Guys i want to put togeather my own exhaust.I want to do straight pipes from either the cat back or the header back.What do you think i should do. Do i have to remove the mufflers?and what would i need to clear the check engine light if it comes on.Someone here did it and people who saw it said it sounded good.Also i dont want to lose any torque...so what set up should i go with.

 

Removing the CAT and driving the car on the street is illegal and can cause warranty problems. Outside of having a VERY loud exhaust what do you hope to achieve? Racing Beat dyno tested an RX-8 with no cat & muffler and gained a whopping 8 HP. BUT if you plan on keeping the CAT & it’s sensor what you could do is pick up a used OEM muffler from a member cut it open; remove the insides and route the tail pipes right to the inlet opening. I have not done this but read a thread here a while ago from someone that did. I think if you search under “ Home made Exhaust” you might find it. By the way I have a used OEM exhaust here in Jersey, if to what to take it off my hands for $40

 

Before you go doing a straight exhaust system, I suggest you go to an SCCA race somewhere and listen to ALL the RX's of different vintage WITH the mufflers they have to run. If the 8 is anything like the older rotaries, you won't be able to stand within about 3 miles of the car at 5000 RPM and a straight pipe!!
As much as I love my 8, at places like Daytona, with garages, we won't let ANY of the rotaries crank up inside the garage. Keep in mind they HAVE mufflers for racing and they do permanent hearing damage running inside the garages! They make my straight pipe formula ford sound about like a sewing machine.

 

If you want to build your own system, that's cool. Go for it. No exhaust is going to give you big power gains though and it is debatable if you can even feel it. The advantage you will have if you build it yourself is price. This also assumes that you can weld. It isn't too hard to get a muffler that works well but still flows good. Removing the cat is not street legal but if you wish to run without one, you will need a O2 simulator so you don't get a CEL. Some people have actually reported no CEL without one but the odds are that you'll get one. Do not expect any massive power gains from an exhaust. Without going into great detail and length about port overlap, port design, siamesed ports, and turbulence, you're just going to have to trust me.

If you remove the cat and replace it with a straight pipe, the MAX power you can get out of it is about 7 hp. If you remove the muffler and replace it with a straight pipe, the MAX power you can get is about 4-5 hp more. If you replace the factory exhaust manifold with a header, the MAX gain you will get is 4-5 hp. All of these numbers are PEAK power. Average usable power will change even less than this but generally you won't even see a hint of gain until 7K+ rpm. All of these numbers appear to add up to about 17 potential hp more than stock. However, it doesn't work like that. When you put all of this together, you really only get about 10-11 hp more at peak rpms.

The stock exhaust size is about 2.5". Don't go up to 3". It won't help power at all since the engine can't flow that much anyways. It will make it harder to muffle though. Be careful about which mufflers you choose. It is possible to use a new exhaust system but lose power over stock.

So far all creative attempts at exhaust design have yielded the same result and that is about a 5 peak power gain. That's hardly worth the effort and certainly not worth the money. I like seeing original work and would love to see you build your own system. Do it because you want a certain sound though. Don't expect to gain any feelable power from it.

 

i have a thought on that sound thing... check your pm's RG

 

would i be able to do straight pipes while keeping the cat and stock mufflers?...how would it sound

 

im doing it for sound....i want it to sound like a beast....the thing is..i dont want it to be too raspy and annoying..i want it loud..but deep ...not really raspy...my cousin put straight pipes on his 03 M3 and it was loud but very raspy...it sounded like he had rocks in his exhaust and they were banging against the metal..

 

Straight pipes AND keep the CAT & stock muffler??? Your losing me here. If you just want a nice sound why not just replace the stock muffler with a Borla or Greddy.

 

Sorry i dont know how the whole straight pipes works....i want like that Formula car sound....none of the exhausts i hear offer that.

 

I have the Greddy, sounds great. I get popping depending on how I am driving, loud over 5,000 RPM but civilized when I need it to be. The attached photo is of my stock exhaust, look at that pipe that goes from the CAT to the muffler, not too many bends. My advice is get a Greddy or Borla.

EDIT: FYI what the Greddy exhaust looks like

 

I have a video of my cousins M3 with straight pipes and no cat....if anyone wants to put it up

 

You can see for yourself how the car sounds without its muffler, just break the flange open behind the header, and move the cat converter and resonator pipe to one side.

Wire it aside and take it round the block. Besides being VERY loud, the raw un-muffled, un-resonated rotary sounds extremely nasty, and very raspy. You won't like it, and it sounds nothing like an M3!

Like RotaryGod suggested, there is nothing to be gained from going larger than the stock 2.5"ID piping, you should concentrate on the muffler section.

S

 

Why invest in a new exhaust when there is no real gain except the sound? Think the stock sounds just fine, well my 71 year old mom says my car sounds funny Can't see 850 or so for a bit of sound??

 

Paid $540 for my Greddy

 

straight pipes would be cheaper to put togeather than any exhaust i could buy....dam i wish i could just hear it to make up my mind

 

Are you even reading our replies to your original post? For the third time you can disconnect your muffler from the exhaust system temporary and tie it to the side for testing purposes. The noise will not be much different with a short exhaust system. If you bothered to look at the pic I posted of a stock system unless you plan on running the “straight” pipe under the rear suspension you will have to have a bend to get around the rear axle.

 

I was hoping i could just hear a clip or something instead of having to take my car to a shop to get the muffler removed temporarily....i read all the posts and i looked at all the pics...relax...cut down on the sugar....like i said im not too familiar with this set up ..thats why im asking questions....geeze

 

Why would you need to go to a shop for this test? Two bolts are all that connects the outlet flange of the CAT to the rest of the exhaust. It would take a mechanical novice five minutes to unbolt the exhaust system. FYI I am doing Atkins so I use very little Sugar :-) But I do have a two-year-old that likes to toss my keyboard & mouse on the floor
It just seemed to me we were giving you the answers over and over.

 

No problem boss i understand......i just wanted some opinions