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Old 09-18-2005, 07:55 PM   #1
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Hit the Rev Limiter

I hit the Rev Limiter on accident today. Any damage that I might need to be aware of? She seems to be driving fine and I didn't notice any changes.

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Old 09-18-2005, 08:30 PM   #2
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Hi,

Nope, that's what the Rev Limiter is for - to pull the plug before you blow-up the motor.

So long as the engine is in good tune and overall good shape, and your oil & coolant levels are good, you can bounce off the Rev Limiter all day.

Happy Motoring!...Jim'99

PS BTW, Helicopters don't Fly, they beat the air into submission!

Last edited by MNBoxster; 09-18-2005 at 08:33 PM.
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Old 09-18-2005, 09:36 PM   #3
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As long as it was on the upshift and not the downshift you are okay. Which, I guess it was since you said it bounced off redline.
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Old 09-19-2005, 03:57 AM   #4
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"So long as the engine is in good tune and overall good shape, and your oil & coolant levels are good, you can bounce off the Rev Limiter all day":

Well, not really. I can think of several negatives here:

1-Even if you engine doesn't blow at that time, you are shortening your overall engine life. Wasting tons of gas too!

2-Each trip to the rev limiter is recorded by the ECU. This is read when you get your car serviced at Porsche and if you are under warranty, can SOMETIMES be used to deny an engine warranty claim. The data becomes part of your PERMANENT RECORD!

3-If you are going this fast all the time, the Police and the local tire dealer will be your best friends!

Happy motoring!

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Old 09-19-2005, 05:15 AM   #5
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I rarely engage in that type of driving, in fact, I was trying to merge on the highway and wasn't paying attention to what gear I was in because an 18 wheeler was trying to be a funny guy and not let me on. Anyway, I hit the gas not realizing what gear I was in and hit the limiter.

I am very conscious about my driving style because I DO NOT want to be one of those horror stories where Porsche decides not to honor its warranty.
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Old 09-19-2005, 05:38 AM   #6
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Sounds very sensible to me!

Good driving!





Quote:
Originally Posted by Rail26
I rarely engage in that type of driving, in fact, I was trying to merge on the highway and wasn't paying attention to what gear I was in because an 18 wheeler was trying to be a funny guy and not let me on. Anyway, I hit the gas not realizing what gear I was in and hit the limiter.

I am very conscious about my driving style because I DO NOT want to be one of those horror stories where Porsche decides not to honor its warranty.
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Old 09-19-2005, 09:18 AM   #7
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@BruceLee,

I agree with you on points 2 & 3, but these are consequential, not Mechanical, issues to hitting the Rev Limiter, and I took the lister's queery to mean the Mechanical issues.

I disagree with you on item 1. There is no problem running the Engine at these speeds. The engine was designed to operate at this speed. The Performance numbers are derived from this. Peak HP is usually at or near Red Line. It does not increase the wear on the Engine, assuming, as I previously stated, that the overall condition of the Engine is good and that the fluid levels are proper. According to your reasoning, it would be better to operate the car at idle than any other RPM and we know this isn't the case. Engine Cooling and Lubrication are Crank Speed dependent (the Waterpump and Oil Pump are powered off the Crankshaft), so running at higher RPMs insures that these systems are operating at 100%. This is the primary reason why idling your car excessively will induce greater wear.

Plus, the manufacturer most always adds a Fudge Factor when determining a Rev Limit to minimize warranty claims and the like. I once spoke with a Lotus Engineer about my Esprit which hits the limiter at 7,200RPM. He stated that the engine was good for about 9,000RPM before there were any problems. And, that at 9,000 RPM, it was the Ancillaries (Alternator, Waterpump, AC Compressor), not the Engine, which were the limiting factor. He further said that only at about 11,000RPM were there any Engine problems, and this from the valvetrain, not the Reciprocating gear.

@LexusPilot,

I agree with you re. Upshift vs. Downshift. But want to point out that upon downshifting improperly, it is possible to exceed Red Line RPMs, there is no Mechanical safeguard in place to prevent this from happening.

Happy Motoring!...Jim'99
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Old 09-19-2005, 09:22 AM   #8
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Quote:
Originally Posted by MNBoxster
I agree with you re. Upshift vs. Downshift. But want to point out that upon downshifting improperly, it is possible to exceed Red Line RPMs, there is no Mechanical safeguard in place to prevent this from happening.
Please help uneducated here. I don't understand why downshifting allows you to over rev? I thought the limiter was rpm dependent.
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Old 09-19-2005, 09:39 AM   #9
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Originally Posted by gRed04
Please help uneducated here. I don't understand why downshifting allows you to over rev? I thought the limiter was rpm dependent.

