Drilling out MILLTEK HFC's...

B6/7 S4/RS4
#1

Gents,
I have drilled out about 4 OEM cats, they are a piece of cake to drill out and remove. I recently obtained some nice Milltek downpipes. Each downpipe has 1 HFC. However these cats are a much much stronger metal and harder to drill out. I Have 2 hours into the project and yet to even have one cat sucessfully hallowed out. I have tried 3/4 paddle bit, 1" paddle bit, 3/4" Metal Black oxide bit & 1" black oxide bit… None are proving succesful. I am getting so frustrated, that I am about to have an exhaust shop just cut and weld straight pipes in place of the cats… However, I have tonight free (preparing for St. Patty’s tomorrow) and want to give it one last go… What methods have some of you used on Aftermarket cats… If you drilled out OEM cats, that doesn’t quit apply as those are a peice of cake.

thanks!

#2

Picked up a 1 1/2" metal hole saw bit… it was working great, until it blew the motor out in my Dewalt drill… FML… this project is going nowhere fast… the inside of the Millteks is an extremely dense metal honeycome that will not break into peices… I am thinking i have to have an exhaust shop cut the cats out and weld in straight pipes…

#3

Cutting out the Milltek is probably the best option. Just make sure they get the angles right when installing a new piece. The Milltek are known for having impossibly difficult material to drill out, which is ironic considering they’re much more prone to failing than the stock cats.

#4

I know haha. They are like $1800 cats that fail after 10,000 miles (that’s how I got these) … Yet impossible to drill out… and yes, the angles are my only worries about an exhaust shop

#5

The RS4 MAIN cats are impossible to drill out, ask me how I know. The pre-cats were a joke just like the S4 ones. 15 - 20 minutes per side tops. For the main cats I had the exhause shop plasma cut an opening for me to remove the main cat, (still wasn’t real easy btw) then weld it shut. I’ll post pics later today.

#6

Has anyone tried an air hammer/chisel

#7

Yes, that’s what I use. 18", cold/drop forged air chisel. Didn’t do squat except get stuck repeatedly in the main cats. I’d highly suggest making an opening and then welding it shut if anyone is dead set on removing RS4 main cats.

http://i834.photobucket.com/albums/zz269/NY07RS4/2007%20Audi%20RS4/OEMCATS.jpg

#8

Yes, I also thought about cutting the cats open/removing inside & welding shut… I borrowed one more friends corded drill and am going to give the metal hole saw bit one more chance tomorrow. The hole saw bit was actually working this weekend until I blew my roommates drill up.