Does anyone have any knowledge of a Tri-Mil muffler for a 914-6/911 application? My recent 914-6 project has one, but I've never heard of one on a 6 cyl. Mostly just on VW applications.

a pic is worth a thousand words...

This thing sorta looks a “Bursch” style. 2 in and 1 out exiting on the drivers side.

Click to view attachment

Originally founded (1960's) by Joe Miller, Tri-Mil Co. in Compton, Calif. Known for T-1 VW muffler mfg.
Moved to Gardena, Calif., company sold off (after Joe's passing) and is now in the ownership of another VW aftermarket Co.
Your system is designed just like a Bursch, as the orig owner was big on knocking off Bursch...therefore the similarity. Only problem on your 9146 is the Tri-Mil uses too small of a muffler ; they just stuck the T-1 VW (restrictive) muffler on the 911 system and called it a day.
Try to source a turbo-style muffler with an i.d. of (min) 2.250", and swap it onto that extractor...and you will be OK !

.....and Marty comes through with the rest....of the story.
If it's anything exhaust with a 914, especially an older style, he knows the whole back story.

Now with sixnotfour's post...$500 for a bursch, really?!
Maybe I should sell the old /6 version I have in my parts loft for 1/3 the new price

Best solution; if the remainder of the Tri-mil is in decent shape, muffler shop can attach a Thrush or MagnaFlow 2 1/4" id. Have them fab you a "Removable" slip joint/ clamp, so you can slip a straight pipe on for track use. Have the rebooted system ceramic coated for extra HD lifespan= that's where I would spend my $500.
PS, Joe was a man of many hobbies

I was thinking the same thing since the exhaust is in really good condition. Certainly can’t hurt to modify it.

$500 for a Bursch?

I checked the Bursch website and was surprised at the current prices. I remember when my 914 system cost about $150 (yes, long time ago), now they are around $500. Wow!

http://www.burschexhaust.com/914/