Im getting my 88 RX-7 Straight piped pretty soon, the cat is gutted, car is N/A and completly stock, along with the pipes, ill be getting 2 mufflers thrown on aswell....What I was wondering Is what Size Piping should the 13b go could with? I heard they need a good amount of back pressure to operate decently, and the Shop Im going to kinda needs to know haha.



All help is appreciated, thanks!

 

Back pressure is always bad, always.

The only reason the 2nd gen requires some backpressure is to provide a pressure signal to the aux port actuators, which open the aux ports around 3800 RPM. However, this can be easily converted to use air pump pressure so you can run a proper open exhaust.

I think you will be surprised as to how loud the car becomes. It is almost not worth the trouble for the few HP gained, because unless you go to a header, your gain will most certainly just be noise. The stock exhaust manifold is where about half of the restriction lies so even if you are running a free flowing catback, the engine is stick breathing through a bathtub drain.

Controlling noise on the NA is a real issue. Once you gut or replace the cats, the mufflers have to handle all the noise and that doesn't work very well. I'd suggest instead of running a straight pipe, run at least a resonator in place of the cats. It won't hurt flow but will significantly cut down the noise.

 

Straight pipe it with 2 1/4" piping. The first thing you will notice is how awesome your throttle response got AND they sound awesome with straight pipes.

Do it.

 

You're going to need a presilencer of some sort in between the engine and the mufflers. The one exception to this would be if you have stock mufflers, Racing Beat, or some other brand non-straight-through mufflers in the rear.