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Sticky, I have been involved in many STI/EVO builds and still have a Cosworth long block in a STI which makes over 500HP without restrictors .
Thus, I know enough about dynos (thats why I understand that top end MAHA dynos electronically control front and rear wheel speeds to match and thus not trip the car electronics e.g. Porsche PDK) and thus (over here) I would only uses MAHA (MSR500/1000/1050) or hub dynos (Dynapack) if I wanted consistent results. This is no longer relevant to me as I'm no longer involved in that form of "hobby".
I have a pretty good understanding of this stuff - the fundamental problem with dynos is without the supporting information, corrections, smoothing through to engine hours, tire condition or even airflow measurements the numbers produced are often at best a good approximation.
Comparisons between results from different dynos, in different locations under different conditions at different times is fraught with misinterpretation (as you know). According to just about every forum, all Porsche cars are massively under rated - they are not, you only have to look at the paperwork that comes with crate replacement engines - they have the rated HP and torque stamped on the box for that specific engine.
Hence my question to you - was there a correction applied to your run with your 991.2 and directed you to the very good article by Sport Auto - on the effect of double dipping (I think it was released Jan 2016). In a nutshell, they concluded that with current generation turbocharged cars its a mistake to apply certain corrections. The result being an over estimation of 40 to 47HP (with respect to the TTS they tested).
I'll try and find the article for you
If you have dyno'd various cars then I'm surprised you don't know different dynos vary.
I have no doubt the MAHA is a great dyno and I only hear good things about it. That said, I don't have a MAHA available to me and there are US companies that produce dyno machines that are just as good if not better.
The main thing for a useful comparison is to have the same cars on the same dyno. That is why this overlay is useful, right?
The cars are using the same dyno. It is no different from my car using a Mustang and comparing against cars on the same Mustang.
The 991.2 base, S, or GTS is always making its same horsepower whether it is dyno'd in Europe on a MAHA, Australia on a Dyno Dynamics, or in the USA on a Dynojet. It is only how the output is calculated by the dyno that varies so you will get different numbers.
You are quite correct regarding the wheel speed sensor issue. This is why I could not dyno on a RWD Dynojet despite preferring this dyno due to it being the most popular and IMO the most useful for context.
I used a Mustang which is all wheel drive and that is why you see many US dyno's on Mustangs for 991.2's.
I did not have any special correction applied although obviously you can mess with a dyno to change the numbers. This is also why other 991.2 C2's are matching my baseline. I believe this article on the topic will inform you greatly as to where I'm coming from and the differences in dyno types: http://www.****************/content.p...an-vary-wildly
To be honest, I'm not sure what your argument even is or what you are questioning or trying to say regarding dynos. I'm pointing out that a 368 whp rating for a 991.2 GTS is very conservative and that to have useful data you need to compare on the same dyno type and understand the differences in dyno types. I'm also pointing out the 991.2 base car is underrated by Porsche. The dynos AND 1/4 mile times all support this exactly as they should.
I'm not really sure what your point ultimately is here but if you read the article I linked about how Mustang and Dynojets vary and how dyno numbers can vary I think you'll understand my position better as well as have a better understanding of getting useful data from a dyno.
Team - Dyno's are pretty worthless to compare different cars - on different dynos (even if they are the same make/model) on different days in different environments.
For example - a highly boosted engine can have a spread of 100hp over a similarly specced HP NA engine if you go to high altitudes.
Dynos are tools to measure and benchmark on the same car to determine before/after changes and to get a baseline tune.
Comparing cars' dyno results is dumb. Any internet warrior can get the shop to manipulate the corrections to show whatever number they want... I know on here we're all above that but it is a sticky situation we can get ourselves in. Everyone believes their shop knows what they are doing... many tuners learn as they go and many don't know how to do corrections properly on boosted cars. Again - surely anyone that any individual uses would surely be a wizard and know everything but just be open to this not being the case. At the end of the day it doesn't matter. When people have to go here it's because they don't love their cars enough and need to make it something they are not.
This person does not understand how dyno's relate to 1/4 mile times or why certain dynos are popular for tuners. For example, eddy current load bearing dynos which can simulate various road conditions.
Additionally, due to varying elevations and weather conditions is why we have correction factors like STD and SAE. This person clearly does not have experience with these correction factors:
SAE Correction
SAE J1349 is the current gold standard of dyno testing and represents the newest widely accepted industry standard correction factor. Reengineered in 1990 (yeah, a long time ago), the SAE correction factor standardizes temperature to 77-degrees F, 29.23inHg and dry, 0-percent humid air.
If you have a good understanding of various dyno types and experience with results on said dynos you can compare results to get an idea of what kind of power the car is really making.
You ultimately want to focus on the delta and use the same dyno type to remove variables but as the MAHA dyno shows it is not always possible to get everyone to use the same dyno as different regions have different machines available.
If someone thinks people who aren't selling anything but just testing their car are manipulating their results for some unknown reason they are not interested in the truth or independent testing but solely in negative arguments for the sake of said argument.
The best thing to do? Go test your car on your own and see what it puts down. If numbers are being played with it will be very easy to call it out with evidence. Compare it to other cars and other runs. That, or type. One of these is more useful for owners wanting to get real info on their car than the other.
