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Twin Turbo 928 fixed and back out there terrorizing the streets!

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Twin Turbo 928 fixed and back out there terrorizing the streets!

Old 02-05-2018, 12:00 AM
  #1831  
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I haven't kept up with the whole thread. Who makes it and what does it run cost wise?
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Old 02-05-2018, 10:28 AM
  #1832  
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Originally Posted by 928sg View Post
I haven't kept up with the whole thread. Who makes it and what does it run cost wise?
The muffler is made by John Kuhn, like all the other custom parts of the turbo system.

It's a prototype at this point. It needs to be listened to first before it's even worth making the cost estimates. The hope is that with the infinity pipe and the dual Borla XR-1 cans it'll sound good. We know it won't be restrictive!

It won't be a budget item because the raw materials alone run a fairly high bill. That's because it's meant to last the life of the turbo system and car, whichever is longer.
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Old 02-09-2018, 06:44 AM
  #1833  
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The rear cap of the muffler is now black. After test fitting, this paint job blended the new exhaust into the stock bumper cover the best. The rest of the exhaust will remain bare stainless.



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Old 02-10-2018, 06:23 PM
  #1834  
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Default Exhaust being hooked up

John is finally done with documenting everything and is now hooking up the exhaust. Markings will burn off during the first hour of operation and take their secrets to their graves.



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Old 02-11-2018, 04:17 PM
  #1835  
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Default All hooked up now

The exhaust has been installed:








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Old 02-11-2018, 04:31 PM
  #1836  
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Beautiful work, John!
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Old 02-11-2018, 05:06 PM
  #1837  
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Originally Posted by Rob Edwards View Post
Beautiful work, John!
He just told me not to _ever_ ask for a dual 4Ē system...

This dual 3.5Ē inch system required raw materials and components are now all catalogued and there are fixtures and prints for everything. Itíll be just a production effort and no longer a development effort for him to make more of those.

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Old 02-11-2018, 05:22 PM
  #1838  
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Looks very similar to mine:

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Old 02-11-2018, 09:17 PM
  #1839  
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Originally Posted by 928sg View Post
Looks very similar to mine:

The old dual 3Ē system on my car was almost the same, no x-pipe though.

My (theoretical) research suggests that youíre already knocking out a decibel or two with the x-pipe.

If you furthermore reconnect the flow paths after the unequal path lengths, youíll get some more cancellation. I think Porken did that to a RMB and liked the sound improvement.

Doing the largest possible rear muffler after recombining the flow paths should (by my theory) really smooth it out.

If thatís not enough, one can always add a electric valve to one of the rear legs and create an active side branch resonator.
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Old 02-11-2018, 11:09 PM
  #1840  
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my plan is to move the x further back towards the split, and I know the longer side after the mufflers will have to be redone due to the larger Z06 trans. I was looking at these this afternoon.

http://www.xforce.com.au/xforce-prod...1-300/cid-/vid-

They have a dual 3 in and dual 3 out that necks down to dual 2.5 internally but I think the exhaust gases have cooled down enough to slow the velocity
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Old 02-12-2018, 06:04 PM
  #1841  
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Originally Posted by 928sg View Post
Looks very similar to mine:


You
My custom 3"
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Old 02-13-2018, 05:46 PM
  #1842  
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It's not surprising that many people are ending up with similar exhaust solutions given that we all have to work with the 928 undercarriage and space allowed there.

If someone is interested in making their own muffler, here are some useful links:
http://www.coneeng.com/images/techAs...mbly-Ideas.pdf
http://web.engr.uky.edu/~dherrin/ME510_Old/
https://www.acoustics.asn.au/confere.../papers/34.pdf
http://www.enoisecontrol.com/wp-cont...rrier_wall.pdf
https://crgis.ndc.nasa.gov/crgis/ima...f_Mufflers.pdf
http://www.bmwblog.com/2014/04/30/bm...xhaust-system/
http://ansol.us/Products/Coustyx/Val...escription.pdf
http://data.mecheng.adelaide.edu.au/...ranch_geom.pdf
http://ijiset.com/vol2/v2s7/IJISET_V2_I6_64.pdf
http://file.scirp.org/pdf/JFCMV_2016071214300784.pdf
http://www.m-hikari.com/astp/astp201...TP5-8-2012.pdf
https://www.motor.com/newsletters/20...ngExhaust.html

Short answer for people considering making their own mufflers but don't want to read all those links: Don't! ;-)

More seriously, studying muffler design and then watching John design and make one was a great amount of fun. However, if you are budget and/or time constrained, it's much better to find a well-matching muffler that someone already makes. Unless you have an oddball design requirement like our dual 3.5" in and single 4.5" out in a very specific space envelope, you can likely find a muffler that fits.

In my opinion, for performance car aftermarket exhaust, you want the largest possible case volume, perforated pipe straight thru design and durable packing in the muffler. You don't want chambered mufflers (unless it's a Helmholtz chamber with straight thru flow path) or mufflers that force two 180-degree turns inside the chamber. Using many and large mufflers allows one to use less restrictive models for the same sound level.

For normally aspirated car looking for maximum power, you probably want the first cross-over before the first set of mufflers or the cats. However, my system has a shock-wave trap on both side before the first cross-over, and I think it should work well. For muffler durability, you don't want to combine the pulses the first time inside a packed muffler in a way that pulses equalize thru packing. Using unequal length pipe segments is good, using as many mufflers as you can fit is good, and using as large mufflers as you can fit in each location is good. Recombining flow paths after unequal path lengths will also help a little bit.
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Old 02-13-2018, 07:33 PM
  #1843  
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I checked with XForce today they make the Varex mufflers. The dual 3 does not neck down internally nor does it merge the 2 so it is looking pretty interesting. Size is a concern as the case is 16 long 10 wide and 6 tall. The movement on the top is 3 inches tall which is where I may run into trouble.
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Old 02-13-2018, 07:56 PM
  #1844  
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Originally Posted by 928sg View Post
I checked with XForce today they make the Varex mufflers. The dual 3 does not neck down internally nor does it merge the 2 so it is looking pretty interesting. Size is a concern as the case is 16 long 10 wide and 6 tall. The movement on the top is 3 inches tall which is where I may run into trouble.
If you want to do an active, valved system, then replicating what Greg aka Slate Blue did is, in my opinion, the best option. Install a cutout valve in one of the rear legs after the crossover and the axle mufflers but before the rear muffler (which he didnít have in that system). With the valve open, itís a dual exhaust. With the valve closed, itís a single exhaust with a drone-eliminating quarter wave resonator. If my dual 3.5Ē system will ever feel too loud under cries, Iíll just add that one electronically controlled valve.

https://rennlist.com/forums/928-foru...-3-system.html

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Old 02-14-2018, 10:13 AM
  #1845  
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Installed exhaust video:


No sound check yet. The big-a$$ oil cooler needs the brackets laser cut first, and the oil cooling circuit needs to be hooked up. Then it can break wind from the exhaust, and we'll get some action from the back section as The Beastie Boys used to rap.

Last edited by ptuomov; 02-14-2018 at 06:45 PM.
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