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Does anyone have some Sharktuner / SharkPlottler log data from a GTS they would like to share?
I have been learning to use the ST/SP tools on my GTS (X-pipe, 2.5" Exhaust, 30lb injectors) over the summer. It's been a good experience, and I've learned a lot about my specific car, and I have received excellent support from Jim Corenmam. However, I don't have any benchmark data to compare to. I am specifically interested in the presence of high-load knocks and what AFR / Ignition strategies people have taken to mitigate knock events under load. So if you have some log data, please share and provide some insights on your GTS mods as well as some commentary on what you did to address knock. I am particularly interested in GTS and similarly stroked engines to the GTS.
Also, I would appreciate any commentary can provide on GTS's and knock events. I have done some RL searches, and it would seem GTS engines are more prone to knock events than S3/S4/GT cars. Is this the case? Are GTS's motors more prone to knock events than S3/S4/GT engines? Are these knock events pre-detonations or some other acoustic event like pistons slapping on the cylinder walls?
These engines are like fingerprints. No two run exactly the same or have the same requirements.
What have you done to keep the majority of oil from reaching the intake system?
Did it work?
(This is job #1!)
Have you replaced the dampers and the regulators?
Which cylinders show knocks, in your data? (2,3,6,and 7 are the most common to see.)
These engines are like fingerprints. No two run exactly the same or have the same requirements.
What have you done to keep the majority of oil from reaching the intake system?
Did it work?
(This is job #1!)
Have you replaced the dampers and the regulators?
Which cylinders show knocks, in your data? (2,3,6,and 7 are the most common to see.)
RE: Oil Ingestion
Yes, very little oil is being consumed via the intake track now. I reinstalled the vacuum system and improved the oil separation steps before returning it to the intake. I added a series of 3 cyclonic separators before the provent. A paper towel test shows very little oil residue after several high-load runs and no visible oil under tame driving. Oil consumption is way down, and no more visible smoke out the tailpipe after hard runs. The piston heads are looking better than without the pump too. I know the pump is a little controversial and I'd like to get rid it as part of the engine rebuild.
The pistons were pretty heavily carbonized from removing the vacuum pump and restoring the stock breather. I ran some FI cleaner through the tank of case and that helped clean the pistons a little but nothing like prior to removing the pump. It might just take some time for the pistons to clean up. I can post some pics if needed.
RE: Fuel Pressure Regulators and Dampers
All three were replaced by the PO about 8,000 miles ago. They are OEM replacements, and the part numbers match the specifications. I vacuum-tested each during the intake refresh. They all held a vacuum. The fuel pressure and flow rate tests are also pasted with specifications. Do you think there is an under-fueling issue? I do not see it in the SP logs.
RE: Which Cylinders
3 and 7 have the most retard events. However, I am seeing some retard on 6 and 8. There is very little retard activity on 1, 2 and 4.
Here is what the log data looks like now. You can see the knock events in the high load and WOT regions. The engine is running strong and smooth. I think this fuel map was optimized at a 14.7 AFR target and did not have the richer AFR targets in the high load rows.
Here is the revised fuel map with the additive fuel numbers based on the recommended AFR targets for moderate and high loads.
There are fuel increases across the board, with an additional ~10% in the cells with knock events. I am hopeful the additional fuel will reduce some of the knock events. I'll get some log data using this revised map.
Last edited by Michael Benno; 10-03-2023 at 12:19 AM.
Fairly typical.
This does not look like a fuel issue. 12.0-13.0 is plenty rich for a NA engine.
Getting the carbon knocked off of GTS pistons is very difficult. Almost always requires mechanical intervention.
And regardless of what you do, the lack of oil return holes in the oil control rings, ends up pushing the oil into the combustion chamber. (A stock GTS piston is fully skirted.....there's no passageway for the oil to return to the crankcase.....it can only go one way!
