Anyone running a true duel exaust on there n/a?
 

Well, the week after X-mas, my 90 is going in for a minor exaust change. :) I"m currently running a RB header, into a extremely high flow cat, then into the RB Y pipe, then RB mufflers. What i plan on having done is going from the header directly into two Racing beat pre-silencers, then to the RB mufflers. So it will be a twin 2", true duel system, that never collects. Of course it will be all mandrel bent. So basically it will be the almost the same exaust that my peripheral engine had on it. Hopefully it won't be to loud,:D

Whats everyone else run for there exaust?

By the way, after it goes on, i'll have a race pipe, high flow cat, and the RB y pipe for sale. All you would need to have is a set of mufflers for it, and you would be set.

CJ

i've been thinking about switching over to the duals, but there is no way other than replacing the whole exhaust, that you could pass emissions. at least with the single outlet header you can swap in the cat with a lil spacer just to take the test. How do you plan on handling that issue? I'm kinda stuck in the middle, on one hand there is the added performance and on the other hand there is the added criminal aspect. :)

I have the complete stock exaust sitting in my garage:) CJ

sweet!i'm actually planning on doing the same,i have the header allready...yet to get the presilencers and mufflers.maybe i'll have to come down to portland an listen to yours,as noise is definately a concern.i went to the tech meet down at pineapple last month[?],and spoke to rob about it,he sayd,for a cheap alternitive,i could run some walker super turbo's[i guess that one guy-pohl,i think-is running'em on a pp rx3,so flow should be fine].also,rob told me,to keep noise down,move the mufflers as far upstream as possible,i.e,have the tailpipe as long as u can...a bit hard to do on a 2nd gen,thou.u spoken to him about it?u know him pretty well,dont u?anyhow,definately looking forward to hearing ur results.
david

On the 87 N/A I use 16-MZTX-0010 http://mazdatrix.com/r-ex86nt.htm Please as punch with it. I left the acv and airpump on. The header on mine has a 1/8 inch line off the front header to activate the aux ports. I was'nt too keen on that and rigged up a solenoid that triggers off the 3800rpm signal to the relief solenoid to open the aux ports. Solenoid is connected to the output hose from the airpump and from the solenoid to the little tube that feeds the aux ports. Its not too noisy for me. At hwy speeds its a pleasant tone. The extra power is there. Its not one of those *I think theres more power* things. Its there without a doubt. On the 87turbii I have the 16207 http://mazdatrix.com/r-ex86nt.htm Its a stop gap meassure until I decide how much mullah I want to throw at this thing. Running a smidge below 8psi boost.

Yeah man I got true dual exhaust all the way back, but I did it the cheap gheto way. I got pace setter header, (i know, i know) but for $120 bucks you can't beat that, just becarefull with the studs in the block becasue the flange isn't as fat as it should be. anyways I went JC witney crazy and bought the pace setter catbacks (which also suck) 2 mufflers and a y pipe for $210 then I took my car to a local tex mex muffler shop and got 2 1/2 in pipes welded back to each muffler, I started my car and it sound like when you were a kid and you put basball cards in your spokes on your bike but 10 million times louder so I got them to put an H crossover where the two pipe splits and that muffled it alot, gave me more low end power, and a lower exhaust tone

The only thing I can tell you is if you go true dual either get presilencers or get a really quite muffler, because ever since I have done this mod The coppers really pay alot of attention to me, I get harrased all the time me being a 17 year old driving an import thats louder than most diesels. I get pulled over for everything you name it, no front liesence plate, blinker out, acceleration, speeding, SMOKING, but I realised if you treat them like another car lover or talk to them about smothing off the subject they will let you off, I've been pulled over 4 times on this road near my house for speeding, or peeling out. Sorry for making another topic but I belive if you want your car to sound NICE then buy good quality mufflers or presilencers.
I took the cheap way out and I'm paying for it now

I have a true dual exhaust on my 89 gtus. Instead of using RB presilencers, I used straight tubing to where the Y pipe begins, and then mounted two 28"X 3" long glasspack - type silencers where the Y pipe is normally, (I repacked them with stainless steel wool - its the same suff as in the RB presilencer --i took one apart to find out --you can pick up SS wool at any grocery store both silencers cost me ~$100 instead of $500 from RB) and finished with 2 RB mufflers. I used tubing purchased from M-trix, (thick walled) mandrel bends, and a RB dual header.

I had a Collected header sys before and noticed a solid increase in power with the dual. Top end was MUCH quicker.

The system sounds very nice. With the thick tubing its actually very quiet in the car, but very very loud from the back. Never heard a 7 sound like it -- deep raspy sound.

