It looks to me that the ypipe that came with my SLP 1 5/8" headers is about 2 1/4" in diameter. I want to put in some cutouts right before each of the cata in the dual cat setup. I see they offer 2 3/8", 2 1/2", and 3" on summit racing. I assume the 2 1/2" ones would work, just slip the y pipe inside and weld, right?

Also I need to get two new cats.The only company I see that makes direct replacement for these is random tech and they are $160 each just for the cats!!. Catco has a complete setup that included the ypipe (which I don't need for like $283. I would be cheaper to buy that setup and just not use the ypipe. The sized on the Catco setup is 2 1/4" in and 2 1/2" out, so it would weld right up to the cutouts as well. I think.

in summary, what size cutouts should I use? and who knows a good freeflowing replacement cat setup ?
thanks

 

as far as I know the SLP y pipe is 3 inches so you should get a 3 inch cutout.

 

Theres no way its 3". I think they say 3" collectors, but the pipes from the collecter down to the cats appear to be 2 1/4", depending on how you measure it, but no more.
Im going to get 2 1/2" cutouts and 2 1/2" in and out cats.

 

Did you buy your headers used? Do they already have the turn on them that mates to the cat?

 

he has the dual cat setup y-pipe which came with 2 1/4 pipes to the cat and then after the cats merges into 3 inch with the other stock "y-pipe" into the i-pipe.

yeah i would try the 2 1/2 cutouts since u cant find anything smaller.

 

They are used/new. A guy bought them from SLP, didnt install them, then I bought them so really they are new. Yeah, they have a kind of flared end, and measuring with a ruler they look like 2 1/4". I saw 2 3/8" cutouts on summit, but Im thinking might as well go with 2 1/2". The smallest diameter in the whole system is the 2 1/4" y pipes, but there are two of course. So after the cats everything is 3" . I need to find some free flowing cats for this system. I dont want to buy the direct fit because they come with y pipes too which I dont need. Im thinking just buy two 9" carsound high flow cats and have a pipe that connects the two fabricated (2 1/2" that goes to the 3" catback. Ive heard that cutouts before the cats can give you 5 to 8 hp more. That would definitely be worth it for racing.

 

Oh, now I understand. You want to put 2 cutouts before the pipes merge into a y. Why dont you just put a single 3 inch cutout after they merge?

 

If I put the cutouts before the cats, Im running without the cats, less restriction etc. I have a Borla adjustable exaust, with the largest hole plate in there, so the 3" catback is just about straight pipes anyway, hardley anything goes through the muffler. I want to bypass the cats. I hear that gives somewhere around 5 to 8 hp.

 

What I mean was put a single 3 inch cutout before the cat. It has been done before. Check out the guy who has a stroked 305. He did a nice job with his.

https://www.thirdgen.org/techbb2/sho...before+the+cat