Run a colder heat range spark plug (or even two heat ranges colder) in the middle 4 cylinders. (If you are running 7's in Bosch, run 5's.)
#8 probably knocks because the water flow is short circuited from "extra" holes in the head gaskets.
You could put a one heat range colder plug in that cylinder, also.
Try a "6", there.
Finish your 5.0 and use it, while you redesign the GTS engine.....
Good to know that this data looks fairly typical. Thanks for this insight.
Pistons: Yes getting those pistons drilled (and HG replaced) is a top priority and hopefully an end to oil ingestion drama and maybe knock drama too. Plugs: Funny you mention running colder spark plugs on the center 4 pistons. That is what the PO had done. I noted this when I changed the plugs a couple of years ago. I wasn't smart enough to know what the intention was. Cyl8: Interesting notation on the cooling circuit, So Cyl-8 gets a little hotter because of the shortcut holes on the HG.
RE: "Finish your 5.0 and use it, while you redesign the GTS engine....."
Agreed.
The fueling looks optimal to me. Although my 928 is a GTS unfortunately [or fortunately depending on how one looks at it] my motor is the one I removed from my destroyed 90S4 with some mild tuning.
What i found during my ST2 learning curve days was that the motor to some extent is prone to false knock events- i.e the system is picking up noise but seemingly not caused by detonation. Porsche even tell you that detonation events are quite normal and define what is acceptable based on number of knocks per zillion or whatever firing events. To me a true knock event should occur most times the motor hits the specific point of knock but that just does not seem to happen so I would be very careful not to be led up the garden path over what may be nothing.
I have read previously that GTS motors are prone to knocking more than S4/GT motors and that is probably because of the **** awful breather system variants on the stock GTS's. If you have an improved system then that should not be an issue. My motor had a tendency to knock more on cylinders 2 & 6 that I put down to their runners flowing more air at higher rpms. On the other hand I also found that when trying to adjust AFR to control knock it seemingly made no difference and only retardation made a difference. However at full load/high rpms I found that retardation made little difference to the knock count and that led me to suspect that the "knocks" may be nothing more than noise.
Another consideration is the exhaust system- do you have a stock exhaust or one with some degree of customisation to help it flow better [ X pipes/diferent mufflers for instance]? A faster exhaust requires less advance. The stock map for my non cat S4 motor had 27 degrees of advance at full load/high rpms whereas the map for cat equipped models was 29 degrees as I recall. My exhaust system deployed at the time had a Louie X pipe, a large Bullett muffler in the mid section and the RMB instead of the rear box - with that setup I had to pull a little timing to suppress some knocks.
To stroke the GTS Porsche had to revise the piston to make it squatter so maybe that makes the GTS slightly more prone to picking up knocks. For sure Jim has plenty of experience with his GTS. As for the crankcase venting/breathing I understand that to be something of a disaster but no experience of having to deal with such..
Hopefully the chaps can give you far better input than I can.
Fred, thank you for the additional insights. This is very much appreciated. All this feedback is helping to broaden my knowledge and confidence when looking at the data and making decisions on tuning.
Exhaust Mods: Yes, this GTS does have an X-pipe, no cats, and 2.5" free-flowing exhaust with Mangaflow free-flowing mufflers. So I will take your comments of "A faster exhaust requires less advance" into consideration when adjusting timing.
Good to know that this data looks fairly typical. Thanks for this insight.
Pistons: Yes getting those pistons drilled (and HG replaced) is a top priority and hopefully an end to oil ingestion drama and maybe knock drama too. Plugs: Funny you mention running colder spark plugs on the center 4 pistons. That is what the PO had done. I noted this when I changed the plugs a couple of years ago. I wasn't smart enough to know what the intention was. Cyl8: Interesting notation on the cooling circuit, So Cyl-8 gets a little hotter because of the shortcut holes on the HG.
RE: "Finish your 5.0 and use it, while you redesign the GTS engine....."
Agreed.
