Just picked up a dual outlet header (similar to the RB RR header) from a buddy and i would like to know what setup will give the best power gains but also keep a borderline streetable noise level. I know there isn't going to be a big jump in power but i would like to achieve as much as i can. I have done quite a bit of searching and i haven't exactly found anything related to this question. Is there anyone who can guide me through the seemingly endless range of options, and help me pick whats right for me?

 

what other modifications have been done? a better flowing exhaust will net some gains, but the style of exhaust and gains to be expected will vary greatly depending on what other supporting mods have been done, and how well they mesh with eachother.

 

The only other mods that have been done to the engine are AC system and rats nest delete along with a stripped nikki with mechanical secondaries, a more free flowing air filter setup and the honey-comb oil cooler was replaced with the earlier style front mount oil cooler. i was looking into getting a new carb as well, but i hear quite often that reliability goes down the drain when you do so, so i'm probably just going to stick with the stripped nikki for now.

 

I have a similar header and stripped nikki as well. My exhaust is dual all the way back and collected just before the racing beat prima flow muffler. Noise is not too bad and power feels good. I wouldn't be scared to go away from the nikki...a weber or a holley can be just as reliable as long as fuel pressure float level, jets etc are all correct. good luck.

 

I was thinking about a setup sort of like that, where i would run dual 2 inch pipe back from the header, a pre-silencer for each pipe, then collected before the rear axle, and 2.5 inch pipe over the axle to some kind of muffler. That is what i have been reading alot about. But i have not read anything about how well that setup performs and what type, and size mufflers work best for that application. Also does anyone know what gauge pipe works best to keep from sounding to "pingy" if you know what i mean?

 

I would say 14 gauge minimum. But racing beat etc use a much thicker (.125"??) As for mufflers/presilencers, you can use magnaflow readily available (summit jegs etc) or just spend the money once and buy the racing beat stuff. Its heavy, but it lasts a very very long time.

 

are the racing beat universal mufflers any good? im trying to keep this to as inexpensive as i can.

 

just as good as their made to fit stuff. These mufflers and presilencers are ideal if you have a non rx rotary powered car that needs quieting down. Same packing material inside mufflers as the power pulse. There really isn't a "cheap way" out of this with the car not sounding "pingy" save up and spend the money here or end up doing it twice. Go on you tube as well and put in any search combo you want for rx7 exhaust and listen to them and make a decision based on real info, not just other opinions. This will help.

 

also...avoid the Pace Setter products...they are tempting due to low price, but will not hold up to the extreme heat, occassional backfires (lol) and general abuse that a rotary engine will put an exhaust through.

 

Rb runs 11 gauge/.120 wall if you look around their price is actually pretty good.

if you want quiet, buy the "street port"/ 81-82 RB muffler, and just run the two pipes to that.

 

I just finished up replacing the complete exhaust system on my 79 with a mostly custom system and an old (real old) RB header. This header is identical in shape to the pre RX-7 RB 12A header pictures I have seen, and from what i have read and been told, is a real early example of a RB header. I am saying this because my header is actually 14 gauge pipe, compared to the 11 gauge RB uses today. It has a very slight pingy sound to it, nothing too horrible though. I am quite impressed with the power gain though. I built this exhaust using Magnaflow mufflers, 2 of them, with a generic stainless steel body muffler at the back. This is a total of 3 mufflers in the system, with some 2" pipe between everything.

Like I said, the power gains are definitely noticeable, and the sound level is similar to that of the RB system. The exhaust tone is very low, not high pitched or raspy at all from what I have heard so far. Needless to say, I love it and would highly recommend this setup to anyone outside of the USA since getting RB parts shipped so far is extremely expensive. Its hard to justify spending $1000 or more for a completely new RB system when for about $500 I can build my own exhaust system that is just as reliable.

Behind the header, I used 14 gauge aluminized pipe. I bought my prebent mandrel bends from Columbia River Mandrel Bending, fairly cheap and just about the only place I was able to find 14 gauge aluminized steel mandrel bends. Here is the website http://www.mandrel-bends.com/catalog/ . They offer thicker pipe too if you go up to stainless steel and in pretty tight radii if needed.

 

Broken down into it's most simple form, building a quiet, free-flowing exhaust boils down to two things: large mufflers, and lots of them.

Any variation from that theme is going to increase noise, or decrease flow (or in rare cases, both). The Racing Beat muffler, for example, is of "turbo-style" construction (at least the ones I've seen cut open). This hinders flow (though potentially at a level we amateurs might not appreciate).

Any brand of straight-through muffler with construction suitable for the rotary (stainless steel packing) will probably work. For an FB, creating something similar to what Racing Beat uses will work nicely enough: the largest narrow round mufflers you can fit in parallel, merge pipe just before the rear axle, largest offset oval/round muffler you can fit in the rear. Alternately, and I'm not sure about the physics working out for me here so I've never tried it, you could use a 2-to-1 muffler as a merge pipe.

Using thick steel is a good idea too.

 

A 2-1 muffler such as one from Magnaflow or Borla will work decently as a collector, though it is far from ideal. From what I have been reading, the angle at which the pipes converge will actually have an effect on the flow. If you aren't looking for all out power though, don't worry too much about this.

Things to remember about muffler choices on a rotary. Avoid baffled mufflers if at all possible. They tend to sound very tinny and high pitched. Straight through mufflers with stainless steel packing are the best to get since they are more efficient at removing the high frequency tones from the exhaust note and generally flow better than baffled mufflers too. If you have the cash, go for the RB muffler though. It doesn't flow as well as a straight through muffler, being of chambered design, but is by far the best at keeping the rotary engine quiet.