I scanned for over-revs... here are results, what u guys think?
#31
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Maybe it's not the correct word to use - momentum - but I don't see how the rev limiter can stop the engine at exactly the defined rpm limit when you are moving through the gears in a spirited manner. Not that I would try this, but if you reved the engine by blipping the throttle while stationary, would the rev limiter stop the engine at exactly 7,200 (if that were the limit)? I think not so if it goes to 7,205 you would record a range 1 over-rev. Sorry i didn't pay attention in physics class and even if i did it was so long ago that i don't remember anything anyway.
#32
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What if the dealer CPO'd the car with range 4 and 5 readings and disclosed the readings prior to sale?
#33
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Not so sure how an engine can speed up by "momentum". Momentum is the description of an object in motion to stay in motion unless acted on by an outside source. It takes power to make the engine rotate and more power is required to make it rotate faster. If the rev limiter cuts the power at X RPMs than the "momentum" RPMs would remain at X until friction slows it down. If you throw a ball straight up in the air its V max will be the instant it leaves your hand. Ball will accelerate only from the start of the throw until you release it. How far it travels up will be a function of its final V, but it will not go any faster than the release point.
#34
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Bad example. the clutch disconnects the gearbox from the engine so all of a sudden the engine has nothing to work against and therefore speeds up for a very short time. If you watch an off shore boat race, every time the propellers get out of the water (nothing fighting vs the engine) the throttle man has to cut the throttles off or else the engine would increase revs and break. Same concept here except it's not water
It takes power to accelerate to a given speed/rpm. Acceleration, weather radial as in RPMs increase or linear as in a launch, requires power. Remove power and acceleration stops. Load on the engine has nothing to do with it. Settings of the rev limiter have EVERYTHING to do with it.
#35
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I asked your very question to the local service manager of the car I noted in my earlier post. His response was that even though the car was CPOd by another dealership, he was confident the Porsche rep would refuse a major warranty claim (engine) as he had seen this happen before. I pressed him on that point - citing that the DME indicated abouse prior to the CPO date, and that the car should not have been CPOd. His response - "these things happen, this is not an exact science"...
Caveat emptor....
-B
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#37
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#38
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Brilliant point... The problem is the subjectivity of this issue. I would imagine that the selling dealership would be more inclined to honor the CPO that they "certified" than a dealer out of geography who has a different Porsche zone rep approving warranty work.
I asked your very question to the local service manager of the car I noted in my earlier post. His response was that even though the car was CPOd by another dealership, he was confident the Porsche rep would refuse a major warranty claim (engine) as he had seen this happen before. I pressed him on that point - citing that the DME indicated abouse prior to the CPO date, and that the car should not have been CPOd. His response - "these things happen, this is not an exact science"...
Caveat emptor....
-B![Wink](https://rennlist.com/forums/images/smilies/wink.gif)
I asked your very question to the local service manager of the car I noted in my earlier post. His response was that even though the car was CPOd by another dealership, he was confident the Porsche rep would refuse a major warranty claim (engine) as he had seen this happen before. I pressed him on that point - citing that the DME indicated abouse prior to the CPO date, and that the car should not have been CPOd. His response - "these things happen, this is not an exact science"...
Caveat emptor....
-B
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#39
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Range 1: 7300-7500 RPM
Range 2: 7500-7700 RPM
Range 3: 7700-7900 RPM
Range 4: 7900-8400 RPM
Range 5: 8400-9500 RPM
Range 6: 9500-11000 RPM
At 7200 RPM you have 120 revs per second X 3 ignitions per revolution or 360 ignitions per second.
Let's assume a car has the following time in each rev range, assuming the midpoint of each range as the actual RPM.
Range 1 - 3,603 ignitions / 370 per second = 9.74 seconds
Range 2 - 407 ignitions / 380 per second = 1.07 seconds
Range 3 - 36 ignitions / 390 per second = 0.09 seconds
As has been stated earlier, ranges 1 - 3 should not cause you any problems with engine damage or with the warranty. Range 4 gets into the gray area, but revs in Ranges 5 and 6 are red flags for the potential to have the engine warranty voided by Porsche.
Hope this helps.
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When I last spoke with someone at PCNA I was told that it was not possible to damage the engine with the throttle. Cannot prevent a blown shift though.
I think it may be possible to make some sort of robo gate thingy that would prevent a downshift if revs are wrong. Prob open a can of worms that would lead to all sorts of bad things.
I think it may be possible to make some sort of robo gate thingy that would prevent a downshift if revs are wrong. Prob open a can of worms that would lead to all sorts of bad things.
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If you miss a shift (going from 5 to 2 instead of 4) the transmission will cause the revs to go beyond red line. That is called a "money shift" because if the engine revs high enough, it could cause severe damage the the valves, pistons and valve shafts, resulting in a lot of $$$$ to repair.
#45
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Hi Tim
I do believe your analogy is flawed.
When you brake at no time does your speed INCREASE. You could correctly say that your engine would not STOP immediately when fuel is cut, but increase in RPM??
Can you point me in the direction of the physics behind an engine continuing to increase in RPM after fuel has been cut?
Thanks
I do believe your analogy is flawed.
When you brake at no time does your speed INCREASE. You could correctly say that your engine would not STOP immediately when fuel is cut, but increase in RPM??
Can you point me in the direction of the physics behind an engine continuing to increase in RPM after fuel has been cut?
Thanks