I have read more single vs dual posts using the search than I can read in a lifetime.

However, of all the posts I saw, I never once read anything about the use of x-pipes, or even h-pipes, on true dual exhaust setups.

Is this because the rotary engine doesn't need them? Equalizing pipes are sure to help any true dual exhaust setups -- ask any V8. I was wondering if there was actually any gain from it since I havn't seen anything about it in the sea of exhaust posts.

Thanks.

 

I feel your pain.

There is at least one post floating around on this subject, but I don't remember it leading to much. The thing is, piston engine type balance pipes really don't work well on a rotary. The rotary engine works best with what I guess most resembles extended tuned headers, known as the "short primary collected" and "long primary collected" pipes. Much like tuned headers, the optimum collection point depends on the engine porting and rpm range. The "true dual" term is just slang for an "uncollected" exhaust.

For more information on the short and long primary exhausts, see the Racing Beat 1Gen RX-7 exhaust systems. Mazdatrix is the only vendor I know of that claims an advantage in uncollected exhausts. Since all rotary race cars that I have seen use a collected exhaust, I'm assuming that the Mazdatrix uncollected exhaust's value is limited to street use.
http://www.racingbeat.com/
http://www.mazdatrix.com/

 

Ahh, ok. Thanks for clarifying that up. From all what I've read, I think I want to collect it far back towards the end if the car into a 3" single. Supposedly this gives me a nice torque curve, ideal for what I want to do with it (autocross/track car).

 

You've got it figured out pretty good. Collect it as far back as you can into a 3" single. Then go through a straight through muffler. This works best especially on ported engines. the X or H pipes don't work to any sort of an advantage on rotaries for the exact reasons you listed.

 

What diameter would the pipes be between the engine and the 3" single pipe? 2.25"?

 

The primaries should be about 1.75" inside diameter on a stock or street-ported engine.

I know of one race team which gets good results with a 27" short primary, and then gradually increases the pipe diameter after that. For example, 1.75" ID primaries collecting to a 2" mid-pipe or pre-silencer, and then to a 2.5" muffler inlet with a 3" outlet. Those numbers and components are just examples, but that's the main idea.

 

Interesting setups you guys are talking about...any pics of some of the street or race setups (or even your own...I've been wanting to see a setup from rotarygod for a while now )?

 

true dual are good for low end. and the closer your headers meet together is the more high end you'll have. or so I've read.

 

I don't have anything from the rotary gods, but they tend to live in peripheral port world, so I'm not sure how well their setups would work on the street. However, you can see lots of exhaust pics at the Racing Beat and Mazdatrix sites that I posted earlier in the thread. I use the Racing Beat long primary exhaust system on my 1Gen.

You can see my 20B exhaust by clicking on my www icon (only the 20B car links work on that site, which is owned by my primary builder). The turbo manifold isn't so great because the runners are not equal length, and the wastegate pipe is at too much of an angle. However, the rest of the exhaust was done professionally. The tubing after the Y was kept large for tone, and the dual exhaust is intended more for noise supression than performance. The wastegate bellows helps keep the exhaust from cracking when the main pipe and wastegate pipe heat unevenly while on/off boost. The quick-change cat was my own crazy concept, but the smart guys figured that the v-band clamps were better than bolts, and I must agree.

I can't seem to make any rhyme or reason out of the tuning lengths. When the long primary was shortened on my 1Gen, it gained horsepower but lost torque. I think it depends on the engine, mufflers, pre-silencers, and a lot of other variables.

 

well, torque=low end, hp=high end in a kind of blunt way. maybe that was the case. lol

 

When I said rotarygod...I meant the MEMBER rotarygod ...but if you have someone else that you know of feel free to let me in on it when you get some more info/links. Thanks for the pics though! Did you think up the exhaust sizes and design yourself or did you have help? How long did it take to fabricate everything (difficulty to you...and how about those cans out back...very nice but how hard to put on)? I'm still not really sold on N1's, they're very nice sounding and all of that but I'm just not a big can type of guy . They look very nice on your car though. Was that foot clean ?

 

Hehehe, yes, but I'm still trying to figure out how that relates to the exhaust lengths on a rotary. I have lots of info for V-8's, though. Anyway, some day I hope to have my own welder, bending tools, cutoff wheel, dyno, and lots of time to spend researching this subject. I'll let you guys know the results, which should be somewhere around 2030.

Oh geez, you are in trouble if you think any regular members are rotary gods.