Hi,

A Rev Limiter prevents the Engine from making too high revs, but it doesn't prevent it from actually spinning that high.

A Rev Limiter usually works in one of two ways. It can completely cut out the Ignition Spark and/or Fuel Pump (this is referred to as a Hard Limiter) and the engine suddenly stops making power and subsequently very quickly drops below Max RPM). Or, the ECU (DME in Porsche Parlence) will selectively cutout every other cylinder (referred to as a Soft Limiter) which again, drops the RPMs back into the safe range.

But, if you are downshifting, the speed of the Rear Wheels can be exceeding the RPM range for the Engine. When you let out the clutch, you can cause the Crankshaft to turn at the same speed as the Transmission's Primary Shaft. Since the Engine itself isn't doing this, cutting the Spark and Fuel will have no effect, and the Engine can spin higher than Max allowable RPMs. But, you'll probably tear up the Clutch, Throwout Bearing and such, so you'll have a plateful of issues to deal with. Hope this helps...

Happy Motoring!...Jim'99

Last edited by MNBoxster; 09-19-2005 at 09:46 AM.
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Old 09-19-2005, 11:13 AM   #10
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Based on several studies conducted, overall engine life is correlated inversely with average RPM and % of throttle utilized, ie acceleration rates.

Simply put, reving the engine like a mad man and hammering the throttle shortens engine life.

The last study on this subject was in Panorama magazine some months back and the source was ........Porsche.




Quote:
Originally Posted by NBoxster
@BruceLee,

I agree with you on points 2 & 3, but these are consequential, not Mechanical, issues to hitting the Rev Limiter, and I took the lister's queery to mean the Mechanical issues.

I disagree with you on item 1. There is no problem running the Engine at these speeds. The engine was designed to operate at this speed. The Performance numbers are derived from this. Peak HP is usually at or near Red Line. It does not increase the wear on the Engine, assuming, as I previously stated, that the overall condition of the Engine is good and that the fluid levels are proper. According to your reasoning, it would be better to operate the car at idle than any other RPM and we know this isn't the case. Engine Cooling and Lubrication are Crank Speed dependent (the Waterpump and Oil Pump are powered off the Crankshaft), so running at higher RPMs insures that these systems are operating at 100%. This is the primary reason why idling your car excessively will induce greater wear.

Plus, the manufacturer most always adds a Fudge Factor when determining a Rev Limit to minimize warranty claims and the like. I once spoke with a Lotus Engineer about my Esprit which hits the limiter at 7,200RPM. He stated that the engine was good for about 9,000RPM before there were any problems. And, that at 9,000 RPM, it was the Ancillaries (Alternator, Waterpump, AC Compressor), not the Engine, which were the limiting factor. He further said that only at about 11,000RPM were there any Engine problems, and this from the valvetrain, not the Reciprocating gear.

@LexusPilot,

I agree with you re. Upshift vs. Downshift. But want to point out that upon downshifting improperly, it is possible to exceed Red Line RPMs, there is no Mechanical safeguard in place to prevent this from happening.

Happy Motoring!...Jim'99
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Old 09-19-2005, 12:10 PM   #11
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The engine should be able to take frequent revs. It's a Porsche and part of the driving experience is "spirited" driving.
Having said that, the history books are filled with cars that did, and did not, meet the standard. Triumph TR4 and TR6 engines were noteworthy for their reliability (yep, much of the rest of the cars were junk). The GT6 was known as frail - the transmissions and gearboxes couldn't take the load of the 6 cylinder engines. History will judge the Boxsters honestly and openly (this differs from a marketer's hype or the lawyer's esculpatory warnings).
Second thought: there was much concern in a recent thread on rev-matching so as not to load the drive train. Frequent accelerations also load the drivetrain. Still, a Boxster should be able to take repeated accelerations, braking, and even downshifting - all normal attributes of spirited driving. Equally true though, if you can drive "smoothly", it will last even longer. On the road or on the track, smoothness counts.
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Old 09-19-2005, 06:53 PM   #12
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So then what would be better:

The lack of revs(storing a car long enough for moisture to work it's magic)

or

Hitting the rev limiter.

