Money2536

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 someone 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

MileHigh911

Great video and many thanks for the testing!!!!!! Very interesting indeed!!!!

bigkraig

thanks!

hughp3

Thanks for the work here! More concerning is a 100 hp drop. Drive train I thought should be 15% or so? Well if it will still do the qtr at 126mph as advertised who am i to care...

vic55

As thorough as possible Matt---- thanks for taking up your time today for this excellent real world data.

Conekilr

Fantastic Matt, thank you for doing this. You are the Man !!

Love the nice flat torque curves with the PSE on !!

BTW, you make the best exhaust videos ever !!

911dev

Deleted

alaint101

This is awesome.

It just so happens that I was at the dealer today for an unrelated question. (Paint / see other thread started by Dark Knight)

I asked the techs if there were any concerns associated w/ disconnecting the valves.

Their answer: "no". It should not harm anything.

So I will be getting 'disconnected'...

MaxLTV

I'm too lazy to think for myself now, so can someone tell me if the graphs would be the same for PSE on and off if the valves are disconnected.

Conekilr

Yes, that seems to be the conclusion.

SamFromTX

Awesome. I always believed the reason was sound not low end torque, especially in a car that revs high to do its purpose. Fantastic fact filled post.

frankee4u

Brilliant - thanks

Lodi

Thanks Money! Really appreciate the time, effort and expense. Good to know the facts.

Gravs

Best post ever!

Am I right in thinking the valves open a hole in the exhaust between the side mufflers and the centre muffler? I.e. one hole on each side?

Or do they restrict the pipe when closed?

If the former then we could expect greater gains still if the centre muffler has not been deleted.

Mike in CA

Fascinating Matt. and thanks so much for the effort and thoroughness.

I was particularly interested in the 2 plots shown below; the part throttle-PSE on-valves connected (runfile 2) and the part throttle-PSE on-valves disconnected(runfile 7). Runfile 2 actually shows slightly higher peak HP (226 vs 218) and fractionally higher torque (227.94 versus 227.02) with the valves connected. A difference in peak rpm between those two tests?

Regardless, there doesn't seem to be the torque dip that my butt dyno detetected; perhaps it needs a calibration. You mentioned at the top of your post about the drone with the stock center muffler and the valves disconnected. I think the character of the sound with my stock system may have been misleading me; a lot more noise with disconnected valves but no real difference in performance tricked me into feeling that torque was degraded.

Bottom line, I won't disconnect the valves again as I prefer the stock sound, but at least it's good to know that there appears to be no performance penalty for those who want to do the mod. Thanks again for providing some clarity to all of this.