I think I already know the answer to this, but there's harm in getting some input.

I'm about to buy a 2.5" hi-flow cat for my 87 NA. One shop is very close by and carries Magnaflow. When I mentioned it was a rotary and high exhaust temps, the guy on the phone called the Magnaflow warehouse.

They carry metallic or ceramic hi-flow cats. The warehouse recommended the ceramic. It's a little more expensive, but not by much.

http://www.car-sound.com/02product/u...al/549spun.asp

I like the sound of it and that compact design is a big plus. The exhaust on the car is a single, btw. Passenger side.


Does anyone know whether or not it matters if the hi-flow cat is placed before or after the presilencer (forgetting the air tube for a moment?)

 

The cat is usually placed after the presilencer

 

well cats go before anything. presilencers are mufflers that are free flow. in the Rx7s presilencers usually replace the cat, if you don't need it for emissions