997 GT2 slight stumble under boost
#1
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I've put 35,000 very enjoyable miles on my '07 997 GT2. Made a few minor upgrades along the way. EVOMS tune, which immediately made the clutch slip. Then GT2RS single mass clutch and lightweight flywheel(cured the slip). Guard diff, GT2RS Intercoolers, That's about it. I drive it pretty hard occasionally and it had been running flawlessly for years. Just recently I started feeling a brief hesitation for about a half second after going to full throttle / full boost in say 3rd or 4th gear. The car would just slightly hesitate then get right back to business. At first I thought nothing of it, maybe bad gas or something, but it continues to happen after a couple fresh tanks from different sources. Last weekend I set the dash display on digital boost to have a look at what was going on (which can be tricky taking your eyes off the road at full boost in 4th). I saw 20psi initially, then the stumble hit and boost went to 19, then right back to 20 and business as usual. Has anyone here experienced this before and found the problem? It could be a VTG problem, waste gate, boost leak, even coils?
Last edited by Johnb55; 09-14-2017 at 12:56 PM.
#2
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Have you checked codes?
Not a Porsche, but my last turbo engined car had a stumble on full boost just like you describe. Turned out to be bad bearings on the turbo impeller so the turbo needed a rebuild.
Not a Porsche, but my last turbo engined car had a stumble on full boost just like you describe. Turned out to be bad bearings on the turbo impeller so the turbo needed a rebuild.
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OP, nice description! Can very much visualize the issue with your description.
#4
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Spark plugs & ignition coils is good place to start. Pretty common thing with tune; more power = higher cylinder pressure = drawing more current from spark plugs & ignition coils.
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TPC Racing stats:
2023 Porsche Sprint Challenge 992 Cup Am Champion
2023 Porsche Sprint Challenge GT4 Pro-Am Team Champion
2022 Porsche Sprint Challenge 992 Cup & 991 Cup Champion
2020 IMSA GT3 Cup Challenge 2nd Championship
2018 IMSA GT3 Cup Challenge 2nd Championship
2016 IMSA GT3 Cup Challenge Champion
2013 IMSA GT3 Cup Challenge Champion
2006 Rolex-24 @ Daytona GT Champion
2004 Grand-Am SGS Class Champion
#7
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Could you report back what if any codes you have ?
My first thought was spark plugs also, they tend to wear out quite quickly on stage 1 (style) tuned 7GT2s, lots of timing and quite lean produces the extra hp IIRC.
My first thought was spark plugs also, they tend to wear out quite quickly on stage 1 (style) tuned 7GT2s, lots of timing and quite lean produces the extra hp IIRC.
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#8
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OP,
Out of curiosity, with that kind of tune what kind of peak boost do you see on the digital read out?
(I think that my stock 7GT2 I've seen 21psi or maybe 20 psi? It has been a while. I think that i get the same on my GT2RS, I was told due to large IC. And on my 997TT it was 17 psi on over-boost, this car is now sold).
Out of curiosity, with that kind of tune what kind of peak boost do you see on the digital read out?
(I think that my stock 7GT2 I've seen 21psi or maybe 20 psi? It has been a while. I think that i get the same on my GT2RS, I was told due to large IC. And on my 997TT it was 17 psi on over-boost, this car is now sold).
#9
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OP,
Out of curiosity, with that kind of tune what kind of peak boost do you see on the digital read out?
(I think that my stock 7GT2 I've seen 21psi or maybe 20 psi? It has been a while. I think that i get the same on my GT2RS, I was told due to large IC. And on my 997TT it was 17 psi on over-boost, this car is now sold).
Out of curiosity, with that kind of tune what kind of peak boost do you see on the digital read out?
(I think that my stock 7GT2 I've seen 21psi or maybe 20 psi? It has been a while. I think that i get the same on my GT2RS, I was told due to large IC. And on my 997TT it was 17 psi on over-boost, this car is now sold).
