Diameter of exhaust 1989 4Runner
 

So I ordered a catalytic and muffler. Parts came in last night. The inside diameter of the inlet/out of the catalytic is 2". The ID of the cat-back exhaust is 1 3/4". This is wrong isn't it??? Is the catalytic correct or the exhaust? I have a stock 22RE 1989 4Runner. I'm pretty po'd because this website supposedly only picks stuff that fits your vehicle...

Thanks for help.

Well, 1-3/4" ID tubing will usually slip fit inside 2" ID tubing, since the wall thickness is usually 1/16".

2-1/4 is optimal. 2.5 is too big, not enough back pressure. Any thing under 2 is too small, too restrictive. Stock size is prolly what they picked for you, but it's too small and restricive.

I can't slip fit it because the 2 parts already have the flanges welded on.

I am going to pull the current exhaust apart tonight or this weekend and check the current ID. The OD of the current cat-back is 2" but it looks like it necks out larger at the flange where it connects the catalytic outlet. www.autopartswarehouse.com doesn't display what the ID of the parts are on their site. Go figure :roll:

Just bolt up the flanges then and call it good. My factory cat is 2" ID and the factory exhaust was about 1-5/8" ID as I recall. I think the idea was the cat is a little restrictive so making it a little bigger inside helps to offset the restriction. Plus it is likely a standard sized cat, not like Toyota goes out an designs a cat exactly for each vehicle. They probably pick an existing design from their supplier and go with that.

I re-piped my exhaust with all 2", it seems to work fine. Did not lose any low end torque and it runs strong up to 5000RPM which is about as high as I like to push it.