Is it wrong that I made myself laugh?

I can't believe I can't find someone that would want to come and rag out a 991 GT3 with me. Oh well, someday I'll find a friend that's cool like me.

 

Jim, I don't know how I missed this post. The floors look great! Man I want a four car garage. I'm about a year away from doing plans. I'm limited on how large of another garage I can build, but it's going to be awesome. Probably something like 32' X 26'.

I have some crazy ideas: plumbed compressed air, like a thousand lights in the ceiling, 12' ceilings, inground lift, Lista Cabinets, 20' garage door, 20' porte cochere for washing cars in the shade, home theater, giant murals of my cars, A/C, a hot/cold/deionized/pressure washer built in, etc, etc, etc. Now I just need a few hundred thousand bucks to build it.

 

You need to make yourself laugh, its the only way to get by these days I find

Thanks again for the vids and posts... when is the dyno again?

 

This Friday at 9AM.

 

Matt,

My buddy installed the Big *** Light I told you about... He really likes it and says it puts out a ton of light... I will have to check it out next week.

Looking forward to seeing your new garage when it is finished. You have some good ideas. It is easy to get carried away with something when you have a passion for it.

Speaking of carried away and man caves... I did the home theater room awhile back and have never regretted it... It brings my wife and I a lot of enjoyment on a weekly basis...

 

Waiting anxiously for your dyno numbers!

 

Alright my friends, I took one for the team. I left the valves disconnected for a week to be sure I wanted to even perform this test. Believe it or not, the car drones quite a bit less with the Sharkwerks Bypass than with the OEM 3rd Muffler and the valves disconnected. So I decided I will keep it if I don't lose a bunch of low-end power.

So I got up bright early, blew off the office, drove an hour and fifteen to Orlando, and ponied up a couple of hundred bucks to test out my free mod.










First off, let me tell you how awesome Titan Motorsports is. I had been there about 13 years ago to have my VTEC controller dialed in on my AP1 S2000. They are now in a different mega location and have one of the best DynoJet set-ups in the SouthEast.






I thought I had read somewhere that the front wheels need to be rolling otherwise the ECU would start kicking and screaming. They have not only the four wheel dyno, but the proper connecter to allow the front rollers to move in tandem with the rear. We are guessing there is a bit more loss from the car having to move the front rollers as well, but I didn't care about max power output. I just want to be able to compare back-to-back-to-back... runs.









I got there super early as I always do with everything in my life and met a Brazilian importer/exporter that was shipping a Veyron replicata body to be used for TV shows. He hadn't seen a 991 GT3 as they cost about $400K in his country. We had fun chatting about different cars, etc.





When Titan actually opened, I went in to introduce myself. The shop manager met me and emphatically stated to "make myself at home." Now most shops don't allow you to leave waiting room. He made an announcement that I was free to roam. I thought, this is going to be fun. These guys build world class mega HP Supras. As you might imagine, there was some cool stuff sitting around the shop.
























Since I was there so early and they were working on fixing an Evo's full pump tying up the dyno, I took the opportunity to play around with my new 24-70mm f2.8L II lens. I took some shots of my car around the shop just for fun.





















Then it was my turn to get on the Dyno. I usually get a little nervous when putting my car on a Dyno. I've done it about a half a dozen times with various cars. This is by-far the most expensive car I've ever owned so by default I had the most to lose should the car shoot off the platform at 9K. For some reason, I didn't even think about it. These guys knew what they were doing. I felt very at ease.




















They quickly got it loaded, found the coil pack, and had it ready to test. This is the first 991 GT3 that most anyone has had on the dyno, but it didn't take them long to get it dialed in. I only had to explain what I wanted done once. It was awesome. Normally I'm wondering anxiously if I'm going to get anything close to done right when I go to some shops. It's probably why I prefer to do everything that I can myself. Not this time, it couldn't have gone any smoother. Here is what I wanted to do:





PSE OFF Connected Valves at Moderate Throttle in 3rd Gear from 2-5K
PSE ON Connected Valves at Moderate Throttle in 3rd Gear from 2-5K
PSE OFF Connected Valves WOT in 4th Gear to Redline
PSE ON Connected Valves WOT in 4th Gear to Redline

PSE OFF Disconnected Valves at Moderate Throttle in 3rd Gear from 2-5K
PSE ON Disconnected Valves at Moderate Throttle in 3rd Gear from 2-5K
PSE OFF Disconnected Valves WOT in 4th Gear to Redline
PSE ON Disconnected Valves WOT in 4th Gear to Redline

I wanted to test to see if the Sport Exhaust Button would still be necessary to press despite the fact that the Vacuum lines are disconnected. I wondered if the button actually changed anything in fuel maps or timing or something else that I didn't even know existed.