The $65,000 question.

Actually Rail, this rev limit bounce is only a problem for the person who buys your car
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Old 09-20-2005, 06:42 AM   #13
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"The lack of revs(storing a car long enough for moisture to work it's magic)"

From the standpoint of engine longevity, this is probably not the correct way to frame it. I am certainly not suggesting you park your Porsche to preserve it.

I think the data shows that driving your Porsche to the red line on a daily basis will certainly shorten the drive train's life vs. a more prudent way of driving.

This is supported both in theory and in practice.

To wit, the useful life of just about any race car is very very short, even though these cars are built to specifically run at top RPMS (blue printed engines, forged metals, oil changes at every race etc.).

If running these cars at top RPM was "good for them" they would have a nice long lifespan.

They do not.

Nor will your Porsche if you hammer it day in and day out.

I am not suggesting that you leave it in the garage or not engage in spirited driving. Simply understand that trips to the rev limiter create a cost.

If this were NOT true, why would Porsche keep track of these trips for warranty purposes?

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Old 09-20-2005, 07:03 AM   #14
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Quote:
Originally Posted by Brucelee
"The lack of revs(storing a car long enough for moisture to work it's magic)"

From the standpoint of engine longevity, this is probably not the correct way to frame it. I am certainly not suggesting you park your Porsche to preserve it.

I think the data shows that driving your Porsche to the red line on a daily basis will certainly shorten the drive train's life vs. a more prudent way of driving.

This is supported both in theory and in practice.

To wit, the useful life of just about any race car is very very short, even though these cars are built to specifically run at top RPMS (blue printed engines, forged metals, oil changes at every race etc.).

If running these cars at top RPM was "good for them" they would have a nice long lifespan.

They do not.

Nor will your Porsche if you hammer it day in and day out.

I am not suggesting that you leave it in the garage or not engage in spirited driving. Simply understand that trips to the rev limiter create a cost.

If this were NOT true, why would Porsche keep track of these trips for warranty purposes?

Hi,

I think your argument is somewhat superfluous. Your Race car analogy is somewhat off base as this is a car who's Engine differs in many ways to a Street Car Engine, such as in Compression, Timing, A/F mix, etc. Apples to Oranges. Besides that, a Race Car Engine is run about 75%-80% of the time at Red Line (if you plan on being Competitive), whereas we're only discussing occaisionally, or accidentally, bouncing off the Rev Limiter.

Lexuspilot has taken your logic to extreme, but he's not all wrong. Simply turning the key will eventually wear out the Engine. That's what Engine's do, they wear out, no matter how well you care for them, eventually all the heat and friction takes their toll.

I don't dispute that empirically you increase wear and/or shorten the Life of the Engine. But, you need to put some perspective to this. You may have a rebuild due at 100K rather than at 120k. That doesn't mean it's gonna Blow-up tomorrow.

Plus, there are many other ways of ignoring or abusing your Engine which will shorten it's life much sooner such as running low on fluids, buying Bad Gas, not allowing it to warmup sufficiently when it's cold, (which is probably the greatest sin committed - You know that little Blue mark on your temp gauge? You're supposed to allow the Temp Needle to travel North of it before driving, how many people do this consistently?).

No, I am not convinced that hitting the Rev Limiter, even on a consistent basis is much to worry about so long as you look after the car's Tune and Fluids. Every Engine I've ver seen Blow-up was from some other type of abuse, usually neglect.

Happy Motoring!...Jim'99
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Old 09-20-2005, 07:43 AM   #15
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"No, I am not convinced that hitting the Rev Limiter, even on a consistent basis is much to worry about so long as you look after the car's Tune and Fluids. Every Engine I've ver seen Blow-up was from some other type of abuse, usually neglect."

I understand that you are not convinced and that is not my intention. You can drive your car off the rev limiter everyday and that is fine with me. However, it is factual that heat, friction and mechanical stress all act to increase wear in ANY engine, not matter how well maintained. Same applies to the drivetrain. So, all of these increase greatly as revs climb and the gas pedal goes rapidly to the floor.

As long as you understand that you are shortening your engine life, that is fine as it is your car.

Don't delude yourself into thinking that keeping your oil clean and plugs new is going to eliminate this "cost" as it will not. It will help but there is not cheating the man!

Also keep in mind that blowing up an engine and decreasing useful life are not necessarily the same thing. However, I would bet more engines "blow up" at red line than at 2500 rpms.

