DrKillJoY

Here is the layout of the RX-8 exhaust system, any ideas about how to route a hi-flow system from you guys with experience?

hajami

How about removing the secondary cat? That should give slightly better exhaust flow.

DrKillJoY

what about retaining the cats, or replacing with a high-flowcat..

trying to stay legal...

--- what about that big honking muffler back there..

hajami

The muffler design look similar to the one on the corvette and I have seen many aftermarket ones to replace it.

Depending on how much space there is down there with the driveshaft and rear axle, might be able to split off to dual pipes earlier, eliminating any sudden 90 degree turns.

wakeech

i'm not going to guess at how much improvement over stock you can get and still stay legal, but certainly you could save some pounds by gettin' rid of that huge dual tipped muffler and switched it for (some kind of) regular one-in-one-out...

said7

How about placing a hiflow muffler in the spot with the secondary cat is and having just pipes to the rear.

Seems efficient and probably would be pretty loud.

rotarynews.com

How about this... 2 small straight through mufflers (had theses on my old FC.. very loud!)

I'd like to see how much room there is under the car... (I didn't see one on a lift or anything at Laguna Seca) so the Y pipe could be made straighter, and start further up towards the engine.

and get rid of the cat ... for racing purposes only .

DrKillJoY

nice PS job Dan..

I like that..

I still hate that alst 90 degree bend tho'

rotarynews.com

Actually, I use the Gimp... Remember, I'm a Linux only operation.

And, yes, I hate the 90 bend too.. maybe something like this...

TerenceT

it depends on where the O2 sensors are placed too

it'll be very likely to be put on the second cat. we can use a high flow cat and some kind of electronic fix (reisistor fix)

depends how much space you get at the cavity, you might fit a small muffler in the center section, making it 1 in 2 out?

btw, doesn't it mess up the weight ratio? cuz removing that big o' can means your back end is now 40lbs lighter

also, what's the exhaust diameter? seems like 2.5"

that means aftermaket is going to sell us 3" mendrel bend big muffler with 2 tips at round $1200

i think i'll opt of a hi flow cat / 2.75" crash bend piping and some kind of dual exhaust can?

fritts

From the literature in the press kit there are actually 2 O2 sensors one before and one after the cat I believe. There is also just one cat. The piece you see at the header position is actually a resonator. I would say make a set of headers to a straight pipe back to a single tip high flow muffler. We can't be as bad as a damn SUV for the environment plus in Indiana we have no tests, so na na aboo boo.
Save weight and get a high flow system. Also the weight you loose in back I don't think will hurt to much especially if you replace the resonator with a real set of headers, so you lose weight on both sides of the car..

b2k2000

Maybe we can get someone to make a trick rear valance for a single center pipe configuration, can someone alter a photo of the MazdaSpeed rear photo (I am at work with no photo editor here) with one single pipe out the center, kinda curious how that would look

TerenceT

btw, what does the rotory headers look like?

b2k2000

normal headers, only there are only 2 pipes, similare to a 2 cylinder engine

Slickvic

BTW Fritts, all new cars have to have 2 O2 sensors to be ODB2 compliant.

Fëakhelek

Thanks for clearing that up. I have a resonator on my Probe that looks exactly like that. I thought about asking about it but I wasn't sure and I didn't want to look stupid like I didn't know what a cat looked like.

Quick_lude

We have emission testing every three years. I would not want to run a "straight" cat in this or any other vehicle just to gain 10hp.. It's really bad for the environment.. It's already hard to breathe in Toronto during the smog alert days, no need to contribute to that just to gain a bit of hp which really is meaningless..

DYT

Finally a voice of reason, not that it would change those people's mind

Quick_lude

Well I'm all for a more free flowing exhaust to get more power, I have one on my car right now. But at least with my engine, running a "straight" cat does not make any worthwile gains.. maybe 1-2hp. With the Renesis you might gain more since it's a rotary engine.. but really, is the extra 5-10hp worth all that pollution? For what? A little more power? I'd sacrifice that in a flash for a breathe easy summer.. No cats is a very irresponsible proposition imo.

That said the 90 deg turn can definitely be improved on.

DrKillJoY

I agree with the leaving of the cats in... the exhaust options I am looking at are in line with keeping the car in the vague realm of manufacturers warranty if possible.. so pretty much anything rearwards of the cat. convertor is fine.


* However I have to tell you that adding a "test pipe" (removing the cat) and freeflowing exhaust to my 1991 non-turbo car gained a heck of a lot more power than 10 hp.

fritts

I guess if I lived in a polluted city I would have an issue with it. But when SUV's and trucks are running down the road with large displacement engines, the overall volume of crap they put out has to be much higher than anything the renesis even without a cat would put out. I will remove my cats..

wakeech

i have a feeling that you could (if you wanted to) easily burn more gasoline than any SUV with a few races per week... remember that you're not getting 20mpg at 8k WOT...
without that cat there, your HC emissions are gonna go through the roof, and i've heard all sorts of horror stories from guys with 13B's and no cats (like how bad the exhaust stinks, and how bad it'll make you choke when you walk 'round behind your car)... you might be advised to get rid of the resonator, the muffler, and get a "high flow" (:p) exhaust system to go around the cat... these days, the catalytic converters aren't the same kick-in-the-nuts the air-pumped systems from the 80's were... you're not gonna see the same gains without a LOT of front end (ie: serious FI) improvement... leaving everything stock except for "high performance" (:p) filters and an exhaust, maybe a chip (which can't change nearly as many things in this engine as it could in high-tech piston engine), i'd say you're not gonna do much other than make yourself sick by guttin' or removing your cat.
rotary or not (whatever QL meant by that), it's not gonna see you big gains with mostly stock mechanicals.

fritts

The gains we see from high flow exhaust systems remain to be seen so I would not say that you will not see them. My choice to do what I wish anyway so just make sure your not behind me...

Also how much of your normal day driving do you find yourself racing during normal driving your emission can't be terrible.
Most likely still doing better than large displacements you see running around..

wakeech

*shrug* okay. you are right.

Quick_lude

Very incorrect. Just because the SUV's burn 20L/100km that doesn't automatically mean that they are terrible pollutants. Cars from 20/30 years ago pollute as much as 20 or 50 modern cars.. not quite sure about the number. If you take off the cats on the Renesis I'd wager any money that you will pollute a LOT more than any properly tuned SUV.

Btw, I believe that removing emission equipment on any vehicle is AGAINST the law.. maybe I'm wrong there.. Either way it's very irresponsible and ignorant.