I missed that you had few knocks on #2 and #6. Go one heat range colder, with those.
Your current oil control system has to be better than stock.
Once it is apart, put in my trick valve cover oil separators, filler neck oil separator and change how the system is plumbed, per my instructions.
Remove the Provent and the vacuum pump.
Drill the oil return holes in the oil control rings and perform piston update # 8806 (Book "E", page 39.)
Note that your 5.0 engine pistons needs this same modification, if the factory did not do it (Very "hit and miss".....one engine guy had no idea what the other guy was doing and KS/Mahle should have had the ***** to tell Porsche that their engineers had their heads up their a$$es.)
BTW....I've seen both standard and 1st oversize S4 pistons with no oil return holes in the oil control rings....you've got to be very observant!
Magically, oil intake/combustion chamber issues become non existent.
Completely different animal.
Fred, thank you for the additional insights. This is very much appreciated. All this feedback is helping to broaden my knowledge and confidence when looking at the data and making decisions on tuning.
Exhaust Mods: Yes, this GTS does have an X-pipe, no cats, and 2.5" free-flowing exhaust with Mangaflow free-flowing mufflers. So I will take your comments of "A faster exhaust requires less advance" into consideration when adjusting timing.
That may well explain what you see. Given your motor was originally cat equipped is your motor still running the cat equipped maps or is it still running the non cat maps as defined by the stock configurqtion plug that tells the brains what it is playing with?
The other point of note is what fuel are you running? Canada uses the AKI system as used in the States and in that parlance you should be running AKI 93 minimum. Shell V-max meets this criteria and is commonly available in the likes of BC and Alberta and doubtless in the other big cities like Toronto and Montreal [never been there yet!]. The stock maps are tuned to 98RON and the theory is that as and when one visits less advanced societies the motor can still run using lower octane numbers by virtue of the retardation mechanism. I was schooled that knock is characterised by audible knocks and whereas I have recorded a few knock events I have never heard any knocks taking place. A dear friend of mine had a brand new GTS and I remember him complaining back around 1996 that his GTS actually knocked "audibly"- we only had 95 RON available at the time. Hence I concluded that the GTS may be "marginal" knock wise. For sure Porsche did not leave a lot on the table tuning wise for their EZK kitted vehicles.
That may well explain what you see. Given your motor was originally cat-equipped is your motor still running the cat-equipped maps or is it still running the non-cat maps as defined by the stock configuration plug that tells the brains what it is playing with?
The other point of note is what fuel are you running? Canada uses the AKI system as used in the States and in that parlance you should be running AKI 93 minimum. Shell V-max meets this criteria and is commonly available in the likes of BC and Alberta and doubtless in the other big cities like Toronto and Montreal [never been there yet!]. The stock maps are tuned to 98RON and the theory is that as and when one visits less advanced societies the motor can still run using lower octane numbers by virtue of the retardation mechanism. I was schooled that knock is characterised by audible knocks and whereas I have recorded a few knock events I have never heard any knocks taking place. A dear friend of mine had a brand new GTS and I remember him complaining back around 1996 that his GTS actually knocked "audibly"- we only had 95 RON available at the time. Hence I concluded that the GTS may be "marginal" knock wise. For sure Porsche did not leave a lot on the table tuning wise for their EZK kitted vehicles.
Hi Fred, great insights! Ignition Map: Yes, this car was originally a Cat car, and I am probably using that ignition map still. I'll need to check and change it. GAS: The gas I am using is 92 octant USA the equivalent of 97RON. So maybe there is something to that angle.
Ken is going to help me with the ignition map later this week. He has a method of pulling back timing for individual cylinders as needed. It's way over my head, so I'll give you more updates afterward.
Hi Fred, great insights! Ignition Map: Yes, this car was originally a Cat car, and I am probably using that ignition map still. I'll need to check and change it. GAS: The gas I am using is 92 octant USA the equivalent of 97RON. So maybe there is something to that angle.