Lastly, if I understand your point about engine warm up correctly, it conflicts with every professional's advice that I have seen, which is to allow your cold engine to run about 10 seconds, drive off slowly and allow the engine to warm up quickly under light load.

AFTER the engine is fully warm, one can get more aggressive with driving.

If I understand what you are advocating, you would sit in the driveway until the temp gauges moves. Did I get that right?

If so, this theory went out with the 60s I believe.
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Old 09-20-2005, 09:24 AM   #16
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Continuing the debate -
Rail, IMHO, bouncing the rev limiter did no damage to your car.
Warm-up: Not as critical as it used to be, for starting and driving normally. I think the manual even says you can turn the key and go. As an old-schooler, I still let my cars idle for 5-10 seconds before I pull away - it's just habit. Here's the distinction: I never drive hard (aggressive throttle, or above 3500 RPM) until the car is FULLY warmed. If the car has been sitting for 3 weeks, I warm it up carefully.
High RPMs: Yes, continuous high RPMs (the race car) will burn up a motor quicker than all gentle driving. But sports cars, like Porsches, should be able to take 100,000 miles of driving by Porsche owners. Running the revs up smoothly on a regular basis should not burn the car up prematurely.
Smooth is a key word. Slamming the drivetrain wears out parts. (Many an SUV'er does damage to the soccer van by rolling backwards and dropping the automatic into drive while still moving backwards. That's bad.)
Porsche and the Economics of Warranty Work: The rev limiter is an easy target because it's measurable. It's easy to say that high RPMs = abuse. Sometimes that's correct, and sometimes it's not. Running the revs up smoothly is a joy, and personally, I don't think that alone should blow my motor early. (Track time might, however, which I do. Explains why I have a car that's out of warranty - no one would touch it after repeated trips to the track. If it breaks I'll fix it.) But Porsche is erring on their safe side - not surprising, they are a business enterprise. It's probably true that some drivers lose some deserved warranty work solely because they rev'd out a few times, but equally true that other owners wring the crap out of the cars and then take it to the dealer to fix it under warranty. And the SUV owner that puts it in drive while rolling backward gets their car fixed under warranty, simply because there is no strain gage on the driveshaft. Yet.
Back to Rail: IMO, no mechanical damage done, but your dealer may try to convince you otherwise at some future moment.
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Old 09-20-2005, 09:46 AM   #17
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Lemon

As usual all good points.

According to my service shop, the computer tracks all overrevs.

This is not an automatic warranty no no.

However, if they see 50 or so of them,

Well........................

Good stuff.

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Old 09-20-2005, 02:35 PM   #18
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Correlation versus causation, the usual logical fallacy! High engine revs can't be shown to *cause* premature engine failure, but there are other htings to take into account. If you're the type of driver that likes to drive the car hard, there's a lot of other stress factors involved than just how many times you revved the engine.

But even if there is a correlation, that doesn't make me comfortable with Porsche using computer data that states how many times you've hit [whatever] RPM as a tool for denying warranty claims. It is not proof of any sort that you've mistreated the car... well, except for really obvious over-revving of course...
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Old 09-20-2005, 03:09 PM   #19
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Lets try this.

Does racing a car lengthen or shorten its useful life?

Do you want to buy a car that has been raced?

Does racing involve high revs and tremendous internal stresses?

Does daily trips to the redline lengthen or shorten an engines useful life?

Do manufacturer's in general have a qarranty disclaimer for racing or other forms of abuse?






Quote:
Originally Posted by eslai
Correlation versus causation, the usual logical fallacy! High engine revs can't be shown to *cause* premature engine failure, but there are other htings to take into account. If you're the type of driver that likes to drive the car hard, there's a lot of other stress factors involved than just how many times you revved the engine.

But even if there is a correlation, that doesn't make me comfortable with Porsche using computer data that states how many times you've hit [whatever] RPM as a tool for denying warranty claims. It is not proof of any sort that you've mistreated the car... well, except for really obvious over-revving of course...
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Old 09-20-2005, 05:34 PM   #20
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OK, let's say you were interested in buying a used Boxster from a Porsche dealer. And you wanted to see how many times, if any, the previous owner bounced off the Rev Limiter. If the dealer actually gave you the data (you could make the final sale conditional on this data) off the ECU (DME) how could you decifer the codes? Could you tell how many times they bounced off, if they gave you the data off the ECU??

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