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My comment refers to my experience with measuring NA cars on the Dyno. I always end up measuring less than I'm hoping/guessing I will make.
You must have missed the comment that a RWD 991 911 won't work on a rear-wheel only dyno. If the front wheels aren't moving, the car goes limp.
Yah I did miss that about the ECM, but that obviously makes the car nearly impossible to accurately chassis dyno and explains the results. disappointing numbers in general to say the least and obviously not accurate in relation to real world performance---thats all I am saying has nothing to do with you at all.
I wonder if there is a way for the tuners to disconnect front wheel speed sensors
and thus get a much more accurate result?
What an awesome post. Thanks for taking the time to provide such a thorough analysis. Can't wait to get my SW bypass installed and to disconnect those valves.
Well done Money
I too hate the sound variation from a throaty idle sound to a flat between 1-3.5-4k rpm. I'm seriously considering disconnecting the valves as well especially that on occasion I wonder if the PSE engages or not.
However I have a question: I love the pop of the exhaust at shifting in higher rpm (past 4k). It that totally eliminated when the valves are disconnected?
Well done Money
I too hate the sound variation from a throaty idle sound to a flat between 1-3.5-4k rpm. I'm seriously considering disconnecting the valves as well especially that on occasion I wonder if the PSE engages or not.
However I have a question: I love the pop of the exhaust at shifting in higher rpm (past 4k). It that totally eliminated when the valves are disconnected?
You will retain that snap/pop when aggressively shifting/driving.
Run 1: PSE OFF Connected Valves at Moderate Throttle in 3rd Gear from 2-5K
I wanted to simulate a typical driving environment while on the dyno. So we did a basic third gear rolling 2,000 to 5,000 RPM pull under normal moderate throttle. The result is a very noticeable dip in both HP and TQ leading up to the valves being electronically opened around 3,700 RPMs.
Matt,
Thank you for doing this. I've been waiting to see what results followed because I have a SW bypass and was told I should keep it off due to Porsche's concern that there is insufficient back pressure with third party exhaust and an inference that installing it could damage the engine. So, I plan to keep it off during break in and wait until after max power is supposed to be achieved after 10k miles per Andreas P as I've read in some thread or another.
I would prefer a linear exhaust note through-out the power band sounding like OEM after 3,700 RPM with PSE on instead of the tamer sounds with PSE off or with PSE on and RPM under 3,700. So, my first question is whether that will be achieved with valves disconnected and PSE button always depressed on? Is the best chance of having this sound take place with SW bypass installed, valves disconnected and PSE on? Will pressing PSE matter with SW installed and valves disconnected? These are my questions.
But, the biggest question relates to the above quote and chart. It seems to be the only chart that shows power loss. I wonder whether this is a fluke, one of a kind result or accurate and if something is going on that Porsche knows about but, still has the valve setting in place for a reason despite the power loss by having these valves. And, the question for that chart is, whether Porsche intentionally reduced horse power when PSE is off. OEM settings would be valves connected and I'd like to know if messing with those settings by disconnecting valves and adding SW, or any other after market exhaust for that matter, will create a problem with Porsche's OEM settings. With valves disconnected, that dip in power before 3,700 doesn't exist. In theory, peak performance is achieved by disconnecting the valves.
My thought is, the answer to these questions as to peak performance and linear sound is to disconnect valves, add aftermarket exhaust, in my case the SW, keep PSE on (not sure how this would matter with valves disconnected other than perhaps ECU related changes for something unknown such as timing, air or fuel flow etc.). And, that the only remaining question is whether doing so will somehow harm the car. My guess is probably not. But, then I ask, why would Porsche technicians press for me to not mess with stock settings by adding the SW bypass. I was told "there is a lot going on at 3,700 when the sound changes with PSE on." They obviously know something I don't and perhaps something not being discussed on the forums. I'm not inclined to simply ignore the opinions of my dealership technicians who have received Porsche training, especially on such an expensive vehicle, during warranty and therefore, I have left off the SW bypass and am debating whether or not to install it at all. Responses to my questions will likely affect how I proceed.
Thanks again for getting these results Matt. If you or anyone else has any answers to these questions and thoughts, I'd appreciate further comment or response.
I wouldn't get too caught up in the actual numbers until you can compare another car on that same dyno. Dynojet, Mustang, Dynapaks & Dyno Dynamics can all be calibrated by the end user, so it is a complete waste of time trying to compare from different shops.
I watched a stage 1 tuned 996tt put down 327 whp on a Mustang. Owner was really disappointed when my Subaru STI put down 330.........until I showed him what was under the hood! Both cars would be around 480-500 at the crank, so they were a decent comparison.
They are great for seeing results of performance mods as well as studies like the exhaust valves. The key is the before and after on the same dyno, same day as atmospheric conditions can alter the results. What is a complete waste of time, is comparing numbers from different dynos.
I'm sure Titan has a dyno plot somewhere of a car close to the GT3 power. That would give you a better idea as long as temp and humidity were similar for both tests.
Do you guys think that the results would be the same with the original factory exhaust ?
Good question. Yes.... maybe.... who knows? It's another variable that we can only make assumptions about.
As others have just posted there is a lot of complexity around dyno testing, tuning, and the effects of making changes to a stock configuration that has undergone thousands of hours of development by the manufacturer. Without the same resources and a certain knowledge of everything that's been engineered into a system, it's hard to know exactly what effects a change will have under all conditions.
This is what Wes from Titan posted in my 6speedonline Journal:
"Correct, the vast majority of AWD dynos out there have 2 sets of rollers, but they're spinning at different speeds (which is fine since most cars don't use a 50/50 power bias front to rear). The rear roller gets most of the power and gets the reading, the front spins just to keep the front diff happy ( a car not happy with this setup will let you know typically with the front differential getting very hot from the diff overworking itself and in some cases even failure. A number of years ago during our move we had our 996tt dynoed at another local shop, needless to say they forgot to link the rollers and we ended up having to find a replacement front differential in quick time!
More modern cars like those from BMW / Porsche / Audi , etc require that the front wheels spin at the exact speed as the rear wheels to keep the traction control and other systems happy. The Link solves this problem by using a massive belt and tensioner to connect the rollers so that they spin at an equal speed. The downside to this is that the car is now not just spinning the rear rollers, but it's power also helps drive the belt that spins the front wheels at a significant load as well. The result is more driveline loss and lower "percieved" number on the screen as it will be no where even close to the manufactures states crank HP numbers (typically 15% on one roller with a manual transmission is common, in this case 20-25% probably isn't out of the question) "
But, then I ask, why would Porsche technicians press for me to not mess with stock settings by adding the SW bypass. I was told "there is a lot going on at 3,700 when the sound changes with PSE on." They obviously know something I don't and perhaps something not being discussed on the forums.
Dan
Were you actually told this by the folks at Rusnak? This is surprising since most Porsche dealers are ok with SW and still honor the OEM warranty.
Good question. Yes.... maybe.... who knows? It's another variable that we can only make assumptions about.
As others have just posted there is a lot of complexity around dyno testing, tuning, and the effects of making changes to a stock configuration that has undergone thousands of hours of development by the manufacturer. Without the same resources and a certain knowledge of everything that's been engineered into a system, it's hard to know exactly what effects a change will have under all conditions.
The beauty of testing... answers a few questions, but usually raises more questions
12-20-2014, 08:31 AM
