Jush

iTrader: (2)

Hey all, My 7 will shortly (hopefully) be on the road, and that being said, I would like to weld up my own exhaust system, all straight pipe. Where I live I do not need an etest, so, that's not a limiting factor.

I mainly would like to know what the ideal free flowing but not torque sacrificing diameter would be. I will be getting a header first of course. but after that I'm lost. I know that turbo cars are pretty much slap a 3" on and run like hell. But I've been reading and reading and to no avail have I found ANY info on exhaust piping diameter.

It's stockport, so I was thinking that maybe a 2.25" system to side exit pipe. that's with the 2" collector at the bottom of the header. But at the same time I think maybe something smaller than 2" would be better to keep low end torque? I have no idea. I'm not concerned about noise, I know it will be loud, I just want it to perform better than the full stock setup.

I've also heard that keeping each rotors exhaust pipe (?) separate for longer also does good things.

I know you're gonna say get the RB exhaust system and I'll just chuckle at the thought of spending that much on an exhaust system, let alone the shipping to Canada. NOT saying anything bad about RB I just don't have that much cash to spend, maybe one day, but for now this will have to do.

Thanks
-Josh

Jeff20B

iTrader: (13)

Dude, this is an awesome idea. Straight pipes on rotors are a blast! I can't wait for a video.

Jush

iTrader: (2)

That's awesome haha Thanks I will certainly get a video up, I just need adequate backpressure, that's the key in this situation. I think..

Cookboy

iTrader: (10)

If you search 'rotarygod information exhaust tuning' in the NA Performance section you'll find a very informative thread on exhaust tuning. It's all you need to know on the topic.

Jush

iTrader: (2)

THANK YOU.

I never would have found that otherwise.

This will get very interesting!

Will post a video here when it's all said and done!

KansasCityREPU

iTrader: (9)

This was used on a RX-3 drag car. Doing something like this. I'll sell you this one.

j9fd3s

iTrader: (3)

the C&D Rx2 had something like that on it, and let me tell you, its the loudest noise i've ever heard.

it was kind of funny to hear this noise that was louder than the whole pack of Mazda's rotary race cars put together, and then this little Rx2 comes around the corner....

the recipe for maximizing torque is pretty simple, you need to run 2x2" pipe, the RB stuff is thickwalled, so it ends up about 44mm ID, which is perfect. run it to the diff, and collect it, (90-125" depending on weather you go under or over), and then since its just a stock 12A you could collect into a 2.25 pipe and muffler of your choice.

since this is basically the RB street port system, its easy to suggest it...

Jush

iTrader: (2)

Like I said, I want side exit, I want to avoid the axle at all costs. I think if I kept it thin and made a box somewhere after the collector I could achieve the same results as a full front to rear system.

Again, stock port.

all be it, That ^ Is awesome haha.

MosesX605

This will be so f#cking loud that your head will explode, your neighbors will hate you and you'll generally be regarded as a giant dick for driving such a monstrosity.

Don't be an *******. If you're driving on the street, keep it quiet.

Jush

iTrader: (2)

I generally don't drive like a dink regardless, but there are times when you gotta have some fun, otherwise what's the point. I'll probably be too scared to let it rip all the time anyways, I can imagine the unnecessary heat it would draw on myself and car.

Not my thing.

Back to exhaust!

Collector diameter is 2.5" so, I think maybe reducing to 2" then into a box (read rotarygods thread and you'll know what I mean) to 2.5" outlet to atmosphere.

Or possibly just a full 2.5" system with a differently dimensioned box.

Haven't fully decided how I'm going to tackle this either, I may do a mix&match setup where I'll have 3 seperat sections ie. header, reducer/box, side pipe. With probably 2 or 3 different options each so I could have as much as nine different setups with only a few different sections.

MosesX605

Look,

I've been down this road before, more than once. Any combination of exhaust that doesn't include at least two (2) silencers and one (1) muffler will be too loud for general street use. A system with no silencers and no mufflers will be so loud and so obnoxious that the cops will just wait at your house every morning to give you your daily noise ticket and your neighbors will start an eviction petition.

But hey, do whatever you want.

j9fd3s

iTrader: (3)

no you can't imagine it. an uncorked rotary can be so loud, even at idle, that you can't even hear it anymore.

fire it up with just the header, in fact you must do this once in your life.

Spannerhead

iTrader: (1)

After the engine swap, I started my old '85 S with just the manifold on---at idle it deafened anyone nearby without ear protection and bought everyone on the cul-de-sac out of their house to see what was going on.

Ever been to a track day with a Spec 7 run group? Wow.

The funny thing is, when it comes to a naturally-aspirated 12A, the difference between optimized straight pipes and a quality, properly-silenced system really is a handful of hp at the most. So there's really no argument to be made for straight pipes from a power standpoint.

wankel=awesome

Its loud. Warned.

