Fake dual exhaust vs. single, what is the general concensus?
 

I am seeing that a few RX7s with aftermarket exhausts just use one large pipe with one muffler, vs. the fake dual exhaust the cars had stock. Is this a typical thing to do w/ these cars? I'm guessing that the Y split in the stock exhaust probably disrupts flow and that a good single exhaust probably flows better?

They weren't 'fake' stock. They were dual exhausts from the Y pipe back. Most of the time people switch to a single exhaust b/c its cheaper, less weight and offers the same performance. That is why the FD went back to a single exhaust.

The stock exhaust was for show and not go. The 'y' pipe hurts flow but allows for 2 muffles which makes the exhaust noise 'nice' for the average daily driver.

I am used to working on American V8 rwd stuff with two pipes all the way from the front to the back. Hence "fake" dual exhaust w/ the Y. I like the way the RX7 dual exits look but if the Y is a flow impediment and I do have to replace the exhaust anyway, I might do a single.

What size tubing should I use for an NA car single exhaust, 2.25"? I am going to build it with mandrel bends.

If you want to make you own I'd look at racing beats for design.

http://www.racingbeat.com/FRmazda2.htm

If it was my time and money...I'd buy the RB header, a flange, and gasket and fabricate the rest from some 321.

Please, the y-pipe being an impediment to flow? It's going to be a tiny one at most, so don't worry about it. Most people go with a single exhaust system when using aftermarket parts because they're too cheap to buy 2 mufflers. Rotaries are loud as hell, so 2 mufflers are a must for any street car.

Na true duals are pretty dope and sound amazing. The turbo guys usually always go single for the weight and what everyone else said...my old duals were quiet though which is why I liked them. That and it just looked right on the car. I'm single now :) Saved a good amount of weight and a few headaches putting the exhaust on.

I have a single 2.25" no cats to magna flow muffler on my NA, and it sounds nice, not too loud at all. However I don't have headers on, with headers my car would be sooooo freakin' loud it would suck.

So if you are going to do a 2.25" single with headers and no cats, you gotta get a resonator in their plus muffler if you have any sort of laws against loud cars.

But yeah the single is lighter and performs better than the dual. The dual looks nicer and its quieter so less attention from cops, but thats about it.

If your going to think like that then I'll take it a step farther and point out that "it's a street driven normally aspirated rx-7 so why add an exhaust at all? You will have a few dollars less, a few hours less, and a 20 year old car that's annoyingly louder and a little less slow."

:D

You have a good point with that comment. The exhaust really doesn't add much 'power' and will add sound. Mine got tiring after a few years.

are you guys crazy? adding exhaust to a rotary ads a shit ton of horsepower! When I did the exhaust on my car it was like a night and day difference in throttle response.

The noise level was a bit annoying though (I didn't mind it, but the police did)

The difference for an NA rotary with a dual or single is less than 5 hp...honestly you won't feel it.

I think the most significant increase in HP I have obtained is by replacing my exhaust starting at the exhaust manifold with 2.25" (non mandrel lol)with no cats to a magna flow muffler. My throttle response increased so dramatically it gave me an erection. I can keep up with KA 240s in the low end now which is awesome for an NA FC, and of course roast em' in the high end.

Just gutting the 2 pre cats gave me such a dramatic increase in power that it stopped me from selling the car like I had originally planned when I first got it. A year later is when I did the rest of the exhaust work.

wow I'm bookmarking this thread. I've always seen the single vs. dual but I never thought about the difference it makes, or why anyone makes the transitions.s

That stock dual catback was used by Mazda to allow them enough flow, while keeping the noise down. A single muffler would either be too loud, or not flow well enough. This is well documented (ie. Yamaguchi books).

OEMs have different concerns then enthusiasts.

The header did help a lot more than the cat back. The cat back alone on my 88 GTU didn't add a lot of power.

Everything helps a little so it depends what your goals are and what your tolerance for sound is. At first, I was quite happy with the full RB exhaust - headers back. It got old after a couple of years.

I defer to Aaron for actual numbers and accurate technicals since I've been out of the FC scene for a long time.

I got the stock duals on a base model and it was pretty quiet until I blew out the manifold to what would be the 1st pre cat gasket... its straight piped... (bought it that way..)

On the flip side.. My friend has an 88 gxl with a 2.5 inch long tube header to 2.5 all the way back to a single his is hella loud!!

So the dual exhausts that come stock on it work fine and if up grading but want to keep the noise down, I should look for another dual exhaust? (ignoring costs)

^^
Racing beat sells a dual that is popular and gives you a little horse power I suppose.

Honestly a single pipe cat-back exhaust system is not loud at all.

Even a straight pipe single exhaust system is not terribly loud. Its when you combine that setup with headers does it get crazy loud.

I can post a vid of my NA if you want me too. I have stock exhaust manifold -> single 2.25" straight pipe -> magnaflow muffler. Heck you are so close to me you can just stop by my smog shop and hear it yourself.

3inch downpipe to nothing but a muffler like I have on my TII? NOW THAT IS LOUD. Got pulled over the first day I drove it to work.

The single/dual argument is pretty much an example of "six one way, half a dozen the other." A dual exhaust, even when it's collected and split as in the stock application, will flow better and reduce noise somewhat. A single exhaust, however, will be cheaper and save weight.

If you're trying to decide which one to go with, it's basically going to come down to those 4 points.

Personally, I have a stock or near-stock header (which will be replaced someday,) a straight pipe/test pipe in place of catalytics, and a Borla catback dual exhaust. I'm quite fond of my own setup; it's good at keeping the noise to a reasonable level while having a nice tone, didn't cost an absurd amount, and I think it looks nice.

If you want further help, you should tell us exactly what you're looking for out of the exhaust. If you want power, frankly, you'll see your best power-per-dollar-and-time ratio from gutting the catalytic or replacing it with a straight pipe. Second biggest gain for the money and time is the header.

Yo gracer7-rx7 correct me if I'm wrong but I know that's the corkscrew in laguna seca in your avatar!!

^^yup :D

That is me at Laguna on Monday of this week! Woot:ylsuper::ylsuper:

Wow your sooo lucky !!! I have had dreams of tracking there!! where is it exacly? And how much do you pay to track there?? Awh man that is awesome!!!

are there any good single exhausts for the FC? Preferably something without a can muffler

I remember on one of my trips to japan I passed by Tsukuba circuit and just hearing all of those cars racing around gave me goose bumps! Man, I cant wait to move to Japan! (bringin my USDM FC with me of course! :lol: )