THis is the one i want to use.....

This is the one i have on there now

Why?



What is the opening on each?

Are you going to weld a flange to the "new" one?

What are the lengths of each?

What are the mounting bolt sizes of each?



Why?

I thought this was off an rx-7 im not sure what year i have all the other cats and needed the big one....so i was hoping this would work as my cash is very straped I have access to torches and welding equipment.

no reason it wont work as long as its in good shape

Well, if the "new" one has too small of an opening, then you will be creating a high restriction point in your exhaust.

If the "new" one is too short, you'll have to weld an extension tube on it.

You should probably weld flanges to the "new" one, with the proper bolt size.

And, put the airpipe flange ion the "new" one in replacement of that press fit end it has.



What is wrong with your old cat? If it's just clogged, then gut it for now and spend some time collecting money for a decent replacement.



Also, I *think* it's illegal in most states to put a used cat on a vehicle, especially if it's not a factory match.

I would think he knows not to put a smaller one on there



its not like a RX7 has a super large diameter exaust to begin with.

It is a smaller cat and im not in the states, i thought this one was from an rx-7 so i thought maybe it was from a turbo or sumthing and would work it is almost the same length except where it has been cut off...

if you have the means to go welding on things to test them

out then knock yourself out and go for it!

Will it screw it up if i use a smaller cat? Im also replacing the front two with two used ones that are in good shape.