Make sure u use the thicker tubing + consider the 6 port actuation if equipped. I had it on an 87 before, and I used the RB header with the 6 port pick up off the front rotor. I removed the port for the 89 and kept the smog pump & ACV working for port & vdi actuation.

It was a very nice upgrade (but a lot of work if you frabricate it yourself:)

I may want the test pipe, hi-flo cat and the y pipe when your done with it, how much are you looking to give it up for :D

Yes there is, all you need is two collectors one "after the header" and one "after the cat". Any exhaust shop can custom made them if you provide the flanges.

Yeah, the turbo walkers are cheap, good flowing mufflers that don't burn out. This new exaust will be the same as the pp exaust except for the rear mufflers. Like Pual, Rob, and Chris (You may have seen him at the meeting too.) I too ran the walker mufflers.

I know Rob pretty well. He's a very good friend of mine. Shoot i've know him for about 6-7yrs. Started out cleaning his old shop, doing parts runs, and tearing down engine cores for him back then.

Mark S. I think that a 2" presilencer is only like $120, and the 2 1/2 is like $200. Not to mention, i had them laying around, so i figured i'd put em to good use. :)

When the weather drys up, i plan on doing some 3rd gear 2.5k to 4.5k tests (with a stop watch), 4.5k to 8k, and a 2.5k to 8k timed runs to find out how much bottem end i'm gaining, how much top end, and how much overall. This way, when i put the new exaust on, i can have some kinda comparison. I wish i would have done this from the first day i bought my car. You know, see what by doing a general tune up does for times, then a cone filter, exaust, porting the intake, etc. Maybe you guys who have a stock 89+ can give me some base numbers or something.

The exaust shop that is doing this is actually in the same shop. If any of you guys need some work done, you should give Russ a call. Keep in mind, cars without cats on them are for off road use only. :D I know all of you law abiding citizens would never take smog stuff off of your car.:D

CJ

Make me an offer on the exaust. CJ

I just got my true dual installed, had a custom header built, 2.25 aluminized piping all the way back to my magnaflow mufflers. At first it was just way too loud, not suitable for the road at all, so I got 2 resinators(not straight through) put in. That quieted it down, but still one of the loudest imports on the road. Everyone that hears it says it's one of the nicest and loudest sounding exhausts they've heard, performance wise, I'm not too sure yet since it's winter here. If noise is a big concern, do not get true duals, plain and simple.

i had the dual header going to two dynomax 2 1/2 inlet 4" bullets($29.00 apiece) to two dynomax 2 1/2 inlet 6" welded mufflers ( $ 59.00 apiece ) it was pretty loud above 3500 but not to bad puttin around if joe law is watchin never showed the slightest hint of burning out i even had them glowing red one night racing ( ha ha winning) on the interstate a 00 civic si running on the bottle they outlasted anything else for the price

I can appreciate the pride of fabricating your own system. Congratulations. On the emissions I do what PP13BNOS does. Keep the old system for that one day a year test. You get faster each year at replacing the thing.

i have dual exhaust. its 2.5 in from cat back. i think?...

I dont think an NA would flow enough air to truly warrent true dual exhaust. it might actually hurt your low end tourque enough to slow you down.

its 2.5 in dual exhaust from the y pipe.

I always though if you had a Y pipe than it Wasn't a True Dual?? Am I correct?

For those concerned about torque, hp and being a stock engine, read this from Mazdatrix http://mazdatrix.com/r-ex86nt.htm

hey CJ
do u remeber what size the walker turbo's where that u used?i looked at whats out there..a bunch of different sizes,i wonder if i should get the biggest one that will fit or just get a decent size/price one..also,from your expierience,how is the sound level[using presilencers,of course]?how does it compare to the rb mufflers?thanks:D
david

To be honest i don't know the size....but i think they are called the mini turbo walker....or something like that.

Quality wise, they are just look like your normal run of the mill muffler. But they don't burn out. As far as noise, it was'nt to bad with the pp. I've heard louder imports than my car. I have'nt ran a twin presilencer setup with the RB mufflers before, but i don't expect it to be to loud. Should be even quiter than the walkers. But we'll find out.

When you guys read the mazdatricks site, it says that the RB mufflers are to loud for them. Its my opinion that the RB mufflers are pretty quite. Not to mention, i just can't see spending around $1400 for an exuast system.


