I have a 13b engine in my FC, its the stock engine that comes in a 88 GXL. I was looking into changing my exhaust, i know right now it has a y pipe. id like to add on a x pipe or h pipe, so that i had true dual exhaust. Is the 13b too small for this kind of exhaust? or will it be better and give my car more hp/torque? also i plan on swapping in a 20b engine in the future and i want to use the same exhaust. Lastly, would i be able to change it to a x pipe/h pipe on my own, with the help of a buddy? Or would i have to take it to a shop, i am okay with putting in hours on the car.

 

In the future ONE submission of a question is plenty.

Even if you altered that exhaust your modification would be Useless for the power of the 20b down the line.
You need to look at the diameter of what you want to use NOW rather than later in order to make your idea work.
Yes,sure,look at the Road race header and exhaust on Racingbeat.com..BUT if you go that route you are just going to alter the exhaust again later.
My suggestion is a REVII exhaust or a 3-4 inch single setup.Right now you would be good with 3 inch as it is a N/A and anything more is a waste and will not achieve any additional power to your car anyways.It will just make it plain Noisy.

By the way I hope you are Rich as a 20b setup is not Cheap and they are getting rare.Expect at least 6-8 k for a decent setup,minimum.That is just a half decent engine.

 

An x or h pipe will do no good on a 2-rotor. The collector on the header does all the scavenging. Once that's done, a single tail pipe is the best you can do. Dual outlets are just for show. The highest HP rotaries that require a full exhaust are found in roadracing. They all have a header and then a single tailpipe all the way back.

 

Yea I am running racing beat header test pipe and 3 inch m2 performance stainless single out on my full bridge gxl and I love everything about it sounds good backfires looks good and gave me a large amount of response from when I has my borla set up and the exhaust I have now is 200 bucks a d the borla was 1000 bucks so honestly the single is the way to go on a fc

 

Dual outlets are for noise reduction. Race cars use single mufflers because of the weight advantage, and the louder noise isn't a problem.

As stated earlier, an h-pipe or x-pipe doesn't do anything for a rotary engine. You would be wasting your time, and possibly hurting the performance.

If you have access to a welder, band saw, and somebody to help you with skills, then you can make your own exhaust system. The best overall material is 321 stainless steel, although 304 stainless steel and mild steel will also work. See the below link for dimensions. Don't forget to add a pick-up tube for your aux ports.
Rotary Tech Tips: Exhaust System Configurations

Fair warning, most 20B conversions on this forum cost between $10K and $35K, and we have had some in the $50K+ range. They tend to sell for a small fraction of the cost to build them. You would be better off just buying one that was already converted. As far as I know, this professionally-built car is still for sale:
https://www.rx7club.com/2nd-generati...rtible-767071/

Hopefully it would be apparent that an exhaust system optimized for 150hp would not be the same as one for 300hp, but here are pictures to show why a 13B exhaust would not work on a 20B engine:

13B (2 engine outlets, smaller collector)


20B (3 engine outlets, bigger collector)