rotarygod

I can come up with something simple for illustrative purposes but don't expect it to fit the car!

PhillipM

I've run 1 7/8" primaries, into 2.25" secondary, collected into 2.5" system just slighty further down.

rotarygod

That's how I'd do it initially. I don't see a reason to go to a 3" pipe when the total port area isn't even close to that.

PhillipM

2.5" is enough flow for anywhere up to about 270bhp or so anyway.

rotarygod

OK I took a few minutes to draw up my design in AutoCAD. I've converted it to PDF. Forgive the rotation. I'm just glad it linked! It gives an idea of what I'm wanting to do and I added a few notes to show my train of thought. The actual pipe length dimensions can and may very well end up outside of what I have listed when all is said and done. These are just my initial thoughts. Someone please feel free to build it, modify it, and either prove it does or doesn't work. I don't care either way. I just want to see it tried rather than someone to blatantly say "it doesn't work". You can't claim that until you have proven it doesn't. It might not but I'd be fine with that.

I have other ideas as well. One is a variation of this one but it would add another pipe that goes nowhere that gets capped off! I'll modify this drawing tomorrow to show what I mean.

The other 2 ideas are very simple. Just imagine separating the center port into 2 runners. Now you'd have a 4 runner header. Collect the front rotor pipes together into their own dedicated front rotor single pipe. Now collect the rear rotor pipes together in the same way. This leave 2 header pipes, 1 for each rotor. Now collect these 2 pipes right before the muffler. This would be a "long primary" system.

The last idea starts out the same way as the long primary but instead of collecting the 2 pipes before the muffler, don't collect them at all. Run them each through their own dedicated muffler. This is called a "true dual" system.

The last 2 ideas would be the simplest to test as they either work or don't work. The first 2 ideas could be modified with any number of pipe lengths and collector sizes and convergence angles. Just because 1 doesn't work right doesn't mean modifying it wouldn't work. It might. Those 2 would take some time to work out and in the end it may either be great or a whole lot of effort to learn what doesn't work!

Have at it world! If any of these work, remember where you heard about them. If none of them work, they were TeamRX8's idea!!! j/k You know I respect you!

Here's idea #1 that I first proposed after SS7.

PhillipM

Really should try and dyno ours on a stock manifold if we get chance, see how much difference there is.

drewski86

If you left the center ports separate, with basically zero pulse tuning, when a good pulse came through an outer port, couldn't you end up pulling exhaust back in from the center port? I don't see getting negative pressure in the chamber unless both ports are working together to pull the gases out.

rotarygod

I just caught a mistake in my notes on that drawing. Swap the pipe diameter sizes in the notes between colletors #1 and #2. I got them backwards. Collector #1 should be 2-1/2" and collector #2 should be 2-1/4". Oops.

rotarygod

Since the ports from each rotor open and close at the same time as each other, that's not an issue. The whole point of collecting them at a different length is to gain an acoustic benefit that you don't get at equal length. There is nearly twice the energy in the center port. There needs to be nearly twice the runner length to acoustically bring it back into balance. It's a bit more complex than that but that's the basic rundown of it.

drewski86

You know more about this than I do so you're probably right. It's just hard to imagine it working any other way. The gases through the center port may have enough velocity to fight being pulled back in, but it seems like it would be much easier for the pulse to pull from the center port rather than to cause negative pressure in the chamber. I'd like to see this actually put into use to see how it works.

It seems like the center exhaust sleeve can be widened a good amount which may make separating the two ports more effective. Are the sleeve walls solid to allow this?

rotarygod

The pulses through the runners are the same as through any other system. There is no delay between the center or the outer ports as all of the ports open at the same time in relation to rear rotor vs front rotor. All we are doing with these pipe lengths is to change the resonance point within each pipe. An equal length system with 3 pipes has 2 pipes in harmony but one that is out. That's stock. This way we have all 3 in harmony. It may not do anything though as 4 equal length pipes has been tried with little success and this is more or less a way to trick the engine into thinking it is a 4 runner setup.

You can never have a time when one port tries to pull other gasses back into it. In order for that to happen we'd have to have the engine on the suction side through one of the ports and that's not possible. When there is a wave travelling down the front port runner, there's the same wave travelling down the center runner too. When theres a wave travelling down the rear port runner, there's the same wave travelling down the center port too. The center runner sees twice the numbers of waves travelling down it as the other port runners do. Each wave travels down each runner the same distance over the same amount of time. Look at my diagram. From the engine to collector #1 is the same distance no matter what pipe you travel down. There is no opportunity for anything to get sucked backwards and the collector itself prevents this anyways due to it's shape.

