ElectricChair

997.2 C2 PDK (non-PSE)

I already order the fabspeed x-pipes to pair with gundo hack.

Questions:

1) Should I do gundo with 1.75" or 2" pipes?

2) What's the difference in sound and volume?

Thanks in advance!

WantA997

Just curious why you went with Fabspeed over Sharkwerks (or even Billy Boat)?

ElectricChair

A few posts/threads that helped with my decision:
https://rennlist.com/forums/997-foru...l#post10397993
https://rennlist.com/forums/parts-ma...l#post11475042
https://rennlist.com/forums/997-foru...l#post13073675
http://www.6speedonline.com/forums/9...er-bypass.html

Also a few rennlisters reported drone and vibrations with sharkwerks on 997.2 PDK cars (note = PDK cars only). Asking around before taking my decision, I got this PM from a fellow rennlist member:
"Just an FYI, I had a Shark works Cross pipe shipped and I installed it to my PDK car. I had to remove the cross pipe due to vibration at idle. ( I think it dropped my revs a little causing the vibration ) bad enough that the inside of the car, seats including were shaking."

Sharkwerks added a note to their product page:
http://www.sharkwerks.com/products.php?pid=193
Note: A small percentage of owners have reported that there is a slight vibration at idle speed in Drive (PDK models only), when the brake pedal is depressed at a stop. This has been reported with all aftermarket exhaust systems. This can be fixed with a software tuning upgrade. It is considered normal and will not harm the vehicle.

My understanding is that droning and vibrations can occur with any exhaust mod. But since I am doing a DIY project, I chose the "less risky" road.

kruzn911

very interested in the same setup as you. Looking forward to hearing some sound clips!

Crester

I have the set up you are going for... Fabspeed and Gundo. I went with 2" and I think you should as well. The car isn't that much louder when driving normally. It's only when you are heavy on the throttle that the car gets loud.

I also choose Fabspeed over Sharkwerks because of the vibration issue on PDK cars. I don't have any vibrations when stopped... but the Fabspeed makes your engine sound more high pitched. It's upto you if that's a good or bad thing.

Iceter

I'll chime in here and say first that this is only my opinion and I have NOT heard two cars side by side with a 1.75" versus 2" Gundo hack.

That being said, IMO, there will be zero difference between the two.

I say this because:
1. The hack is a straight pipe that acts as more of a pressure equalizer than an exhaust diverter.
2. The difference in the volume of any flow down the pipe is minimal between 1.75" and 2".
3. The hack is buried several feet upstream of the exhaust outlet, minimizing any effect that a very slight change in pipe diameter at the hack would cause.

If anyone has audio of the two pipe diameters to compare, I'd love to hear it, but I think this is something that doesn't really matter very much.

The only question I've ever had about making the hack more effective is this... . I'd love to weld in a curved pipe in place of the straight hack, so that much more exhaust flow is diverted through the hack and away from the muffler. I've always thought that the exhaust probably had enough velocity that most of the flow just bypassed the hack tube and shot straight into the muffler. I've wondered if a contoured hack pipe would not only change the sound but actually improve performance--even if just a little.

jhbrennan

Do we know what diameter Fister uses?

docdrs

Its quite simple..... its 2-1.75 / 2 or 12.5% quieter with the 1.75 diameter pipe over the 2" pipe. Do the 2" and if its too loud pinch the pipe to reduce the blow by volume.

ElectricChair

Fister uses 1.75".

ElectricChair

Interesting idea. That would be very loud IMO, but too much flow may result in loss of power.

CTCOOP

Just did the Fister mufflers (1.75'') with fabspeed x pipe (6 speed Cab). It sounds GREAT (IMO) but I can't imagine wanting it even a little bit louder than it is currently. Although, I don't know that the 12% difference in diameter can truly be equated to a 12% increase in sound - I would think less of an increase. Going to need an engineer to weigh in on that one...

Anyways, sound is always personal preference, but my new setup is LOUD with the top down over 3K RPM. As in people turn to look across 3 lanes of traffic in town wondering what that sound is

Iceter

The math isn't that simple. The area of a circle is Pi x r, so a 2" pipe has 42% more volume than a 1.75" pipe. Or, a 1.75" pipe has 36% less volume than a 2" pipe, if you're a glass half empty kind of guy. Either way, because the hack is a pressure equalizer and not a flow improver, I don't see how it would affect the sound level very much. I can see that it might affect the tone--although to the good or the bad, I don't know.

I don't see how improving exhaust flow would decrease power. Bypassing the mufflers could only improve power. However, I agree that it could get very loud, depending on how much flow it diverted around the muffler.

Ducati_John

The muffler is an acoustic low pass filter - it attenuates high frequencies coming out the engine via the exhaust pipe. When you do the gundo hack, you are partially short circuiting the acoustic lowpass of the muffler. This means more high frequencies get through. When I did my 2" hack, I got about 20dB more output between 150Hz and 600Hz. This changes the tonal characteristic of the exhaust sound. In my case, I heard a lot more crackles on deceleration and in general it sounds raspier. A smaller pipe would be less of a bypass and would tune things a bit differently. Without making a more detailed model, I couldn't say exactly what it would do, but generally I'd expect less increase of high frequencies compared to the 2" pipe. I took some measurements of my 2" hack with Sharkwerks bypass and posted them here:
https://rennlist.com/forums/997-foru...l#post13403188

Blu311

I did a 1.5'' and while it sounded a lot better than stock, I wish it was a bit louder (and I don't really like loud exhausts). So if I could have do-over, I would go with 2''.

Dan@SharkWerks

I had a call about this earlier and wanted to address this topic. We also just installed one today (2009 PDK with no side muffler mods) and there are no vibrations on the car at idle or in Drive at a stop.

I don't know if it's due to what we changed with the design over the years (we now have added clearance for PSE side mufflers and completely changed the bracket system that attaches the muffler to the car), but I have not seen a 997.2 vibrate with our center exhaust for at least 4 years now. I believe that issue is 100% fixed. This was very early on with our first designs which may have not fit as nicely onto the header flange as well.

It was very rare anyway - I heard maybe 3-4 complaints over the years on these from customers and the parts were not installed here so I could not check clearances vs side mufflers, torque etc. to confirm, but we also never heard of this happening on cars with PSE or Gundo / FD hack.