Boost level is what gives the Hp. Smaller turbos just have to spin faster to make 16 psi than does a larger turbo.
base running roughly 16.5 psi should make 430 Hp ( base plus 60 hp)...... just like the S makes 420 at 16 psi.
Exactly but also remember boost pressure and output is not going to be equal among different sized turbochargers.
There are also different points of diminishing returns although you mention this.
The base and S won't see a huge difference as the S only has 2 mm larger compressor but same size turbine.
The GTS/X51 is where things get really interesting as the compressor is 4mm larger than the S and the turbine is 3mm larger. In theory, the GTS should hit higher peak horsepower than the other two well before being pushed out of its efficiency range.
I hear a hybrid option is coming that will really open some eyes...
Also, this run was completed when it wasn't optimal turbo weather out
Now that it's getting cooler at night here in FL, I'll be heading to the track again and will see what time/trap speed is possible
Exactly but also remember boost pressure and output is not going to be equal among different sized turbochargers.
The base and S won't see a huge different as the S only has 2 mm larger compressor but same size turbine.
The GTS/X51 is where things get really interesting as the compressor is 4mm larger than the S and the turbine is 3mm larger. In theory, the GTS should hit higher peak horsepower than the other two well before being pushed out of its efficiency range.
I agree that the larger GTS turbocharger can acheive higher boost levels.
What is interesting is that the smaller turbocharger has less turbo lag (you can see that in the Suncoast parts dyno chart comparison), but Porsche chose to use a larger turbocharger to achieve 450 hp. Is this because the added heat generated by the smaller turbo ( at the same psi level) would effect the intercooler capacity ( or just politics of selling upgrade differences to the customer)?
If you read the above article you will see that it came about due to the fact Sport Auto ran a 991 TTS and got a very high result which they published - 607HP (instead of 560HP).
They took a lot of heat for this and re-ran the car on three MAHA dynos in three different locations.
They were advised not to apply correction factors e.g. EU80/1269. They got the following results:
MAHA1
Crank HP - 567hp @ 6340rpm (wheel plus towing losses)
Crank TQ - 764.8NM @ 2770rpm
As you can see the results are now as expected - since this article Sport Auto have not used correction factors on new gen turbocharged cars (as opposed to NA cars). The outcome seems to be very consistent results for the Porsche sports cars that have been tested e.g. 991.2 GTS 454HP (crank) and 560NM (crank).
I suspect if you subtract 47HP from your mustang result you will be close to the mark (I am not doubting the data or the intent, just the accuracy).
If you read the above article you will see that it came about due to the fact Sport Auto ran a 991 TTS and got a very high result which they published - 607HP (instead of 560HP).
They took a lot of heat for this and re-ran the car on three MAHA dynos in three different locations.
They were advised not to apply correction factors e.g. EU80/1269. They got the following results:
MAHA1
Crank HP - 567hp @ 6340rpm (wheel plus towing losses)
Crank TQ - 764.8NM @ 2770rpm
As you can see the results are now as expected - since this article Sport Auto have not used correction factors on new gen turbocharged cars (as opposed to NA cars). The outcome seems to be very consistent results for the Porsche sports cars that have been tested e.g. 991.2 GTS 454HP (crank) and 560NM (crank).
I suspect if you subtract 47HP from your mustang result you will be close to the mark (I am not doubting the data or the intent, just the accuracy).
Ok? I don't see what this has to do with anything I wrote though. Did you read the article I linked you to?
What accuracy issue is there? Why would I want to subtract 47 hp from my Mustang result? Maybe the MAHA should add whp to be closer to a Mustang? See the issue? I don't know why you are so single mindedly focused on the MAHA.
Two different 991.2 bases on two different Mustang dyno's both put down roughly the same baseline. The same thing essentially as what you just highlighted with the 991.1 Turbo S testing on different MAHA machines.
So what is the issue or what are you trying to highlight?
I agree that the larger GTS turbocharger can acheive higher boost levels.
What is interesting is that the smaller turbocharger has less turbo lag (you can see that in the Suncoast parts dyno chart comparison), but Porsche chose to use a larger turbocharger to achieve 450 hp. Is this because the added heat generated by the smaller turbo ( at the same psi level) would effect the intercooler capacity ( or just politics of selling upgrade differences to the customer)?
Absolutely according to Porsche's own graphs the GTS has more lag and it simply makes sense of course based on the wheel sizes.
The GTS turbos and base turbos being spun hard enough to make 450 hp would result in much more heat from the base as you highlighted. The intercoolers are the same across the board for the 3.0.
Porsche goes to the larger turbos for efficiency at that hp level but also to give headroom. The base at 20 psi will not match a GTS which can go past 20 psi and still not generate as much heat although there will be diminishing returns eventually as well. Essentially, the GTS has more room to be pushed.
I'm wondering if the X51 turbos do not fall off as much past 7k rpm which would certainly make winding it out to redline more enjoyable. Really looking forward to some independent dyno tests.
The spool on the 991.2 base is incredible. I'll sacrifice a little lag for more top end punch though.
Here is a dyno on the TechArt piggy back using the 991.2 GTS setup.
Compared to the std setup ( see Suncoast graphs) the piggy torque
is slower to rise below 2500 rpm, but increases to 630 Nm instead to the limited 550Nm of the stock setup. The torque does not drop as fast at the high end and thus prduces improved power in both the midrange and the high end ( which has less dropoff when approaching the cut-off.
10-30-2017, 11:42 PM
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