The sleeve walls are very thin. In pictures it looks like the sleeve is thick but that's just a flange. In order to widen the runner you'd need to physically grind down the center plate itself. While it may sound like no big deal, you'd hit the water jacket as there isn't much room. It kind of sucks that there so little that can be done.

drewski86

That makes sense.

With the center port, would it be possible to block that coolant passage similar to what's done on the intake side with big bridges and pports. Obviously you would have to use something capable of withstanding the heat. That would give you more room to play with. Maybe I'm just dreaming. I just don't like to settle with mediocre.

rotarygod

I have already tried unsuccessfully to cut into and then repair the water jacket with no success.

drewski86

Thanks mazda

Benjamz

Im still working on my header, 1a and 2b will be together and 1b to 2a will be together. Still messing with the lengths but the dyno will let me know if it works or not. Kind of a W design. It will be 4 - 2 - 1. I prefer to look at actual test results to show me that things do not work.

Ben

P.S. I wanted to add that it will b 4-2-1 to go to the cat, but without the cat I will have a midpipe and exhaust to match the header to keep it dual to the back with seperate mufflers simular to the helix look. The header and the cat-back will have adapters if you want to keep the cat. Also it will have the flanges to mate up to the factory cat. But the adaptors are sleeve type and secured together with bolts on a bracket. So if someone wants to keep the cat they can and if they want to swap it out real quick it will be easy. The adapters stay bolted to the cat, and the two mid-pipes go between the dual header and dual cat back. Just trying to keep things simple and universal. I may have the prototype done by seven stock and if it is I will have it dyno tested and on display. "IF" it is done the car will be up on jacks and I will have a crawler so anyone can see how it looks on the car.

My site will be open I hope by this friday, if not next week for sure. I will be adding RX-8 custom products as I make them. Some of the custom RX-7 stuff on my site will give you an idea of what I have comming out for the RX-8.

An ETA on the header back exhaust system, I will start making it next week and I will have It at sevenstock for show with dyno results.

I will also have free T-shirts and pens, so look for me Ben with Rotary Extreme.

OpTiCaL

Good luck Ben! Any ETAs on any of that?

RG - ok the only thing left is lenght of the pipes. I haven't been under my hood or the car its self a whole lot lately and dont really know how much room we have to pay with... so are you thinkin header that automatically bypasses the cat or making it so you can still have a cat for those emission state guys?

alnielsen

iTrader: (4)

Somewhere I read that the optimum length before combining the tubes, on a 13b, was 118 inches. I bought a exhaust system, for my race car and the tubes came together just in front of rear axle. This was on a 1st gen 7. This was purchased, in the late 80's, from a company called Rotary Engineering in California. I don't think it is the same RE that is in existance today.
I think you are going to end up finding that a long tube header system will make the most gains. Nobody has tried this yet.

Benjamz

Well, I got delayed paper work wise in re-opening the business, but I'm working on getting the rx-7 stuff back into production. I hope to have some RX-8 stuff ready within 2 to 3 months. But I do not think anything will be ready for display at seven stock.

OpTiCaL

Sounds good ben... does anyoe know the velocity of the exhaust gasses? averge, peak, or what ever?

rotarygod

Cat? What's that? I don't even have a cat on my daily driven 2000 Civic! Screw the EPA! My mileage is far more imporant as it and not the air directly affects my wallet. I'm an environmentalists only when it's cheaper than not being one which isn't very often. You won't be able to fit a cat under the car with any of my designs. I'm aiming at power improvement if that's even possible, not emissions compliance. It's for "off road use only"!

rotarygod

This is one of the ideas I mentioned in post #205. It's called a "long primary" system and is by far my favorite 13B exhaust system.

OpTiCaL

Hahahaha, fair enough... with the smaller area of the middle port i am thinking the middle runner should be the smaller pipe and be 2.5 times longer... but i still need to try running some numbers... thinking the total volume should be teh equal... Thoughts?

neit_jnf

interesting...

PhillipM

Don't forget you've got two rotors worth of gas exiting there though, there's some serious velocity in the centre ports, and a fair bit of turbulance sending it into the walls of the header.

OpTiCaL

uh, yeah... smaller area = higher velocity... what are you getting at or suggesting?