Ok, well i have a n/a fc, and i wanted to do an exhaust setup, as i have heard that some of the best power gains can come from an exhaust/header setup. WIth that being said, Apex'i makes one that is 3 inch. Now is that TOO big for a n/a setup, or woul di be ok running that on my car. is there any pro's, con's to running an exhaust without any other mods with a rotary? thanks!

 

You still require a little bit of back pressure on the NA, but I wouldn't imagine your car would explode with a 3" exhaust, but I don't think the engine will get enough back pressure to open up the 5th/6th ports. I think 2 1/2 is what you're wanting to go for.

But then again, I'd wait for someone else to chime in, as mine is just "what I think", which doesn't count for much sometimes

 

is your car a s4 or s5? As the s4 will need some more back pressure to open the aux ports.

 

understandable thanks! i just know that i have heard a wierd story on how someone put a 3 inch exhaust on a TOTALY stock n/a, and somehoe he blew an apex seal or something? but thanks for the input, all else from knowlegable rotary gods on here is appreciated!

 

mine is an 88 (s4)

 

If I were you I would just get a good cat back and downpipe made for a s4 n/a, and keep a cat on there to keep some back pressure.

 

I would go with a header, high flow cat or pre-silencer, and a 2.5" exhaust.

 

ok so it looks like 2.5 is the preferred sizing? ok thats helpful....now, what about eliminating any of the pre-cats, or anything?

 

go with a header or downpipe to remove the precats, I would choose to go with the downpipe

 

ok, as im not knowing a whole lot about the exhaust side of a rotary yet(previous owner of 9 hondas) are the stock exhaust manifold and the pre-cats one big piece, is that what ur saying, so getting a header, or a down pipe would eliminate them both? sorry for the dumb question.

 

if you are worried about the 6pi system actuation, you could always mod it with the air pump or an electric pump. its easy and cheap+ there are several write-ups on both methods. still tho, i agree with everyone else, 2.5 is the sweet spot on an n/a. like george84 said, either a header/midpipe combo or a dp/midpipe combo will be your friend. it all depends on your other mods and how much exhaust noise you can take. for a stock/slightly modded fc the rb dp/presilencer is a god choice: http://www.racingbeat.com/resultset....rtNumber=16206
for a wilder setup or a track car where noise isnt an issure the header with thye same "presilincer" is preferred: http://www.racingbeat.com/resultset....rtNumber=16130

 

the manifold is separate. you can get either the "cat replacement/ presilcer"combo i just posted, or the header with the same presilencer and both setups will bolt right up to the stock y-pipe or an aftermarket bolt-on cat-back

 

here is a pic of the stock exhaust setup

 

OR make cutom parts since RB is pretty much the singular reputable rotary exhaust maker (although there are others)

 

From the factory there is an exhaust manifold (like a cast iron bath tub), 2 pre cats, and a main cat. I'm sure they were at one point separate pieces, but usually the years of driving fuse them (or the bolts) together with rust.

I came to the conclusion, after asking lots of questions and doing a lot of searching, that no bigger than 2.5", with a header, and presilencer or 1 cat, and a muffler, is best (just as someone had already suggested). I liked my setup for the few years that I had it.

 

ok cool....and noise isnt really an issue...and motor wise it is completely stock...anyone care to post up some setups, so i could get an idea of what people are running on near to stock motors?

 

I have a s5 vert and don't need as much back pressure as you but, I run the stock exhaust manifold, Racing Beat downpipe made for verts (extra cross brace on verts), custom test pipe, Apex'i N1 duels. This setup is pretty loud but sounds really good.

 

True

Yes, it is too big. The optimal size for for an NA 13B is about 1.75" inside diameter, which is roughly 2" outside diameter. From the header outlet, you can gradually increase the diameter of the exhaust if you like.

The fuel injected 84-92 RX-7's have an airflow meter that pretty much compensates for modifications. The later RX-7's, as well as most RX-7's modified with an aftermarket engine management system, have a speed-density fuel metering system that can't compensate for modifications, which is why you have probably heard horror stories about exhaust mods blowing up RX-7's.

There was recently a thread on a similar subject:
https://www.rx7club.com/showthread.php

 

I am using:
stock header
straight pipe with a resonator
Borla catback exhaust (I believe 2.5")

My secondaries work fine.

 

If you want/have to pass emissions you might try the Rotary Performance Header cat combo. it's a Racing beat header and Bonez catthat bolts right in place of the stock manifold and cats. Then just add the catback of your choice. I like the Racing Beat catback myself even though I currently have an old HKS sport system. Not sure if the HKS is sold anymore. Mazdatrix no longer carries it.

http://www.rx7.com/store/rx7/fcexhaust.html

 

Backpressure is bad, this was just talked about a week ago, your goal is to keep exhaust velocity as high as possible. No backpressure, period.

 

What is the stock diamater? Say i just want to get an downpipe to replace the precats and keep the stock cat so the 5th and 6th port still works?

 

Stock cat is probably pretty clogged at this point, might as well get a header and any standard 2.5" cat with an air injection port on it and hook it up to the existing line. Youll have to have an exhaust shop put the flanges on and make the pipe to the stock catback, honestly at that point you're far better off than stock. Stock manifold flows like crap and the cats are a large restriction.

 

Back pressure on a s4 n/a is necessary if you want the aux. ports to open, unless you have them hooked up to work off of something else.

 

No, the velocity of the exhaust gas opens them up.