Ken is going to help me with the ignition map later this week. He has a method of pulling back timing for individual cylinders as needed. It's way over my head, so I'll give you more updates afterward.
Maybe it is the same patch Ken wrote for me which was very helpful when I was trying to assess the impact of timing cylinder to cylinder as it were. As a test vehicle it was excellent but it is not a long term solution in that it advances or retards every cell for the given cylinder being tested. I found that by retarding 2 and 6 a couple of degrees I could advance all the others more across the board. - doubtless Ken will fill you in on this.
The other thing you can do is to instruct the brains to override the coding plug and read the non cat map. Ultimately of course the entire point of ST2 is write custom maps to opimise your specific vehicle/configuration. I preferred to tell the system to ignore the full load maps and set the values in the cruise map- ST2 told me the full throttle switch was not working so it was a good work around. I did replace eventually and never felt a need to revert.
I took the car out on my favorite test loop and was able to log some data using the updated fuel map described in post #3. In this test, I was primarily testing WOT so you will see most of the data is at the bottom. The knocks are greatly reduced with the extra fuel.
This is the Ignition Crusie Map for non-cat cars, the the knocks are a little easier on this view, black X's
The knock count was 83 in the previous runs and the retard was across 6 of the 8 pistons. This time knocks are down to 14 and are limited to 3 6, and sometimes 7. And, the amount of retard is greatly reduced from before. Below is a view of the log data filtered for rows with knocks.
This is a huge improvement from before. The motor was pulling extremely strong and the sounds were amazing. Truly addicting.
In reference to my original post, this is where some benchmark data would be helpful. Is the number of these knocks at high load still within the totally normal zone? This seems comparable with what I would see in my S4/5spd.
It will be interesting to see if we can work on further reducing these remaining knocks through ignition manipulation.
Last edited by Michael Benno; 10-05-2023 at 12:41 PM.
Late to the party, apologies-- we just got back from Rennsport. I do have some log data from our 93 GTS, a couple of screen-shots below. I think you are on the right track, additional fuel seems to be more helpful than fiddling with timing. This car was completely stock (except for PEMs and a Sharktuner connected). I haven't gone back and looked carefully at what I changed. The top-end AFR is around 12:1, pretty rich, that was fuel that I added to calm down the retards.
This is the "before" plot, AFR was around 12.7 at the top end, and EZK was busy-- pulling timing from all eight up to 5.3 deg. Lots of retard going on, but not out of range (max retard is 9 deg). And also a cloud of small retards in the 3000-ish RPM range, around max torque and in an area that would normally be closed-loop (i.e. 14.7 AFR).
(Note that this was running LH open-loop-- NBO2 disabled-- so all the dots are large).
This plot is after adding fuel, same ignition timing but AFR at high load is around 12.1 and EZK is much less busy:
(NBO2 sensor was enabled here, so closed-loop in the light-moderate load areas as indicated by small dots. The closed-loop area is delimited by the gray shading).
Much more reasonable, a few cylinders retarded a few degrees at the top end-- which I think is fine, that's EZK doing its job. I haven't looked carefully at the retards per cylinder as you did, but a quick look at the small retards around 3000-ish RPM showed mostly #5 retarded a degree or two.
Hi Jim! Welcome to the party, and thanks for posting up that data from way back in 2013. It is still very relevant. It's reassuring to see both GTSs have similar issues with under-fueling and knock in the similar RPM/Load scenarios. And we both had similar outcomes if less knock and less retard by adding more fuel.
I am curious about the interplay of the flappy since the RPM range of many of the knocks (for both cars) is around the flappy activation zone. I wonder if the flappy changes the airflow in the runners enough to shift the AFR needs in each cylinder.
What are your thoughts on further knock mitigation actions for my particular car? Is it good enough; or try to minimize more? If so please share your thoughts on next steps
10-02-2023, 05:14 PM
Wanted: Sharkplotter data from a GTS
