0001tmn

iTrader: (2)

how big is the piping on a stock 82? cause i'm trying to put a new muffler on to fix some of my rattling issues,

Super82

iTrader: (1)

It kinda depends where in the system you're talking about, but lets just say its not as easy as putting on a new muffler. The pipes that go into your muffler are 1.75", I think, and there is two of them at like a 45* angle. The pipe before it splits is 2". You won't be able to just slap a new muffler in there without some fabrication.

mazdaverx713b

iTrader: (91)

i would just buy an o.e fit muffler or upgrade to the racing beat muffler..dont dick around with universal mufflers

Super82

iTrader: (1)

Yeah, I have to agree here. Now I think on the 79-80 and the 83-85s all had single inlet mufflers that would be easy to swap out for a universal with a tad of creativity, but on the 81s and 82s its a bit more difficult. I've been planning on switching to a magnaflow but without having a pipe bender and a welder on hand you have to go to an exhaust shop and they'll rape ya. Besides, its always going to be a bit riskier with a universal muffler. Your best bet is to go with RB.

mazdaverx713b

iTrader: (91)

a cheap universal muffler will not be able to stand up to the heat. it will burn all of the packing out VERY quickly and can actually make the engie sound like ****. go with the racing beat muffler.

the rattling issues are more than likely caused by a bad converter heatshield or hardened exhaust hangers.

0001tmn

iTrader: (2)

well i got 2 magnaflow mufflers and friday i'm just gunna go to the exhaust shop and have a new 2'5 inch from manifold back made with my mufflers,

Super82

iTrader: (1)

Hmm, you sure that they are going to do that? They'd need to get rid of the cats and in MN that is grounds for removing their license. No shops will even touch my car without the cats. I know other people may say different on here but 2.5" is getting up there, too. Make note that its kinda big and could kill your flow speed. I run 2" and I haven't heard any problems with it.

0001tmn

iTrader: (2)

here in NC thay dont care you just tell them its a race car and thay wont think twice about it, and i want 2'5inch cause its cheapest, 2,25 was almost 30$ more for some reason,

SCCAIT7

Kill your flow speed!! WHAT!? I am running a 3'' mandural bent with a racing beat header ... The racing beat header is designed to pull the exhaust out of the engine.

Example: Take a staw from the gas station. Standard clear one. Blow through it. very hard to blow through right?

Now - Go to one of those fancy places where they have bigger staws -- blow through it ... Easier? Yes - Very -

You do NOT want to restrict the exhaust - having small tubes only slows it down.

Do not concern yourself with back pressure. Its all BS.

What you need to do is order a header and then go to the muffler shop. The stock cast iron boat anchor doesn't flow worth a damn... There are a couple headers on eBay right now - I would do that - then go do your 2.5 if you want -

PercentSevenC

Here's some good articles for you and others to read if they haven't yet. Pay particular attention to the section about velocity in the first link.
http://www.yawpower.com/jantech.html
http://www.yawpower.com/febtech.html

I'm not actually going to say "this size is better than that size," because that depends on a lot of things, but exhaust tuning is a lot more complex than you seem to think. My recommendation would be to stay under 2.5" for a street-driven NA 2-rotor unless you have a radical port job.

rotary84

iTrader: (4)

interesting.... learning more and more

SCCAIT7

Spent many hours changing exhausts on the dyno and playing with EGT's.

Super82

iTrader: (1)

Its obvious you have no idea what velocity actually is. If what you were saying is true, then we'd all be running straight headers. With just headers there would be no 'BS backpressure' and the exhaust would flow freely out the back. But the truth is that doing so would hurt your performance, alot. A proper exhaust setup doesn't just freely move the exhaust out the back but actually speeds it up and creates a flow of which more exhaust can move out than normally possible. Having small tubes does NOT slow your exhaust down at all, it speeds it up. Try putting on a .5" exhaust, the flow would be so fast thru there you couldn't even have your hand behind the pipe, where as if you put a 10" exhaust on you would even feel it, it would feel like a slow flow of hot air. This is why running a 3" exhaust is not only overkill but is actually hurting your performance unless you are running a big dog 13B with all the goodies. On a 12a, there is no need for more than 2.5". Infact, I'd say if your on the stock ports stick to 2", thats what I'm doing and its working great. Maybe you need to spend some more time playing with straws.

0001tmn

iTrader: (2)

well i'ma put a 2.5inch exhaust cause this isnt a race car and i really dont care if i lose 2 hp.

PercentSevenC

I think 2.5" Racing Beat pipe is a good compromise. It has an inside diameter of 2.25". Plus, you get the benefits of thickwall pipe, which are significant on a rotary, believe me. But Super82 is right, if your ports are stock or mildly ported, then 2" works great.

Super82

iTrader: (1)

2.5" will probably be fine, especially if its RB piping like Percent said, but since it isn't a race car I think the only power you could be losing out on is low end streetable torque. Something to think about.

trochoid

iTrader: (6)

Before we all get into a pissing contest, both of you are correct in some areas and incorrect in others. While velocity is key to extracting exhaust, and hp, heat is also a factor. The main principle behind headers to work is tuning the tube length. As one exhaust pulse passes through the collection area, it creates a negative pressure wave to help pull the next pulse behind it. This is why equal length tubing with minimal bends is so critical, as is maintaining similar heat ranges between pulses.

If the tubing is too small, there's too much restriction, if the tubing is too large, too much heat is lost along with pressure wave tuning. Tubing size is also dependent on porting/overlap and desired peak rpm range. The later is probably the most important aspect of header design. As a general rule, the longer the individual tubing before collecting, the better. The more overlap, shorter and larger diameter tubing is needed before collecting.

Stock exhaust pipe is 1-7/8" ID. For a good read on exhaust tuning, SgtFox has the book "How To Modify Your Mazda RX7" on his website.

0001tmn

iTrader: (2)

i got my muffler installed. sounds no diff cause my exhaust leaks. all the gaskets are gone in it so once its fixed it would sound pretty niffty i have a video but its not that great cause its dark,but i'll upload it latter.

0001tmn

iTrader: (2)

http://www.youtube.com/watch?v=P3U_pKZNq38

http://www.youtube.com/watch?v=ALquZ0zB4VQ

1st one was around 6k and 2nd one was after it ran for a good 20mins. i reved it to high kinda cold

SCCAIT7

Best wishes. I am glad you got it done.

0001tmn

iTrader: (2)

i like it myself i dunno if its just the fact that theres leaks after the manifold or what but it sounds dang nice. not loud what so ever

Jeezus

iTrader: (4)

20 posts no real answer?

Nice muffler sound though!

PercentSevenC

What do you mean? Super82 answered the original question nicely.

j9fd3s

iTrader: (3)

the single part is like 1.75" OD pipe

the 81-82's have a dual pipe, midpipe, and i'm not sure what that is

0001tmn

iTrader: (2)

wait...81-82s have duel pipe? mines a 82 and has a single.