OK, here's how my 20B design went:
1) I tell SPiN Racing that I want a quiet, good-sounding exhaust with a quick-change cat. Well, it was maybe a bit more involved than that, but since I have known Scott for years, and he also has an aviation degree, he knows my tastes well enough that a lot of things go unsaid.
2) SPiN Racing decides on 3" Y with Apexi N1 mufflers, verifies my OK on this setup, and buys the mufflers and hands off the project to Sidewinder Racing. I was out of town, as usual.
3) Sidewinder Racing fabricates the exhaust, and adds the great bellows idea to the wastegate, as well as putting v-bands on the cat pipe. That's why they get the big bucks. It took them about a week to finish the project, but I'm not sure how much time was actually spent on the car.

Stainless is very difficult to work with because everything must be cut flush in order for the welds to last. This is why it was contracted to a leading race shop. This is also quite expensive. There is a reason why the good 20B conversions cost over $30,000.

Hehehe, I'm just using the N1's because they are good, quality mufflers. They do look pretty rice, if you ask me, which is even better to annoy the Mustangs and Camaros. Note that I have dual "N1" mufflers, not "Dual N1" mufflers, which are a different product. You may like the "Dual N1" mufflers better because they are a little smaller in diameter. BTW, the guys at Sidewinder Racing call my car "The Grapefruit Launcher".

Um, the foot was probably dirty.

 

Ha...I give up on the rotarygod thing (I hope you know who I was talking about ...either way he knows who he is).

As for the N1's...there I go again not being specific enough. I know the DualN1's are different from what you have, I was saying that I do like what you have going on there (it's not rice...that's a culture/characteristic not a product ), but it's a bit too large and shiny for me. How much have you spent on your 20B setup so far...dare I ask? *braces himself*

 

I know who he is Are you talking about my q-tec equipped Warlock muffler? I never got around to putting it on. Its just sitting on the floor. I need to get it done but the weather has really sucked lately and when it is good I am busy or gone. I can take a picture of it to show you what it will look like though.

 

Oh, I see, you meant the forum name "rotarygod". Well, I guess I was wrong, we DO have a regular member who is a rotary god, LOL.

Don't worry, it wasn't anything you typed. I just made the N1 clarification because I didn't know if you, or other members, realized the difference. I try to make most of my posts understandable to everyone reading the post whenever possible. Also, the fact that the picture of my exhaust is linked to the Dual N1 exhaust listing at the RX-7 Store adds to the confusion.

I'm not on my computer with Quicken right now, but I've spent about $30K on the project so far, and I still have maybe $2-3K remaining to get it on the street. Note that the $30K includes a lot of things like a full Mazdaspeed race suspension, full SPA digital gauge set, pro-built roll cage, and other items that most people would not put on their personal 20B project. A racing transmission, driveshaft, and rear end are going to add another $10K or so for phase II, and then about another $10K for phase III which includes the flare body kit (absolutely required for traction), paint, wide wheels, racing tires, and upgraded racing brakes. That's not really all that bad when you consider that a top-running SCCA EP RX-7 costs about $50K to build.

 

Nice, I was thinking of doing nothing but MAZDASPEED products on my FC but haven't really made a decision on whether it'll be this one or the next one (which most likely won't be far off once everything gets back in line). Thank God for sites like Corksport for just having obscure things that people don't think about much like suspension and all of the other important things that people take for grantid (spelling? or is the word really that ugly??? wtf). Most people just over the cosmetics, but I want the real meat of it all and I've already been to there site and seen all that they have for the FC ($$$...but it's soooo worth it). Putting an A-spec sticker on the side of the car and having it belong...priceless .

True though you haven't really spent too much on the car (is there any such thing ) at all. Keep up the good work man...

 

Oh yea, glad you finally figured out who rotarygod is haha...and btw do you have any pics of the inside of the car?

 

Click on the "Cage, Seat, Fuel Cell" link. Those are old pics, but the interior still looks pretty much the same now. I haven't installed the gauges yet because I want to make the composite dash panel and e-fan shroud at the same time, and I'm not finished with the fan shroud buck. I'm also going to install a Momo steering wheel, but that will be one of the last things I do because it's just going to get trashed if I install it now.

Attached is a proposed gauge diagram. I don't have the trans temp or brake bias gauges yet because I won't need them right away, but I have everything else. I'm still going to need to sit in the car and move the dual gauges around until I get a setup that I like, but this is the basic idea. The current plan is mount the fuel level gauge on the A-pillar, along with a turbo tach (called an N1 or Ng gauge in aviation lingo) if I can find one that is affordable. Here is the link to the SPA website if you are interested:
http://www.spatechnique.com/

 

Forget cosmetics; polishing just reduces surface area, which reduces cooling capacity. Besides, race cars are supposed to look good from far, but far from good.

Hehehe, I don't know about A-Spec. My car would belong in the SCCA SPO (Super Production - Over) class.