Red*To*Rip

I have decided im going to make my exhaust at work.
What is the biggest i should go?
3" or 4"?
Should i use a bottle (resonator)??
Any preference on a muffler that sounds good.
Im looking for something that will be the most free flowing to give the most power gain possible.

Any tips on doing this or know of anyone who has used/using a 4" straight through exhaust?

Power gain differences between a 3" compared to 4"?
I dont really car how loud that car is

nu-rx7junkie

iTrader: (1)

what kind of turbo??? stock?? 3" large turbo ? high boost? 3.5 my 2 cents

The Shaolin

iTrader: (5)

2.5" n/a

3" turbo

scathcart

Biggest pipe you can fit on a turbo gives the least backpressure, and the best turbo response. I like a 4" downpipe into dual 3" feeding dual mufflers. Overkill on a stock turbo, but it won't hurt erformance, and it'll be there when you decide to upgrade.

I like borla mufflers.

wackaloo13

iTrader: (3)

i have a 4" straight through exhaust. its louder than my dual n1 w/ no cat/presilencer on the stock turbo, currently i am running a 500r on a half bridge. i run magnaflow mufflers. I run 2 in series. my center muffler is a bit low, i might toss it out and stick a piece of straight pipe in there to get more ground clearance. my setup costed me about 500ish and i have a crapload of stuff left over. that was 2 magnaflow mufflers, 5" tip, 2 45 bends 3' of straight and 3' of flex pipe. o and everyhting is stainless. my $.02 on building it is to hang the mufflers first and make sure you have the tip sticking out how you want it then do the piping.

what kind of power are you looking ot make? do you want to recirculate your wastegate?

Tofuman FC3S

iTrader: (1)

That goes for about the first meter of the system at most. After that if there isn't enough gasses (stock turbo) the larger diameter will cause the gasses to slow down, thus increasing backpressure again. The goal with designing an exhaust is to match it with the performance fo the car, to small diameter, and the gasses will travel quick, but under alot of pressure, to big diameter, and gasses will slow down, increasing pressure anyways.

Riz.

scathcart

While I appreciate your attempt at fluid theories, please make sure you're actually correct when you try to apply them. Straight pipe exhausts on a stock S4 turbocharger, both using a borla 3" muffler, showed a very small, yet present, lower backpressure under all operating conditions with the 4" downpipe. 4th gear pulls showed no measurable gain in aceleration. Turbo response was slightly better.

1 test beats all guesses.

Tofuman FC3S

iTrader: (1)

This was taken from Burns Exhaust Theory... I am however completely for testing, and the test you conducted shows the bigger diameter helps. Do you have anymore info on your test? Wouldn't the 3" Borla muffler act as a venturi increasing the speed of gasses anyway?

Riz.

SpeedOfLife

iTrader: (16)

To speed up the gases you HAVE to add energy to the molecules, plain and simple, despite the decrease in ambient pressure very locally, that added energy will be supplied by the pressure coming out of the motor. Bigger pipe should allow the easiest flow, even if the linear velocity drops a little bit on the way out. The rate of flow measured by VOLUME should be your concern, and a slightly lower linear rate coupled with significant increase in area of the flow pattern = higher volumetric flow rate. That, of course, may not hold true if you're comparing exhaust systems of different diameters yet with different lengths and or different bends and obstacles, like mufflers or cats.

Tofuman FC3S

iTrader: (1)

OK, that makes sense... Where would be the limit in diameter? If there is a limit (for a car-length system), wouldn't that change depending on the volume of gasses expelled? Or is with everything that is on the streets a 4" in the zone where it is efective? Why are all popular cat-back systems for FC 3"? I'm sorry for the questions, but it appears i dunno alot about exhausts, and I would like to be better informed.

Riz.

Red*To*Rip

hey guys, awesome feedback so far!!
sorry i didnt specify, my car is turboed and is making roughly 230whp.
i talked to guys at work and they said 3" is plenty big enough for the power im making and 4" is overkill.
should i run duals or just a single muffler?