But the main reason for the test is to see if there is a measurable amount of loss when disconnecting the valves, forcing them to be open at all RPMs. It has been theorized by many that Porsche designed the exhaust this way to ensure proper back pressure to maximize drive ability while also reducing drone. I wondered if possibly it is done only to meet a certain sound profile.

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.




Run 2:
PSE ON Connected Valves at Moderate Throttle in 3rd Gear from 2-5K
This shocked me a bit. It leads me to believe there is something more to the PSE button of than just the valves opening. Notice how much flatter the curves are. Remember the valve are still opening around the same RPM, yet we don't see a rather linear curve.





Run 3:
PSE OFF Connected Valves WOT in 4th Gear to Redline
This confirms the weird dip with PSE deactivated and valves connected in the previous Run 1. Take not that there is a bit of noise in the torque curve throwing off the Max Torque. It is actually closer to 260 ft-lb.




Run 4:
PSE ON Connected Valves WOT in 4th Gear to Redline
Again confirms our previous runs. Notice the smooth transition at lower RPMs even at Wide-Open-Throttle. Leads me to believe there is some timing, etc. being adjusted by the ECU by depressing the PSE button. The valves still opened around 3,700ish RPMs. Maybe a bit sooner at WOT.





Now we disconnected the valves to do some comparison runs. This would either dispel or confirm the rumors that Porsche engineers designed the valving system they way they did to maximize power and sound. Well, the problem for me is that I hate the sound of the constant switching from open to closed. FYI, Run 5 was no good. So we start at 6.

Run 6:
PSE OFF Disconnected Valves at Moderate Throttle in 3rd Gear from 2-5K
Good news! No dip in power. We actually see an increase with the PSE button deactivated and the valves disconnected!





You can see the comparison of Run 1 connected vs. Run 6 disconnected both with PSE off.





Run 7:
PSE ON Disconnected Valves at Moderate Throttle in 3rd Gear from 2-5K
Other than starting to sample the data a little earlier, it is nearly identical to Run 2. So I guess the PSE button isn't doing anything else?




Once again, we did get more power with the valves disconnected and the PSE button On.





Run 8:
PSE OFF Disconnected Valves WOT in 4th Gear to Redline
Same results under WOT to Redline.




Much more linear/flatter curves. There is also a bit of a top-end HP increase that is confirmed by Run 9. Maybe due to inertia built at the low-end?






Run 9:
PSE ON Disconnected Valves WOT in 4th Gear to Redline
Nice and smooth/flat!












HERE IS THE VIDEO:

991 GT3 Exhaust Valve Dyno Study - YouTube

Correct me if I'm wrong, but the conclusion here is that Porsche simply makes the valves open and close for sound rather than back pressure/power maximization. Granted I do have a third muffler delete, but I would guess the results would be the same.

I failed to have Titan do comparison graphs of the PSE Button ON/OFF but I think you can still draw conclusions. Maybe some smarter than me could explain why there is a noticeable difference in power output by with the PSE Button ON and the Valves Connected? The Valves are still closed at low RPM with the PSE button activated. Why are the curves more linear and flatter in Run 2?

I hope this is helpful. Thanks for reading.

Matt

 

Awesome data collected, thanks a lot. I'm sure that other 991 GT3 owners will really appreciate this effort too.

 

Matt -

Thanks for stopping by today and bringing your beautiful GT3! I've enjoyed reading this thread (and seeing that this car went to a great home after Nero dropped the ball lol). Glad we could help with your testing, however I really picked the wrong day to have a lunch meeting as I didn't get to hear the car on the roller in person, the good news is we should have our very own 991 at the shop on Monday and even with all the great cars we've got in the shop, it's the one that has me the most excited (but I'm probably a bit biased on that one). Enjoy the car, let us know if there is anything else we can do for you, and we hope to see you on March 7th for our annual open house, VIP parking up front if you're able to make it out!


We couldn't resist making our own video of your beautiful GT3, hope you enjoy!

-Wes

 

So Sick Wes! I love it. Too bad 991 GT3 are so slow by making a weak 380 whp. I'm guessing the link to get the front wheels moving is creating another drivetrain loss factor.

I'll be taking you up on that "VIP" spot in March!

 

Love that video by Titan...great stuff there.

 

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)

 

Just when i didn't think the thread could get any better!
Simply Wow!
Amazing footage and comparison of the dyno test runs.
Thanks for taking the time to put together and share.

 

Look into the Canon 70D, it has autofocus in video mode. Awesome thread bro.

 

Thank you for the detailed thread! I love your updates.

Quick question: do you know how many gallons the extended range fuel tank has? I believe the regular 991 fuel tank is 64 liters (16.9 gallons).