Im getting a new exhaust for my 90 na. I already have a racing beat header which is stock size in diameter. Im getting the corksport power series exhaust 80mm. And also doing a cat delete. My question is, will i have to get a new 80mm header to fit the 80mm exhaust? Or can i keep the header i have, with minimal power loss, and get a mid pipe that transfers 2.5" to the 80mm?



80mm is 3.1" for those of you who dont feel like doing the math.

 

You'll be fine. Unless you have some serious port work done, there's not much need for going over 2.25".

 

it will be ear bleeding loud!

 

I run 3" piping on my NA with magnaflo hi flo resonators

 

Yes, you can keep the header and use a mid pipe for transition, plus the CorkSport catback is also available with a 2.5" OD flange. However, 80mm is a little big for a NA so you will lose some low-end hp and torque from that. Just a word of warning, with no cat, no pre-silencers, and only one muffler there is going to be a lot of noise.

Just so you know, header pipes and primaries need to be about 1.75" ID in order to work well, and even peripheral ported engines only use 2" ID. After the primaries, the optimal pipe is usually about 2.5" OD collected or 2" OD uncollected. The only time you will see 3" piping for a street-driven NA RX-7 is when a manufacturer wants to stock just one universal piece that "fits" both turbo and NA cars.