I have a 3" high flow cat that I want to use to swap out my stock 117k mile cat. It doesn't have bolts; it doesn't necessarily look like the stock bolts will work with high flow. What can I use?

 

Go to the hardware store and get some stainless steel Nuts and Bolts so it won't rust.

 

Also make sure you coat them with anti-seize before bolting them down.

 

9/16" head bolts is good

 

I like the JIS flange bolts - http://www.nutsandbolts.com/bolts-me...-c-31_161.html

 

I think I used 1/2" dia bolts with my Mil.Spec cat (3/4" head), but I have an aftermarket downpipe and catback. so if you still have the stock catback and/or downpipe, measure the holes on the flange of the cat, and measure the holes on the the flange of the catback and downpipe where they mount to the cat, then go by the smallest hole size if they aren't all the same. I would also use a flat washer and lock nut (or you could use a split lock washer and a regular nut) at each bolt. Just make sure the bolts are long enough that they thread completely through the nuts once everything is assembled.

and +1 about using antiseize

 

I used M12X40 mm lg SHCS for my perrin cat with tanabe downpipe and tanabe catback. Bought them in stainless with nuts from McMaster.com

The flange on the stock downpipe is a little thicker than on the tanabe, maybe +3 mm, so I would measure before you buy 40mm lg

 

Good luck getting those stock bolts off

 

I was hoping to be able to remove the stock cat without taking apart a lot of other things; drop it more or less straight down. With the bolts on the back of the cat, it doesn't look like that will be possible either.

Is there enough flex that I can get the stock cat out without a lot of hassle?

 

you might have enough flex with the exhaust hangers to get the cat off without pulling anything else off, but I replaced everything at once, so I can't say for sure.

like JJsEvo8 said, it will be a pain to get those nuts off the cat. I recommend spraying them a few times with pb rust blaster or some sort of penetrating oil and use an impact gun. if that doesnt work (and it probably wont), you will have to heat the nuts with a torch until they are glowing.