Friend offered me dyno time with wideband O2 (same guy that is giving me slicks). Looking at drilling a 7/8" hole about 2" above the upstream O2 on each tube (i have no inner fenders, nice and easy to get to), then have a bung welded to sheet metal that I can hose-clamp on for testing, then slide down to cover the hole once we're done.

Metal shavings will inevitably fall down towards the pre-cats. Would they hurt anything? I may try to stick a borescope magnet down and fish some out, doubt i'd get all of it.

 

If you drop the exhaust flange down and put a rag down inside the pipe and then drill the holes, you should be okay. And then pull the rag out with the metal shavings.

 

but the shavings will still be above the pre-cat?

 

Then the answer would be yes. The metal would get hot and may cause the honeycomb in the cat to fail in time. When you start drilling the hole, use wheel bearing grease and try to remove as much shavings as you can.

 

are you running a stock y-pipe with a pre cat on each side?? i ended up taking mine and sawing in half in the center of the cats,tore the guts out and welded it back together,then used a spark plug non fouler to mount the downstreem 02 sensor,no codes after doing this..and should free up a few extra ponies as well,but,if your town is big on emissions checks,i wouldnt do it..

 

+1 ... Coat the drill bit with heavy bearing grease. I'd also hold a vacuum cleaner hose at the area while drilling.

 

I'll do the grease and vacuum together. Good idea! Thanks.

 

vacuum cleaner will do the trick and if you have a good drill it shouldnt let the filings fall inward anyway. but i dropped a 12 mm bolt in the turbo inlet on my gti and i used my shopvacuum and it pulled it right out. so it should do jusdt fine for little filings. but i was going to ask why not just use the stock o2 wide band or no the ecm should give you a reading anyway

 

factory O2's are narrowband. They either read 1.0, 0.600, or 0.00 volts. And I can't pull a factory pre-cat O2 to run a wideband else that bank (or both banks) would throw codes and who knows what they'd do….

I was going to start with an 1/8" bit then take over with a unibit.

 

Maybe this will help. When guys need to install an exhaust gas temp sensor in the cummins, instead of removing the turbo and the manifold they just start the truck up and drill the hole. The pressure blows all the shavings out.