I have an 88 formula 305/tbi/auto. Here's what i want: new catco cat, 3in intermediate to dual 3in or flat tips, 4th gen style.
I've searched and can't find this info

I have been looking at the flowmaster single output 40series kit,
In summit it shows the flowmaster exhaust for tbi/lg4 as 2.5in and the tpi as 3in. I'm lost here, If i change my cat to the tpi unit, could i put on and use the 3in cat-back version?

 

I had the same predicament when planning out my catback. I have the LG4 engine on my 86 iroc and i wanted 3in all around. so yea upgrade ur cat to 3in and you can go ahead and get the 3in piping. as for the headers portion just get an adapter for now so the cat can hook up to the headers unless ur gonna go ahead and get the headers alltogether. so my final setup is gonna be: Magnaflow highflow cat converter, american thunder 3in exhaust, and sum flowmaster 3in tips. just waitin on the $$$ and this setup will be mine. hope this helped!

 

thanks, that was what i neede to know. I think for now, i'm just going to do new cat and cat-back. I haven't decided on what brand/style headers yet.