The RS runs at 1.6 bar max (23/24PSI) from factory so presumably its dash readout can read higher although I have no idea if it does ? the increase to 1.6 bar has nothing to do with the fact the intercooler may be physically larger but that larger intercooler (because of its efficiency) does allow it to operate at higher boost pressure and produce power (I think you probably know/meant that
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#11
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I've put 35,000 very enjoyable miles on my '07 997 GT2. Made a few minor upgrades along the way. EVOMS tune, which immediately made the clutch slip. Then GT2RS single mass clutch and lightweight flywheel(cured the slip). Guard diff, GT2RS Intercoolers, That's about it. I drive it pretty hard occasionally and it had been running flawlessly for years. Just recently I started feeling a brief hesitation for about a half second after going to full throttle / full boost in say 3rd or 4th gear. The car would just slightly hesitate then get right back to business. At first I thought nothing of it, maybe bad gas or something, but it continues to happen after a couple fresh tanks from different sources. Last weekend I set the dash display on digital boost to have a look at what was going on (which can be tricky taking your eyes off the road at full boost in 4th). I saw 20psi initially, then the stumble hit and boost went to 19, then right back to 20 and business as usual. Has anyone here experienced this before and found the problem? It could be a VTG problem, waste gate, boost leak, even coils?
#12
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OP,
Out of curiosity, with that kind of tune what kind of peak boost do you see on the digital read out?
(I think that my stock 7GT2 I've seen 21psi or maybe 20 psi? It has been a while. I think that i get the same on my GT2RS, I was told due to large IC. And on my 997TT it was 17 psi on over-boost, this car is now sold).
Out of curiosity, with that kind of tune what kind of peak boost do you see on the digital read out?
(I think that my stock 7GT2 I've seen 21psi or maybe 20 psi? It has been a while. I think that i get the same on my GT2RS, I was told due to large IC. And on my 997TT it was 17 psi on over-boost, this car is now sold).
997 GT2's have two different boost readouts to select from on the dash. A bar graph that goes from 0 to 20 psi, and a digital readout that just displays the number which is probably not limited. The highest I've seen on the digital display is 21 psi. I don't recall what it was stock, maybe 19?
#14
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I have the basic EVOMS EVT 600 tune, software only. I think it changes the timing and fuel maps, adds a couple hundred rpm to the rev limit and increases boost a little. They claim +62 hp which I took with a grain of salt. They told me I would need to upgrade the clutch as the added power would make it slip. I replied, "yeah, we'll see..." Well it did immediately start slipping under full throttle in 4th and 5th so I upgraded to a single mass clutch and lightweight flywheel. I now take their claims a little more seriously. They have other tunes paired with headers, high flow cats, intercoolers, and even different turbos that go up to 754 claimed hp.
997 GT2's have two different boost readouts to select from on the dash. A bar graph that goes from 0 to 20 psi, and a digital readout that just displays the number which is probably not limited. The highest I've seen on the digital display is 21 psi. I don't recall what it was stock, maybe 19?
997 GT2's have two different boost readouts to select from on the dash. A bar graph that goes from 0 to 20 psi, and a digital readout that just displays the number which is probably not limited. The highest I've seen on the digital display is 21 psi. I don't recall what it was stock, maybe 19?
Tuning the stock GT2 is about temperature control with those pesky VTGs creating lots (of heat) A GT2 will run the 620PS of the GT2RS with just the addition of RS/997.2 intercoolers and appropriate mapping but even the RS will lose its 620PS rating if used aggressively in higher ambient temps, the ECU is highly efficient at stealing your hp oce the IATs head over 40C.
The dash numbered boost gauge is also limited to 1.4bar, won't read any higher.
#15
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Update:
I picked my GT2 up from service today. New plugs and coils, plus oil change and cabin filters.
The tech said most of the coils were cracked and there was evidence of some arcing. The car has just under 36,000 miles and the coils had never been replaced previously.
I gave it the old boost test and it ran stumble free showing 21 psi of boost the whole way. Here's what I saw in the mirror![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
Good call on coils and plugs you guys, I hope this thread is helpful to someone in the future.
I picked my GT2 up from service today. New plugs and coils, plus oil change and cabin filters.
The tech said most of the coils were cracked and there was evidence of some arcing. The car has just under 36,000 miles and the coils had never been replaced previously.
I gave it the old boost test and it ran stumble free showing 21 psi of boost the whole way. Here's what I saw in the mirror
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
Good call on coils and plugs you guys, I hope this thread is helpful to someone in the future.