpm in neutral vs in gear. I think my Acura is limited to 4.5k in neutral and 6,900 in drive. I haven't tried out the other cars.
 
Originally Posted By: AcuraTL
There's no "blowing the carbon out" in modern cars. There's nothing to blow out
Really nothing to blow out?
 
Babied engines tend to burn oil at higher rpms or highway runs. Lots of people interpret this as a sign that high revs are not good.
High revs, it doesn't have to be red line, WOT and some compression braking every once in a while are a very good thing, plus it's fun to use all the ponies that were paid for.
 
If your car is subject to mostly highway use, there is no need to do any form of Italian tune up.

Short term redlining is not going to help burn out Carbon deposits from the cylinders or exhaust system, what you need is steady highish RPM at or below the max continous RPM listed in the owners manual. That can be done by driving in 4th instead of 5th if you have a mechanical gearbox.

It's also worth using a can of injection system cleaner to make sure the injectors don't gum up if you use cheap fuel, as bad injectors can cause carbon deposits.

Preheating systems that reduce the engine warm up time in winter are also a good idea and can reduce carbon deposits a lot. Many high time engines that get short tripped a lot ultimately fail from worn valve guides and rings. A lot of that wear is caused by combustion byproducts, mostly carbon, rather than poor lubrication.
 
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Speaking strictly post-break-in--

Consider the analogy offered by sport bikes (600 & 1000cc supersports or 'race homologation' bikes, like the Honda CBR600RR, etc). My former CBR600, for example (a carbureted MY2000 CBR600F4), offered 110hp out of 0.599 liters, it redlined at almost twice most car engines do, and it ran down the highway at >4k rpm at 60. That series of CBR will very easily run 100,000 miles on the shared-sump engine and tranny, if you can somehow prevent the owner from crashing it. There are even a couple running around with over 200,000 miles on them. You just change the oil and filter (Honda calls for 8k mile changes) on time and keep rolling.

Now, is that bike being 'exercised' on any public roads on this continent? Good grief, no. Occasional full-throttle blasts up an on-ramp, or perhaps a track day here and there, certainly, but in general street use qualifies as babying such a motorcycle. Using them that way, they last very nearly forever.

Will they last that long if they're used 100% in road racing? Frankly, I'm not sure anyone has ever tried or been able to road-race one that long, but I also know of no one anywhere who has taken one that far with exclusively road-racing miles.

I don't know whether this helps you think about your question or not. Clearly a BMW car is simultaneously much lower-performance and differently-engineered than a Japanese supersport motorcycle. Still, I can't help but think there's a useful parallel in there somewhere...
 
Originally Posted By: punisher
Pretty much what KGMtech posted. Avoid the "high vac" revs like downshifting from 5th to 2nd and dropping the clutch at 50mph. Lots of difference in rod loading from WOT RPM to the same RPM with no load.


Not really. The most common rod failure is because of stretched bolts as the piston reached TDC at high RPM. Yes, the compression load helps on the intake and power strokes, but does nothing for the exhaust stroke and that;s when all hades breaks loose...

It just that redline in neutral at high vacuum does not offer any compression cushion on any stroke. But, if the bolts are going to fail, they will do so at redline no matter how your look at it.

Redline is an engineering load. It is not best performance line. Best performance is often obtained by going just far enough past the TQ peak to land squarely on the TQ peak when you hit the next gear. That is usually shifting slightly short of redline
smile.gif
 
Originally Posted By: BrocLuno
punisher said:
....Redline is an engineering load. It is not best performance line. Best performance is often obtained by going just far enough past the TQ peak to land squarely on the TQ peak when you hit the next gear. That is usually shifting slightly short of redline
smile.gif



This. On my stock LS1, "spirited driving" means from 3000-4500 rpm, despite a red line of 5500-6200 rpm. For street driving who needs more than that? I spend most of the time at 1500-2800 rpm. I rarely go over 4500 rpm where torque peaks out....and I like my bottom end staying intact. Not to red line.
 
Originally Posted By: BrocLuno


Redline is an engineering load. It is not best performance line. Best performance is often obtained by going just far enough past the TQ peak to land squarely on the TQ peak when you hit the next gear. That is usually shifting slightly short of redline
smile.gif



I've had an egine where I chose to increase the rev limiter from 6500 to 6900 rpm to get closer ot the peak rpm in the next gear. Especially at lower gears the rpm fall is big and this engine officially had it's torque peak at 5000 RPM, though on the dyno it made 99% of that at 4500 rpm, and that's where I wanted to be in the next gear.

Even at 8000 rpm the negine didn't explode though, so besides from dwindling power there was no issue with extending the rev limiter, and it did help me to get my highest top speed ever: 153 mph @ 6800 rpm in 5th gear, from an NA 2.0 8v engine.
 
All my cars see redline on every trip I take. If they don't it's usually because of a passenger, bad weather, or it's an ultra short trip.
 
There's no reason to redline an engine. It also is hard on the transmission.
 
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Originally Posted By: fdcg27
I suspect that this is nonsense.
While almost any engine seems to run better after the occasional hard run through a few gears, constant operation at high revs will cause higher wear and it matters not whether the engine was made by BMW or Chevrolet.
Driving gently except for those times where it's necessary or desirable to run the engine hard will prolong its life.
Running hard for grins now and then is fun and perfectly fine, but I wouldn't consider it either necessary or desirable to keep the revs up at all times in typical driving.
More BMW engines are probably ruined by owners using the wrong oil on long drain intervals than by being babied.


I agree 100%.
 
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