Quick question. I have a 1987 GXL and im wanting to cut off the cat and the resonator. only problem is i heard S5 or S4 i think it is something about the aux ports. Im not sure if mine is S4 or 5 im still new to the rotary. Wondrign if it would hurt anyhting because i already have the second cat of and its been converted to single pipe as well.

 

i think u have a s4... the thing your lookn for is a air runner coming off of the 3rd cat "the last one" and runs along your exhaust it comes up into the engine bay with a rubber hose hooked to it ,near your exhaust manifold. if you see it you have a s4

 

Yes, the '87 is an s4. 86-88=s5; 89-91=s5. On the s4 you need exhaust backpressure from the cat to run the aux ports. If you remove the main cat they wont work anymore unless you come up with another way to operate them. This will result in a noticable loos of power up high. You can also wire them open, but that results in a noticable loss of power below 4k.
Also, read the FAQ sticky at the top of the 2nd gen section, it as lots of good info for new owners and people unfamiliar with the car.

 

1986 to 1988 are S4.
1989 to 1991 are S5.

The GXL is naturally aspired with 6 ports. At lower RPMs the first 4 ports take in air, but beyond 4,000 RPMs the extra 5th and 6th ports kick in to suck more air and more fuel for more power. I imagine you want to keep these extra ports alive for high rev driving unless you want to drive like a grandmother.

 

if you really want to ditch the stock cat, there is pre-silencer by racing beat that has the flange, so you can keep your air tube to continue actuating the ports. thats what i would recomend.

 

Yep, the racing beat presilencer is pretty much the only way to get rid of the cat and keep the aux ports working like stock. To get it to work you also need the N/A downpipe, and those together will replace all of the cats. I think they're about 300 bucks, but they reliably operate the aux ports regardless of the rest of the exhaust and are very high quality so they should last the life of the car, unlike other cat replacement pipes :cough: bonez :cough: