i have had my new exhaust system for about 3 months now.

it is consisted of a racing beat header, racing beat presilencer, 2.5" piping without cats and is finished off by a dynomax performance muffler.


i got great power gains from it and i am still happy with it, however i am considering getting a 2.5" y-pipe and making it a dual again.

the performance wouldnt decrease all that much and i think the car would be a bit quieter. I would like it to be a bit quieter because i have already gotten pulled over once in the city for a noise violation and it makes me scared to stomp on it.

plus not to mention the dual looks a bit sweeter on the FC.

so should i leave it as it is or go ahead and make her a dual again?

 

Make it dual. I think it looks 100x better. I'm sure if you lose anything at all you won't notice it.

 

A quick check on the math will tell you 2 2" tubes have almost exactly the same flow as 1 3". I personally prefer the dual look, and am running duals all the way back. You were right to go with the RB presilencer.

 

Dual looks better.

 

Actually going from a single 2½" pipe to dual 2½" pipes will probably increase power because of reduced backpressure (assuming properly tuned extractors), and reduce noise because each muffler is only dealing with half the noise energy.

 

You have to consider the turbulance created when splitting into two pipes. One single pipe the whole way will result in a straighter flow, therefore more top end power. However, the power loss would be minimal, if even existent and the sound reduction would be a good improvement.

 

The restriction from the turbulence created is going to be more than offset by the fact that flow area is being doubled.

 

Which Dynomax muffler were you running? And to what are you comparing the noise to? I'm in the process of building a single the exact same way you did with the racing beat combo and a single with the Dynomax muffler. I'm running one 2.5 in/out stainless steel ultra flow (I got from summit for $75). But now you got me scared that it is going to be too loud. I'm hoping you were running the race muffler. But what set-up are you comparing it to anyways? If you are comparing to a Racing Beat dual set-up then it's easy to believe that it would be louder. But what about compared to an Apexi N-1; is it louder than the N-1? How about the N-1 Dual? How about any others you've heard? I'm just trying to get a feel for the noise level; and I haven't had anything welded yet so I can still change my mind. Throw me a bone man. Thanks.

 

Not sure about the power increase- OK, There is MUCH more cross-sectional flow area....3.97"^2*2 (7.94"^2!) , for the dual 2 1/4", compared to 4.9"^2 for the single 2 1/2.

You will probably get more power from the single 2 1/2.

It's a common misconception that bigger exhaust=more power... especially on a rotary. That's true to a certain extent- BUT you need to maintain exhaust velocity. That's the name of the game. Too big and you get no scavenging effect.


Also- the exhaust should ideally be SMALLER near the end of the exhaust stream, since the exhaust cools and is denser (smaller) . Mazda DEFINATELY doesn't have the best system with their stock exhaust.

Your header outlet and pre-silecer will also still be 2 1/2 inch... so if you are expereincing any restriction (which I doubt) it would still be tied up there, no matter how big your y pipe is (the weakest link in the chain...)

There is also a boundry layer around the inside edge of the piping, where flow is much slower due to turbulance and cohesion/friction.
I don't know the formulas for caluctating that, but in reality, one single pipe, with the same amount of volume as 2 smaller pipes, will flow better.

Anyways... I just realized I don't really have much of a point here, and I'm rambling on...considering these are only slightly larger than stock sizes... but anyways, my 2c's.

And to mess everything logical up that I just said- I noticed a difference when I went from a 2" Y-pipe to a 2 1/4". So there. I could argue with myself all night!

 

Either way we're dealing with minimal changes in power. But major changes in noise! The noise is what concerns me. We already had this debate a few months back about the single and dual issue and in the end everyone just said "Do what you want" so I am suggesting we don't go that route this time but get some feedback from people who have had both. All those mathamatical equations mean poop when someone who has done it in real life states the exact opposite of what the equation says. I alrady had two dual set-ups and now I want to try out a single for awhile. Save a lil weight and simplify the system also. Less gaskets and less hangers means less trouble, less leaks, and less ratling.

And I kind of like listening to people argue with themselves; it's honesty in its' purest form.

 

mot this crap again how many times do i have to read this it's always the smae argument someone says yest duals look better and might flow more then someone always has to bust out the triginomicalcalulus and say oh actually or no that's not right man that burns my bung hair

james

 

I have a 91na with working VDI & working 6-ports with a 2-outlet header and 2" dual all the way back. Two heavy presilencers two cheap bomb mufflers. Low end pull (where I mostly drive) is strong, and when I air it out, it pulls hard all the way to the ~8200 buzzer. Sounds good. looks good, runs good. If you pick up a miss, you can tell if it's #1 or #2.

 

You are not going to get significant noise reduction if you keep with the same mufflers.&nbsp Noise reduction is more a fuction of muffler design...



-Ted

 

On the side of the Dynomax muffler box I got; it had a chart of the Dynomax muffler versus three other brands (Borla, Flowmaster, and one I can't remember). According to their lil chart, a static test done at 3000 rpm's prooved the Dynomax SS Ultraflow to be the quietest muffler on the market for it's flow rate. It has around 2 inches of stainless steel mesh that wraps around the center tube then another 4 inches of fiberglass around that. From every resourse I could find; this muffler is "supposed" to be the quietest one you can get with a straight through design. I sure hope it is.

 

i think i am using the race mufflers. i have heard a 91 NA with A'PEXi duals and it sounded much better. less weedwacker sound and more of a deep tone.

 

Here is a little thing from APEXi to stir up some controversy about the whole single vs. dual war:

 

lol 787B, your avitar is my background!

 

So do you guys think that little comparison is just a cheap advertising scheme to get you to buy the more expensive system, or do you think its legit info? I know its a 3rd gen system but it shouldn't much different.

 

it is my wallpaper most of the time too!

 

Actually it's for a JZX90 Toyota Mark II, like this!