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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.
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.
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.
He just told me not to _ever_ ask for a dual 4” system...
This dual 3.5” inch system required raw materials and components are now all catalogued and there are fixtures and prints for everything. It’ll be just a production effort and no longer a development effort for him to make more of those.
The old dual 3” system on my car was almost the same, no x-pipe though.
My (theoretical) research suggests that you’re already knocking out a decibel or two with the x-pipe.
If you furthermore reconnect the flow paths after the unequal path lengths, you’ll 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 that’s not enough, one can always add a electric valve to one of the rear legs and create an active side branch resonator.
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.
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.
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.
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.
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 didn’t have in that system). With the valve open, it’s a dual exhaust. With the valve closed, it’s a single exhaust with a drone-eliminating quarter wave resonator. If my dual 3.5” system will ever feel too loud under cries, I’ll just add that one electronically controlled valve.
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.
02-05-2018, 12:00 AM
