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This might be a good way to represent what is going on. This is a part of a datalog from my Stage 4 running 24PSI of boost on race fuel, ambient temp around 100F, at idle IATs go up to 140F before getting into the circuit. This is the short configuration of the circuit so speeds are below 160mph usually.
From the datalogs and using air mass readings from the ECM, I extrapolated the real engine HP that the car is putting based real life on Lamda, BSFC and air mass, an 8 second dyno will obviously give you higher readings. This is probably the most accurate way to estimate what your engine's output really is especially comparing between maps or fuel etc..
You will notice that in a 10 minute run, the peak top speed and HP have barely changed lap after lap, even with IAT fluctuating up and down from 110 up to 160F, consistent performance. I could show boost levels or any other parameters on this graph directly from the Cobb data. Very few data points with timing pull, this was a fine tuned map.
The graph is somewhat cluttered I tried to show as much as possible. This is a >10 minute run in hot temps. Both the speed (black line) and IATs (red line) are matched to the right hand scale.
Jean, very interesting. As you said very little drop. What formula did you use to establish whp? I see that you data logged the whole session. I was only doing certain sectors. this makes much more sense specially trying to establish differences between initial part of a session and the end.
Just curious, where you doing a cool down lap every other lap?
Would love to have a pure stock 991.2 TTS on the same track, same time, same day with this data log. Stock tune and stock Intercoolers. My tiny bit of log data would suggest pure stock would not be too bad either, although at a much lower hp/heat output.
Great post.
Onfire, unfortunately I do not know anyone with a stock 991.2TT around me.. But logs from a stock 991.2TT on any circuit can be quickly checked the same way. I will be happy to do it for anyone who would like to share Cobb logs. Thanks.
Originally Posted by Pdtp#16
Jean, very interesting. As you said very little drop. What formula did you use to establish whp? I see that you data logged the whole session. I was only doing certain sectors. this makes much more sense specially trying to establish differences between initial part of a session and the end.
Just curious, where you doing a cool down lap every other lap?
I start the Cobb datalogging while in the pits ready to get out and keep it on all the time. Not sure if there was a cool down lap here, I need to check the GPS logger.
Required Airflow= Power x BSFC x AFR/60
=> Power = Airflow / BSFC X AFR/60
Airflow readings from Cobb are in mg/stroke so they need to be converted to g/s or lbs/mn.
Some unit conversions are needed to make all these formulas work together.
Fuel flow = BSFC / FWHP
I use BSFC= ~0.5 on the 991 turbo and 0.47 with meth, this is based on engine dyno logs I have, I have no interest in max.HP usually, I rather look at trends across laps and area under the curve so the exact reading does not really matter for me.
I built a spreadsheet that makes all of this easier and use it on any Cobb datalogs.
Reviving an old thread, might be of interest to some..
Data from GT2RS with Sam/M-engineering tune and cats, stock everything else. On the race track, ambient temp ~120F at the intake. Quite hot and humid day.
Results:
IAT min-max fluctuation GT2RS: Between 120-150F = 30F
IAT min-max fluctuation 991TT: Between 110-160F = 50F
Speed from 80-150mph: GT2RS faster by 1 second +
Barely any timing pull on the GT2RS.
Barely any timing pull on the 991TT
You can see how efficient the GT2RS setup and intercooler are, at full load with a tune temps only fluctuate 30F. In a drag style 1/2 mile run, this would be even less.
991TT was on meth, stage 4, larger IC, intercooler water spray, modified VTG.
Both running almost similar boost levels.
Picture below from the GT2RS. Post #30 above shows the 991TT data.
Question is: Would I need a PWR or an after market intercooler for the GT2RS? I don't think so. Unless someone has better factual data using one of the aftermarket intercoolers on the race track.
But most importantly, having a good tune. This was not an off-the-shelf tune, it took quite some analysis and files back and forth to get a good tune where timing pull is negligeable, fuel, AFRs, ST fuel trims etc.. all in excellent shape. Didn't even get tuned on a dyno. Tune can be pushed further, but keeping heat in check makes you faster on a race track.
Reviving an old thread, might be of interest to some..
Data from GT2RS with Sam/M-engineering tune and cats, stock everything else. On the race track, ambient temp ~120F at the intake. Quite hot and humid day.
Results:
IAT min-max fluctuation GT2RS: Between 120-150F = 30F
IAT min-max fluctuation 991TT: Between 110-160F = 50F
Speed from 80-150mph: GT2RS faster by 1 second +
Barely any timing pull on the GT2RS.
Barely any timing pull on the 991TT
You can see how efficient the GT2RS setup and intercooler are, at full load with a tune temps only fluctuate 30F. In a drag style 1/2 mile run, this would be even less.
991TT was on meth, stage 4, larger IC, intercooler water spray, modified VTG.
Both running almost similar boost levels.
Picture below from the GT2RS. Post #30 above shows the 991TT data.
Question is: Would I need a PWR or an after market intercooler for the GT2RS? I don't think so. Unless someone has better factual data using one of the aftermarket intercoolers on the race track.
But most importantly, having a good tune. This was not an off-the-shelf tune, it took quite some analysis and files back and forth to get a good tune where timing pull is negligeable, fuel, AFRs, ST fuel trims etc.. all in excellent shape. Didn't even get tuned on a dyno. Tune can be pushed further, but keeping heat in check makes you faster on a race track.
Outstanding data. Thanks Jean. GT2RS was very well engineered. Interesting that it was quicker than a Stage 4 with just a tune. Do you have 60-130mph for the GT2RS vs the Stage 4 ?
Correction.. GT2RS is 0.3s slower than the 991TT from 80-150mph.. I was comparing wrong logs.
However the GT2RS has on it a custom racing high downforce package, so much more drag at high speed than a stock one. None of my maps on both cars are maximized for straightline runs or targeting 60-130mph.
My fastest 60-130 on the 991TT was around 5.8s if I recall correctly.
Correction.. GT2RS is 0.3s slower than the 991TT from 80-150mph.. I was comparing wrong logs.
However the GT2RS has on it a custom racing high downforce package, so much more drag at high speed than a stock one. None of my maps on both cars are maximized for straightline runs or targeting 60-130mph.
My fastest 60-130 on the 991TT was around 5.8s if I recall correctly.
You just stopped my junk yard search for GT2RS manifolds and Turbos.....Hahaha. Both of your cars are flying. Well done !
10-21-2019, 10:46 AM