MosesX605

Once, I started my old race jalopy with nothing bolted to the exhaust ports. it wasn't that it was ear-splittingly loud, (it was) but the character of the noise was so atrocious that I never, ever, did that again.

Jeff20B

iTrader: (13)

I think this guy needs to build his exhaust as planned. Then provide a video and his thoughts/commentary. It will be a wonderous learning experience.

Jush

iTrader: (2)

I will never ever run the manifold only, I have done it, scared me half to death. The noise was absolutely atrocious as described. Like I said, around here, the police don't really bother with how loud your car is, unless you're being a dumbass, and even at that half the fart can ricers around town barely raise an eyebrow.

Again, I will most definitely make this a reality, I think rotarygod would be happy because no one was willing to try this out, if you read his thread, it was just a lot of speculation.

And if you think that there is only one way to do things ie. 2 presilencers and a muffler then you are sorely mistaken and somewhat close minded.

If you think about what mufflers actually do, (obviously muffle sound) but at the same time they provide backpressure and resonance, which is exactly what a hollow box would do as well if built to correct size and with many other variables in mind.

Let's use the RB exhaust as an example, Let's say you fiddled around with the numbers and figured out the flow pattern of the RB setup, you could just as easily copy the results with a shorter system with correct reducers/straight pipes. There is no absolute so saying the only way I can get good results is with presilencers and a muffler is a bit ignorant.

Please read the rotarygod writeup if you haven't.

Don't mean to step on toes I'm just saying that I'm not buying an exhaust system, when you say built not bought that means you built it with raw materials, not went online bought the stuff then "built" it yourself by bolting it all together.

And last but not least I'm not asking for legal advice, let me deal with the noise complaints and whatnot and I'll supply you all with the results.

Please?

(thanks jeff20b for the moral backbone)

Jeff20B

iTrader: (13)

You're welcome.

I think I'm being supportive here for two reasons.

#1 I actually build my own stuff. I just completed a custom long primary under a rotary powered MG Midget today. It's the most technically demanding/toughest exhaust I've built thus far, so if anyone out there can appreciate whatever you're going through contemplating fabbing a whole exhaust from port to tailpipe tip, and getting it to actually fit in the tiny space provided while not compromising flow potential, it's me right now. The 1st gen chassis is like way easier.

And #2, sometimes the best way we learn anything is to do it ourselves. I'm certainly like that. All I have to go on is what I think it will sound like as the car is not set up to run just yet. But I've built enough custom rotary exhausts over the years, both long primary and short collected, that I can make an educated guess as to what this one will sound like, and I think it will have a really nice exhaust note character like most long primaries do, while being quiet enough for the street without compromising flow (it has a streetport).

I've not tried rotarygod's exhaust box idea. I don't understand it very well compared with long primary length, pipe diameter, sound frequency/speed of sound whatever. You should go for it!

j9fd3s

iTrader: (3)

the box will work. basically sound is a wave, with a piston engine its like a nice sine wave, a rotary is going to be like a square tooth, but anyways theres a high and a low, and this difference is the sound.

what the exhaust box does, is basically provide a space where the waves can cancel/decay/whatever they do, and then the exhaust comes can come out of the other side in a steady flow, which is already quiet, and easy to muffle.

the box also decouples the header, so the "tuned" part of the system ends at the box, instead of the exhaust tip like it does without a box.

how big the box needs to be is an open question.... the FC uses this principal in the exhaust manifold design, so an under car box would need to be at least 2x?

oh lmao! buy two FC exhaust manifolds, you should get change back from a $20. bolt the engine flanges to each other, and then place in exhaust system, see how it works

Codysv6rx7

I'm sorry but I have multiple friends with straight pipes cars and I'm talking 3 inch all the way back on 240s rx8s and ya there loud when you drive fast but when you shift normally it's normal sounding I don't think name calling is required to point out you like your cars quiet some people like to have it loud

diabolical1

iTrader: (3)

i'll limit my participation to useless banter, anecdotal commentary and a break from stress. this seems to be one of those threads where the author composed it already having the answers that he/she wants so no on-topic discussion is required.

it's your car, your time, your life and your experience. knock yourself out!

agreed. i have done it on a handful of occasions. i'm tempted to say that the sound stops time. it assaults ALL of your senses simultaneously. the idea of the flashbang probably came from someone that raced rotaries.

and ... agreed.

j9fd3s

iTrader: (3)

what did the rotary race driver say to the other rotary race driver?

diabolical1

iTrader: (3)

huh?

j9fd3s

iTrader: (3)

what?

sleeping-7

iTrader: (31)

Give this thread a read, you'll find it pretty usefully in setting up you exhaust... https://www.rx7club.com/1st-generati...risons-823229/