Would someone who has a stock 89+ (or any other n/a) Rx-7 do the tests above, so i can get a base line for my car. CJ

The only thing I don't like about all of this is the "cat cutters". Not only is it illegal but is is very bad for the air. I know alot of people on here are kinda young and don't think about his stuff. but You do wnat to breath when you are 50 right. I was running the true duels on my last n/a. but I had the Randon Technologies high flow cats with it. I go the 3" inlet and outlet even though I was using the 2.5" pipe. These cats don't restrict much at all. and they are legal and air friendly. I ma not an environmentalist or anything but we take too many liberties with this kind of thing. I like fast cars too. but I don't run an air hater on the street. only off road for the truck and the traks for the car.
I urge you guys to think about it and do the same.
the fact that it is the middle of December and it was 70 degrees outside in Springfield should tell you that global warming is real.
Dinosaurs were here little over twice as long as we have been here befor mother nature decided to off them. and they didn't polute like we do.
All I am saying is keep your cats so you can breath with your children and grand children

Well this is all very interesting. I have had a semi-true dual exhast on my car since just before SS4 earlier this year and thought I'd throw in my 2 cents.

The entire system is 2" OD pipe. RB Road Racing header kit > custom dual midpipe > CatCo 2612 dual in/out high-flow cat (crap, read on) > seperated Borla y-pipe > Borla mufflers.

My impressions:
This system is way TOO loud. I think I'm somewhat deaf now. :p The power increase at top end was nice, but bottom end is definately weaker. Fittment of the system was a bit rough, but I did all of this myself.

Problems:
The cat died. Literally. The core has completely burned out! I'm not sure if the CatCo cat can withstand a Rotary's hot breath, but coating the cat's exterior with ceramic was a mistake!!! Do not ceramically coat cats. I found out when I was trying to fix a couple of leaks and peered inside the back of the cat. The core was hollow!!!
Also my leaks turned out to be mis-clamped junctions at the back of the cat, and a leaky weld near the RB dual header flange. Welding is definately an art and since this was my first system things were bound to go wrong. At least I can take solice in the fact that only one weld was faulty!

My plans:
Since the CatCo cat was such a failure (at least it was inexpensive) I'm replacing it with two Random Technology 8100 series bullet cats (like a bullet muffler with a 4" OD can and air inlets). Also, to help keep things a bit quieter I'll be adding a couple of Mindtrain presilencers to the y-pipe area. Hopefully in combination with dedicated cats the car will be somewhat quieter and will pass local emissions.

An optional idea:
While discussion various peticularities of exhaust system design with Fred at Mindtrain (very helpful, and very talkative!) the idea of adding an H or X pipe was introduced... it's something that I've been curious about for a long time. According to him (and my reccolection of our dicsussion) it has the following benefits: reduced exhaust noise and (if tuned properly) cross-port scavenging.

The reduced exhaust noise is coceptually very simple. Since you spread the balls of exhaust from each side across each other each individual pulse will travel down both paths and be dampened by each. Thus each pulse will be 50% quieter than before.

Cross-port scavenging is a bit more complicated, and one of the basics behind brideing dual exhaust systems. The idea is: when each exhaust ball is released from the exhaust port it must deal with the transistion into the exhaust system. In stock and most normal systems there is a + positive pressure present in the header (or manifold) for the exhaust ball to fight. Behind each ball is a negative pressure zone (or vacuum). If you bridge the exhaust you're trying to get that negative zone to evacuate the exhaust path before a new exhaust pulse is released. The closer the bridge is to the engine the faster this occours and the sooner the optimal harmonic will be reached. According to Fred, the desired distance (from the exhaust ports) to match the 3000 RPM harmonic is between 35" and 38". Not a simple concept to swallow or enforce indeed.

H pipes and X pipes work similarly. They both bridge the exhaust for the above beneifits. The H pipe's advantage is simplicity. It's pretty easy to cut and weld in. The X pipe offers a slightly better flow pattern and may perform sliglty better overall. NASCAR drivers locally have all switched to X pipes (according to Kip of SK Performance).

Anyway... enough about theory and stuff...

The Random Tech cats are on the way and should be here by the end of the year. Once they arrive I'll be working on my car non-stop getting this system put in.

I haven't decided if I want to keep the system completely dual or crossed over. I like the idea of taking advantage of the naturally occuring harmonic at 3000 RPM, and I want my system to be as quiet as possible (I know it'll be loud), so I may just add a H or X pipe.

Does anyone have any additional knowledge or expirence to throw at this? I may talk with a few more experts before I actually have at it, but if anyone can add anything I'd appreciate it!

To learn more about exhaust configurations goto http://personal.riverusers.com/~yawpower/ and check out the tech. articles. Very informative reading.