ok ive ordered a set of 17/8 headers from texas speed for my 02 z28. the car currently has a borla adjustable cat back that i would like to keep. my question is what diameter is the matching ory? can i cut the reduced diameter off and slip a cut out between it and the cat back? what diameter do i need to make a clean slip fit over the y pipe exit and the cat back inlet? i see 3" and 3.5" but im not sure which would be better. should i go with the 3" and stretch it to fit or would the 3.5" be close enough? thanks for any help

 

You could expand 3" slightly to fit or alittle extra welding for 3.5". I'd go 3.5" to be safe. Both ypipe outlet and catback inlet should be 3".

 

This is what I did to my TSP Y when I had it. The outlet is designed for the stock 2.75" I-Pipe.

DO NOT try to expand it!! Stainless splits, not expands. And it sounds funny when it happens

This is what you will need.

Google Columbia River Mandrel Bends.

Hell, here's the link to the exact one I got.

Transitions & Forms / Transition Cones / Page 2 / 3.5" - 3" transition cone.

http://www.mandrel-bends.com/catalog...-cone-715.html

Just be sure to select "stainless" for material. It only adds $1.50



There's a few pics in my old thread here:

https://ls1tech.com/forums/generatio...tall-pics.html

 

I agree on both pieces being 3" i just want to make sure i have a nice linear flow without it jumping to different sizes all the way to the tips. I guess i just need to go 3" and have it expanded to fit over the pipes. Im looking to clamp it in place and the hell with having big sloppy booger welds lol

 

Dr whigham that looks great but i dont know anyone who tig welds and i was wondering if i might get lucky and just clamp the 3.5" onto the 3

 

Probably not and get it to seal.

If your collectors are 3" O.D. you need 3" I.D. for a proper fit and seal. If its 3" O.D. you need 3" O.D. but swelled on one end.

Personally I prefer to put ball and socket flanges on. It make life a lot easier if you ever need to take it apart. I always ended up screwing something up trying to take apart slip fits that had been clamped.

 

Yeah i was planning on using band style clamps to avoid crimping the pipes

 

Stainless splits when expanded? Well that sucks. I had plans similar to the OP with lopping off the end of my Kooks Y (right before it reduces), taking a 2' section of 16 gauge 304 stainless that is 3" OD and having an exhaust shop expand the end out to 3" ID. then have a stainless cutout placed in the usual spot of the I pipe via stainless V-band clamps. The shop deals with 409 stainless so I wonder if it reacts differently when expanded by not splitting?

 

Your best bet is to take cut off wheel to it first. Cut "up" on one leg of the pipe the length you want expanded. Then get that welded over to close the seam. You're pretty stuck with what you have when it comes to stainless.

 

ok after reasearching a bit more it looks like i can get a 3" id cutout from magnaflow thats roughly a foot long or so. I just wanna cut the 2 3/4 piece off of the y and slip the cut out on clamp it in place and trim the I pipe of the catback to fit. anyone see any issues with my plan?

 

Understood DR W. It makes you wonder how do the manufacturers like Kooks enable their slip fit connections to work.

 

Nom, I am not sure a foot is enough as the best place for the cutout is under the rear pasanger seat. I have a cutout welded in right now and did a measurement before I ordered the new section of stainless pipe and came up with 15" or 18" (can't remember which) where the beginning of the I pipe was and where the cutout began. This led me to order a 2' section off eBay.