Lightweight flywheel casing overrevs?
#1
Lightweight flywheel casing overrevs?
Hi all,
I'm looking at a 997.1 turbo with a pretty reasonable pricetag, but the owner says the lightweight flywheel has caused false readings of level 5 and 6 overrevs. I know he tracked the car, which he is stating up front, and thus the price. Has anyone else heard of a lightweight flywheel causing false DME readings???
I'm looking at a 997.1 turbo with a pretty reasonable pricetag, but the owner says the lightweight flywheel has caused false readings of level 5 and 6 overrevs. I know he tracked the car, which he is stating up front, and thus the price. Has anyone else heard of a lightweight flywheel causing false DME readings???
#2
Rennlist Member
Hi all,
I'm looking at a 997.1 turbo with a pretty reasonable pricetag, but the owner says the lightweight flywheel has caused false readings of level 5 and 6 overrevs. I know he tracked the car, which he is stating up front, and thus the price. Has anyone else heard of a lightweight flywheel causing false DME readings???
I'm looking at a 997.1 turbo with a pretty reasonable pricetag, but the owner says the lightweight flywheel has caused false readings of level 5 and 6 overrevs. I know he tracked the car, which he is stating up front, and thus the price. Has anyone else heard of a lightweight flywheel causing false DME readings???
Peter
#3
Sounds like BS to me - however I'm not really familiar with the 997 or Porsches in general. That said, assuming a manual transmission, there is no way with proper driving for a lightweight flywheel to cause an over-rev. It certainly could be more likely to do this doing some boy-racer ****, i.e. revving the motor in neutral. If motor RPM is not sensed at the flywheel, I have a hard time believing "false DME" RPM readings - RPM is RPM.
How big is a "level 5 and 6 overrev"? I'd be very wary.
-Mike
How big is a "level 5 and 6 overrev"? I'd be very wary.
-Mike
#4
Addict
Rennlist Member
Rennlist Member
It is possible to over rev a motor through the rev limiter by 300-400 RPMs in an upshift if you are clutching in before you are off the throttle. I see that in PCA Club Racing Data all the time and we tend to ignore it for compliance checking. HOWEVER, this would not produce Level 5 or 6 over-revs which in your case would be 8000+ RPMs - there is only one way to get there. . There are 997 turbo over-rev charts all over the internet. Not sure how legit they are.
#5
Rennlist Member
Sounds fishy. Are we talking about 1 or 2 level 5 and 6 or a whole bunch?
Even throttle blips on a downshift shouldn't be getting that high!
I'm guessing a money shift but I'm not an expert.
Even throttle blips on a downshift shouldn't be getting that high!
I'm guessing a money shift but I'm not an expert.
#6
Rennlist Member
It is possible to over rev a motor through the rev limiter by 300-400 RPMs in an upshift if you are clutching in before you are off the throttle. I see that in PCA Club Racing Data all the time and we tend to ignore it for compliance checking. HOWEVER, this would not produce Level 5 or 6 over-revs which in your case would be 8000+ RPMs - there is only one way to get there. . There are 997 turbo over-rev charts all over the internet. Not sure how legit they are.
#7
Thanks, everyone, for all of your replies. The seller has not yet provided me with the actual data, other than saying it looks "like a mess" with several level 5 and 6 overrevs, and that his mechanic says that's normal with a LW flywheel. I figured that was BS as well. My guess is it was downshifted into the wrong gear multiple times. I'm curious about what would happen first, valve float or a damaged crank/rod bearing.
Assuming no cylinder damage, how much would it cost to have the engine rebuilt?
I guess I don't feel like my pockets are deep enough to replace an entire engine. From a resale value, I also guess I don't want to try making up some BS story about a LW flywheel for the next guy to ponder.
I'll keep looking. I'm sure I'll have more questions for you guys soon.
Thanks,
-Tom
Assuming no cylinder damage, how much would it cost to have the engine rebuilt?
I guess I don't feel like my pockets are deep enough to replace an entire engine. From a resale value, I also guess I don't want to try making up some BS story about a LW flywheel for the next guy to ponder.
I'll keep looking. I'm sure I'll have more questions for you guys soon.
Thanks,
-Tom
Trending Topics
#8
Rev limiters are not a catch all. In my E36 race car, it's valves were damaged when the shift mechanism failed and it was over-reved because the driver planted the throttle on the floor in neutral. Minor damage that was repaired before I got the car. Bottom line is that it is quite possible to over-rev a "rev limited" motor with the right circumstances.
-Mike
#9
Rennlist Member
Keep in mind a level 6 over rev in a 997 turbo is >9000 rpm. That seems way past redline for simple momentum in a non-lift shift.
Range 1">Range 2Range 3Range 4Range 5Range 6
> 6800 and < 7000> 7000 and < 7200 > 7200 and < 7400 > 7400 and < 7900 > 7900 and < 9000 > 9000
Range 1">Range 2Range 3Range 4Range 5Range 6
> 6800 and < 7000> 7000 and < 7200 > 7200 and < 7400 > 7400 and < 7900 > 7900 and < 9000 > 9000
#10
Addict
Rennlist Member
Rennlist Member
.
#12
Race Director
what you are being told is bs. That said, there is some glitch on the 997 computer that will show a handful of overrevs in certain categories. The trick here is that they will be single digits and similar in number or the higher category being higher than the lower (physically impossible). For instance, my 7tt has 3 overrev ignitions in both ranges 4 and 5, which is impossible. Post the info once you get it and we'll see.
#14
Rennlist Member
Frank, i see the graph, but how is this even remotely possible? if the throttle closes, there is no more increase in power, how does the engine increase rpm with no added energy? It reminds me of the graphs of dyno runs. the graph shows jumps in RPM at the end of a high power pull, but it is just electrical noise.
what you are being told is bs. That said, there is some glitch on the 997 computer that will show a handful of overrevs in certain categories. The trick here is that they will be single digits and similar in number or the higher category being higher than the lower (physically impossible). For instance, my 7tt has 3 overrev ignitions in both ranges 4 and 5, which is impossible. Post the info once you get it and we'll see.
#15
Rennlist Member
In the situation you were responding to a shift is made at redline where the driver does not completely get off the throttle before pushing in the clutch. At the point where the engine unloads, it's RPM will go past redline before the DME can cut the fuel off - think of it as a mini moneyshift in that the engine is setup to overrev and there is nothing the DME can do about it. A lighter flywheel will make this case worse and I would also classify this case as "improper driving".
Rev limiters are not a catch all. In my E36 race car, it's valves were damaged when the shift mechanism failed and it was over-reved because the driver planted the throttle on the floor in neutral. Minor damage that was repaired before I got the car. Bottom line is that it is quite possible to over-rev a "rev limited" motor with the right circumstances.
-Mike
Rev limiters are not a catch all. In my E36 race car, it's valves were damaged when the shift mechanism failed and it was over-reved because the driver planted the throttle on the floor in neutral. Minor damage that was repaired before I got the car. Bottom line is that it is quite possible to over-rev a "rev limited" motor with the right circumstances.
-Mike
to your second point. no, sorry, you cant over rev your car in neutral. the rev limiter cuts out at exactly its set point. it doesnt matter how fast it revs to the that set point, the DME can easily cut fuel when it hits it and there is no "momentum" force that supersedes the physics. you need F, to make m , a. (a=F/m)