MmSadda

iTrader: (2)

Use duals; better airflow, less unnecessary noise. I suggest using a Borla or RB catback at the end, assuming those are, or are made in 3" applications.

SpeedOfLife

iTrader: (16)

I personally think the duals look awesome, they just fit right with the FC. And yes they can probably flow better compared to a single 3" pipe as long as the two branches are plenty big on their own.

I agree that 3" should be sufficient. If you really wanted to go crazy maybe build a 3.5" system, but even that might simply be adding more weight than you'd gain in power to overcome it. The weight/power ratio argument though is also a reason to go with a single pipe.

afro88

iTrader: (2)

Hold on isnt the true dual exhaust completely seperate from eachother even from the header? So Would you run 1.5 individually or would you still run 3" for both? The mazda speed true dual looks like it's seperate...... sorry if this is a stupid question.

Personally I like the look of the single but if the dual is more efficient without sacrificing weight then thats what I will stick with.

SpeedOfLife

iTrader: (16)

You'd want to run at least 2" for the branches, because using 1.5" for each would most likely flow worse than a straight 3", especially if that means 2 mufflers instead of one.

Also, yes, true dual is not possible with a single turbo'd '7, but it could be done with twin turbo as long as each turbo is dependent only on a separate rotor's exhaust. NA you have two exits and can 'easily' keep it that way, but it'll be hellaciously loud, and a basic single exit open header NA is already quite deafening.

afro88

iTrader: (2)

The louder the better. I get free ear plugs from work .

lol maybe not that loud but I was kind of thinking that the single turbo used one down pipe (dont know why I didnt think of it earlier it' common sense) so single exhausts were available. Is the Re Amemiya one with the tip that points down available for the fc?

ericgrau

iTrader: (1)

10 feet of 2 inch pipe will cost you about 1 HP in an NA. 2.5 inch pipe will cut that down to ~1/4 HP, saving you about 1 HP or a little less. For a turbo, as a rough estimate, I'd increase those sizes by about half an inch to an inch. These are peak gains at WOT. At lower revs/throttle the gains are much less.

A simple exhaust will still provide tremendous gains, especially from the cat and mufflers. Beyond that I'll assume you've already spent thousands of dollars on everything else imaginable, and you're still trying to squeeze out every last horsepower. In that case go ahead and grab that last 1-2 horsepower using 3 inch piping, gigantic mufflers and smooth bends in the headers (any bend that isn't abrupt is fine even for extreme setups).

The forum search tool will give you more info and popular brands.

Red*To*Rip

awesome input guys!
i have an idea i think im going to stick with.
when i bought the stock n/a, it had a brand new 3 inch exhaust with 1 bottle from the header back into dual mufflers.
i think im just going to weld on the flange for the turbo and throw a nice set of mufflers on the back????
does it make sense to anyone else??

YaNi

iTrader: (2)

Area of tubing:
1.5" = 1.76 sq in
2" = 3.14 sq in
2.25" = 3.97 sq in
2.5" = 4.91 sq in
3" = 7.06 sq in

You can't just divide the diameter of the tubing in half when you have a Y-pipe.

Three inch to dual two inch should keep the velocity high.

Red*To*Rip

thats what i thought, its a pretty nice exhaust, big Y-pipe, so i think thats the route im going.
Any preferences on mufflers, something straight through though.
I used to have a megan racing muffler and really liked it, but nothing big than a 4" tip.
they are pretty strick on muffler size down here.

K!NCH

iTrader: (2)

Not to jack, but would a 3" be to big on an n/a. Like would there be a loss of horse power. The reason I was going to do it was because I plan on turboing my car later

ericgrau

iTrader: (1)

There's almost no such thing as too big for the pipe. It's just a waste, that's all. You should have no problem with 3 inch, but I think even on a turbo it's not that necessary. 2.5" is fine. Now if you plan on upgrading the **** out of your turbo and want to get your exhaust out of the way now, sure go for it. Btw, I have a friend that put an RB turboback on his NA. Just didn't use the downpipe, IIRC. Unfortunately he didn't gain anything b/c he didn't know about the 5th and 6th ports on his s4, heh.