Strange over rev report on GT4
12-21-2018, 11:35 AM
#31
Rennlist Member
This might be an interesting data point for reference even though there may be some differences in the ranges between GT4 and GTS. Do you have any estimation how you created so many Level 1's? Did you frequently rev to X,XXX RPM? Or did you frequently bang on the rev limiter which typically showed as X,XXX rpm?
Peter
12-21-2018, 06:43 PM
#32
Burning Brakes
this car has range 4 and 5 overrevs. this is a "don't buy".
unless there is documented bore scope and compression (and/or) leakdown testing within spec.
plenty of GT4s on this buyer's market. move along.
unless there is documented bore scope and compression (and/or) leakdown testing within spec.
plenty of GT4s on this buyer's market. move along.
12-21-2018, 07:02 PM
#33
Rennlist Member
Bingo, d00d hit it on the head!
To phrase d00d's astute statement - The only way you get an over rev above range 2 is if you miss-shift. e.g. somebody wanted 4th gear and got 2nd gear.
Although it is providing data about the engine, the DME read out is most valuable info about the transmission. Here somebody has thrust all that power through the transmission and it has only been 2 engine hours since. These are precision balanced parts and a transmission that has been buzzed could be an expensive repair. If you drive it and the transmission is tough or balky, anything but buttery smooth, then you know it has damage.
In addition, I believe this car cannot be CPO'ed because of the DME read out, is it possible this happened under the dealers watch?
To phrase d00d's astute statement - The only way you get an over rev above range 2 is if you miss-shift. e.g. somebody wanted 4th gear and got 2nd gear.
Although it is providing data about the engine, the DME read out is most valuable info about the transmission. Here somebody has thrust all that power through the transmission and it has only been 2 engine hours since. These are precision balanced parts and a transmission that has been buzzed could be an expensive repair. If you drive it and the transmission is tough or balky, anything but buttery smooth, then you know it has damage.
In addition, I believe this car cannot be CPO'ed because of the DME read out, is it possible this happened under the dealers watch?
As gregmorton notes, redline is 7800, so GT4 over rev ranges are the following;
1: 7800 - 8000
2: 8000 - 8200
3: 8200 - 8400
4: 8400 - 8600
5: 8600 - 8800
6: 8800 or more
The GT4's ECU doesn't add to the numbers when bouncing off the rev limiter, as in not shifting up soon enough, it only adds when an inappropriate downshift drags the revs up into the range.
1: 7800 - 8000
2: 8000 - 8200
3: 8200 - 8400
4: 8400 - 8600
5: 8600 - 8800
6: 8800 or more
The GT4's ECU doesn't add to the numbers when bouncing off the rev limiter, as in not shifting up soon enough, it only adds when an inappropriate downshift drags the revs up into the range.
12-21-2018, 10:17 PM
#34
Rennlist Member
12-27-2018, 01:45 PM
#35
I feel like a Flock of Seagulls wrote a song about this car...
12-28-2018, 03:06 AM
#36
Run away. So many other cars out there for sale.
12-28-2018, 12:57 PM
#37
Can someone explain to me how one could get an overrev past redline in a GT4 other than from a premature downshift. I assume that a rev limiter cuts in to prevent this. I'm new to the Porsche world, having owned my GT4 for less than a year. BMW, where I have spent all of my last 20 years, has a rev limiter that prevents overrev issues. Does my GT4 not have a rev limiter thereby allowing me to destroy the engine if I care to do so.
Along this line, how could anyone with a PDK say in a GT3 ever get any overrev. I presume with a PDK the rev limiter will prevent an overrev on throttle and the PDK won't allow a premature downshift into a lower gear. Wouldn't every GT3 PDK have a perfect DME report? If not, why not?
Along this line, how could anyone with a PDK say in a GT3 ever get any overrev. I presume with a PDK the rev limiter will prevent an overrev on throttle and the PDK won't allow a premature downshift into a lower gear. Wouldn't every GT3 PDK have a perfect DME report? If not, why not?
12-28-2018, 01:05 PM
#38
Rennlist Member
Can someone explain to me how one could get an overrev past redline in a GT4 other than from a premature downshift. I assume that a rev limiter cuts in to prevent this. I'm new to the Porsche world, having owned my GT4 for less than a year. BMW, where I have spent all of my last 20 years, has a rev limiter that prevents overrev issues. Does my GT4 not have a rev limiter thereby allowing me to destroy the engine if I care to do so.
However, 3 through 6 are from an inappropriate downshift.
12-28-2018, 01:24 PM
#39
Addict
Rennlist Member
Rennlist Member
12-28-2018, 03:34 PM
#40
Can someone explain to me how one could get an overrev past redline in a GT4 other than from a premature downshift. I assume that a rev limiter cuts in to prevent this. I'm new to the Porsche world, having owned my GT4 for less than a year. BMW, where I have spent all of my last 20 years, has a rev limiter that prevents overrev issues. Does my GT4 not have a rev limiter thereby allowing me to destroy the engine if I care to do so.
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SFZ GT3 (11-04-2022)
12-28-2018, 05:44 PM
#41
Rennlist Member
FWIW I would be fine with a car that has range 3 over revs (8200 - 8400). Range 4-5 I'd still consider but I'd want a compression test and some hours on the car since the last overrev. Low mile car with range 6 overrevs for sale at a discount is the perfect candidate for a 4.25l build 
12-28-2018, 07:25 PM
#42
Rennlist Member
FWIW I would be fine with a car that has range 3 over revs (8200 - 8400). Range 4-5 I'd still consider but I'd want a compression test and some hours on the car since the last overrev. Low mile car with range 6 overrevs for sale at a discount is the perfect candidate for a 4.25l build
12-28-2018, 10:44 PM
#43
Rennlist Member
It's because I get my car serviced there! Last time I went in for an oil change and came out with a 4L. This time I went in just to get my exhaust swapped and right there on the shop table was a new shiny set of 4.25L components and the 4.25L car on the dyno. I'm trying to resist but I'm a sucker for forged things. I could just get my car serviced at the stealer to avoid the temptation but then I'd probably end up in a new GT car every 9 months like everyone else on RL......
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SFZ GT3 (11-04-2022)
12-29-2018, 12:16 AM
#44
A rev limiter will cut fuel to keep you from revving too high via the throttle. Cutting the fuel means nothing if you are in 5th at 120mph and shift to 2nd. At that point you've made a mechanical connection and it's going to drive the engine to explode unless you get it back to neutral fast enough.
12-29-2018, 11:33 AM
#45
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What would happen if you planted your foot on the gas to the floor with the gearbox in neutral and starting with the engine at idle? If someone out there in internet land is curious enough to do that and risk their engine, please post video results here.
When I missed the 2-3 upshift as I described earlier, the RPM was already in the 6500+ range, and the rev limiter had no problem catching the engine RPM to prevent Range 3 ignitions. I think there were something like 14 ignitions in Range 2 and a couple hundred in Range 1 shown on the VAL report.